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Introduction to PC's

Introduction to PC's

Manchester Computer Centre

November 1991 First Edition

Preface

Acknowledgement: The sections relating to MS-DOS have been extracted fro m documentation produced by the Oxford University Computer Centre and are included by permission and with gratitude.

Introduction

This guide is an introduction to Personal Computers or PCs. The term PC covers IBM PCs and compatible microcomputers or clones. The guide is in two parts. The first part covers hardware aspects of PCs, the second covers the use of the PC. Also included is a glossary explaining common terms and acronyms.

1.1. What is a PC?

A PC is a microcomputer. A PC is a single-user system, designed to fit on a desk-top; hence the word Personal. The IBM PC was introduced in the early eighties and since then has been modified and improved. Subsequent PCs have been designed to run any software written for previous versions of the PC. Many other manufacturers have produced compatible computers; that is, computers which work in the same manner as the IBM PC and use the same software. These are often known as clones.

The next section explains the various components that make up a PC.

Part A - PC Hardware

2. The Components of a PC

A PC consists of a main unit (or system box), monitor, keyboard and peripherals (see figure 1). Peripherals include devices such as printers and the mouse.

Figure 1 Components of a PC

2.1. The Main Unit

The main unit contains the Central Processing Unit (CPU) and various supporting Integrated Circuits (or chips) all of which are fixed to a printed circuit board (PCB) called the motherboard. The main unit also houses disk drives, expansion slots and the power supply.

2.1.1. The CPU

The CPU (Central Processing Unit) or processor is the `brain' of any computer system. In the PC it is contained on a single Integrated Circuit or `chip'. The CPU processes all instructions and data.

The CPU is driven by an internal clock. Simply speaking, every time the clock pulses the CPU processes one instruction. Thus, the faster the clock the quicker the CPU processes its instructions. Clock speed is measured in MegaHertz (MHz).

Most PCs will have a button on the front panel labelled `turbo'. This allows you to switch the clock speed of the processor. In the past certain programs tripped over themselves when the processor was running at high speed, hence the inclusion of a turbo switch to allow the processor to run at a lower speed. Nowadays, however, this is a rare problem.

2.1.2. Memory

All PCs are fitted with a certain amount of workspace memory called Random Access Memory (RAM). This memory is used for storing running software and data which the software requires, as well as the operating system. The contents of RAM are lost when the PC is switched off. For example, if you are running word processing software then the software and the document you are working on are stored in RAM. To save the document, after making any changes you wish to keep, it is necessary to copy the document from RAM onto disk.

RAM is located in chips situated on the motherboard. Most PCs come with 1 Megabyte of RAM as standard. However, not all of this is directly useable (see later).

2.1.3. Disk Drives

Disk drives provide a means of storing work, or data. Floppy disks are transportable from PC to PC and come in two sizes, 31/2" and 51/4" diameter. Hard disks are fixed inside the system unit and have much higher storage capacities than floppies. Disk drives are discussed in sections 4 and 5.

Information is stored on disk in the form of files. A file might be a program or data such as a word processor document. Files can be grouped together on disk in directories.

2.1.4. Ports and Expansion Slots

Located at the rear of the PC are various sockets or ports. These allow the keyboard and monitor to be connected. Most PCs include a parallel port (usually used for printers) and two serial ports (usually used for communications with other computer systems or connecting mice and plotters).

Also included inside the system box are expansion slots. These allow extra hardware to be added to the PC using printed circuit boards, or cards, plugged into the expansion slots. The slots are connected to the CPU via the bus. The bus is a set of wires which transfers data. Think of it as a motorway.

2.2. The Monitor

The monitor provides display output from the PC. Monitors vary in screen resolution and colours available. See section 6 for more information.

2.3. The Keyboard

The keyboard allows you to input commands and information into the PC. The keyboard is normally connected to the main unit via a 5 pin DIN type socket. See section 12 for more information.

2.4. Peripherals

As well as the essential keyboard and monitor, peripheral items such as printers and mice are often found connected to PCs. These are covered in later sections.

2.5. MS-DOS

An essential part of any computer is its operating system. An operating system is a program which provides the links between the computer hardware, the user, and software which is running on the computer system and controls all the components of the computer, including its peripherals. PC-DOS, Personal Computer Disk Operating System, is the operating system used on IBM PCs. Most PC compatibles, however, use the more widely available MS-DOS, MicroSoft-Disk Operating System. MS-DOS and PC-DOS are virtually the same. The use of MS-DOS is covered in Part B.

3. Classifying PCs

The first IBM PC was introduced in the early eighties and since then there have been many changes in the technology used by PCs and new models are introduced regularly.

PCs can be loosely grouped as follows, in order of time of introduction, PC XT, PC AT (or 286), 386, 386SX and 486.

The main change from version to version is in the type of processor (CPU) used. CPUs have increased in complexity and speed.(see table 1).

Table 1 Types of PC and Their Processors

Notes:

1. The 8088 is a slower version of the 8086.

2. The 80386SX was introduced after the 80386 and is a cut down version of the 80386 and is thus slower but cheaper. Since the introduction of the 80386SX the 80386 is now often referred to as the 80386DX.

3. Strictly speaking 386, 386SX and 486 machines are AT type PCs, since the change from XT to AT was more than a change in processor. The 80286 based PC-AT is now often referred to as a 286.

4. Once the manufacturing techniques used for a particular processor have been refined, faster versions of a processor can be produced, hence the range in speeds for a processor. Also, owing to a improvement in manufacturing techniques in general, processor speeds as a whole are increasing.

It should be noted that processor speed is not all - buying a PC with twice the clock speed will not double your rate of working; other factors such as disk access times are important.

Software designed to run on an XT should also run on any other type of PC but the reverse is not always the case.

3.1. Portable PCs

As well as differences in the processor used, PCs also vary in their physical shape and size. Most PCs are of the desktop type shown in figure 1. PCs are also available in portable versions. Portable PCs have the main unit, screen and keyboard all combined in one unit and some can be run from batteries as well as from mains supply. With the introduction of low power ICs and disk drives and the improvements in screen technology, portable PCs are becoming a popular choice.

A notebook PC is a smaller version of the portable PC and is usually A4 in size. Tower PCs are similar to desktop PCs except they are placed end on and rest on the floor.

4. Floppy Disks

Floppy disks provide a means of storing work. You can write information onto the disk and read information from the disk. Floppy disks are used by inserting them into a disk drive.

A light on the disk drive indicates when the disk is being accessed. Removing or inserting a disk while the drive light is illuminated may cause damage to the disk and is likely to result in the loss of data stored on the disk.

Figure 2 Tracks and sectors

Before a disk can be used it has to be formatted for use by MS-DOS. Formatting writes the tracks and sectors onto the disk's surfaces (see figure 2). A common combination is nine sectors and 40 tracks. Formatting a disk destroys any information currently contained on the disk. Floppy disks are normally double sided i.e. information is written on both sides of the disk. Formatting is covered in section 15.1.

4.1. Sizes and Capacities

Floppy disks come in two sizes, 31/2" and 51/4". Each size has two different capacities (see table 2).

Table 2 Floppy Disk Capacities

Double density disks are also known as low density, and high density disks as high capacity.

Disk drives exist for each of the four disk capacities. Usually XT PCs can only be fitted with double density drives (i.e. 360Kb, 51/4" drives and 720Kb, 31/2" drives), whereas all other PCs are fitted with high density disk drives.

31/2" floppies, as well as having higher capacities, are also more robust and compact and are to be recommended. More and more software is being released on 31/2" disks. PCs tend to come with a combination of one 51/4" drive and one 31/2" drive or a single 51/4" or 31/2" drive.

Disk drives are referenced by their drive letter. If your system has a single floppy disk drive, it will be referred to as drive A. A second floppy disk drive will be referred to as drive B. Hard disk drives are referenced from letter C onwards.

4.2. Use of Floppy Disks

Obviously 31/2" floppy disks cannot be used in 51/4" drives and vice versa but it also must be noted that while high density drives can read double density disks, double density drives cannot read high density disks.

For example a 51/4" disk formatted to 1.2Mb on an AT cannot be read by a 360Kb XT floppy disk drive. See section 15.1 on formatting disks.

Figure 3 Write Protection

Floppy disks can be write protected. This prevents any information from being written to or deleted from the disk and prevents the disk from being formatted. On 51/4" disks this is done by folding a sticky tab over the write protect slot; on 31/2" disks by sliding a plastic tab into the open position (see figure 3).

4.3. Handling Floppy Disks

If handled carefully, both 31/2" and 51/4" floppy disks are reasonably robust and can be used repeatedly without any problems. Disks may eventually reach the point when they should be discarded but this will normally be a few years. There are however a number of very important `dos and don'ts' relating to the handling of the less robust 51/4" floppy disks.

DO:

Protect disks from becoming dusty or scratched by replacing them in their envelopes as soon as they are removed from a disk drive;

Hold disks by the edges or corners only;

Use only felt-tip pens to write on disk labels that are already stuck onto disks (or, preferably, write the labels before sticking them onto disks);

Keep them in a plastic library case.

DON'T:

Bend floppy disks;

Insert or remove a disk while a disk drive light is on;

Use pencils, ballpoint pens or any other `sharp' writing implements to write on disk labels that are stuck onto disks;

Touch the exposed recording surfaces of disks;

Leave disks in full sunlight or any other places where they are liable to become too hot;

Stand anything (manuals, books, coffee mugs etc.) on disks;

Leave disks near magnetic fields such as telephones, dictation equipment, Hi-fi speakers, photocopiers, laser printers or anything containing an electric motor (including the PC).

4.4. Problems With Floppy Disks

A floppy disk which has previously been working without problems becomes unreadable. Floppy disks are liable to wear and tear. If you have trouble reading information from a disk, for example you may have a bad sector error, do not despair, there are utility programs such as those from Norton which can in some cases recover data from a disk with problems.

A floppy disks works perfectly well in one PC but fails to work in another. Check that both PCs have the same type of drives. i.e. you are not trying to read a high capacity disk in a low capacity drive.

Your floppy disk does not fit into the disk drive. You are trying to use a 51/4" disk in a 31/2" disk drive.

5. Hard Disks

Hard disks (or fixed disks) work on the same principle as floppy disks but are fixed inside the PC in a sealed unit. They can store a great deal more information than floppy disks and range in capacity from 10Mb to several hundred Mb. Access times (i.e. the time taken to read and write information) for hard disks are much faster than for floppy disks. Manufacturers often quote access times as well as capacities for hard disks.

A lot of application software requires that you have a PC with a hard disk and it is to be recommended.

5.1. Partitioning a Hard Disk

Hard disks can be split into different logical drives by partitioning. For example a 60Mb hard disk can be partitioned into two 30Mb logical disks, which can be treated as two separate drives, C and D.

Under MS-DOS (versions less than 4) the maximum size of the primary hard disk is 32Mb therefore drives of a size greater than this have to be partitioned (unless the hard disk comes with a special disk manager program). Partitioning can also be a way of splitting up the disk into more manageable sizes.

Most PC suppliers partition and format hard disks before distribution.

5.2. Problems With Hard Disks

Hard disks are contained in an air-sealed unit and are thus less liable to physical problems than floppies. However the consequences of any disk failure are much higher than for floppies so some form of backup must be carried out regularly.

All hard disks will have a number of bad sectors which will be marked as bad when formatting. The disk drive will not then write any information onto these sectors. Using the CHKDSK command (see section 15.3) regularly will inform you of whether the number of bad sectors is increasing. If this is the case then you may be having problems.

5.2.1. Viruses

Viruses affect can affect all your files whether on hard or floppy disks. A virus is a computer program that replicates itself by attaching to files. Some viruses can be relatively harmless, simply filling up the hard disk; others may destroy all the files on the hard disk.

Software is available which will scan through disks searching for infected files and repairing them if possible. It must be noted, however, that these programs can only cope with viruses of which they are aware.

5.3. Backing Up the Hard Disk

Owing to the much higher capacities of hard disks, backing up is much more time consuming. Backing up a whole 110Mb hard disk onto floppies is not really feasible.

A possible solution is to make selective backups i.e. only back up your work files or files which have changed since the last backup. MS-DOS comes with a backup program which facilitates backups.

A more expensive solution is to use a tape streamer which backs up the hard disk on to a tape. A 20Mb disk can be backed up onto a cartridge tape in less than 5 minutes.

Tape streamers can be installed into the PC, usually into a slot in the front of the PC. External, self-contained, tape streamers are available which can be shared by any number of PCs.

5.4. Disk Caching

Transferring data to and from the hard disk can be relatively time consuming, compared with the speed at which data is transferred in and out of memory and to and from the CPU.

Disk transfers can be reduced by using a disk cache. A cache is an area of memory where data commonly transferred to and from the hard disk is stored. If the data required from the disk is currently in cache then that data is called from the cache rather than from disk. Since transferring data to and from memory is a lot quicker than to and from disk, time is saved.

Disk caching is especially useful in disk intensive applications.

6. Video Displays

The original IBM PC was only able to display text and in monochrome only. There are now various display options available on PCs, some offering high resolution colour graphics. The display quality is dependent on the video card in the PC. The display is driven by a set of ICs called the video adapter or display adapter. This circuitry is contained on a PCB, a video card, which normally takes up one of the expansion slots, allowing the graphics display to be upgraded by replacing the card (and in some cases changing the monitor).

The resolution of a PC's graphics display is defined by the number of pixels, or dots, produced on the screen. The more pixels that make up an image the clearer the image will appear.

There have been several graphics standards introduced over the years which vary in resolution, colours available and cost.

6.1. Varieties of Display Adapters

6.1.1. Hercules Display Adapter

The Hercules standard has high resolution monochrome graphics with a resolution of 720 by 348 pixels. It is still a popular option due to its low cost.

6.1.2. Colour Graphics Adapter (CGA)

CGA was the first colour graphics option available on the PC. It has 16 colours available, but due to its poor resolution it is not a popular choice and is not widely available now.

6.1.3. Enhanced Graphics Adapter (EGA)

The EGA has high resolution (640 by 350) 16 colour graphics and is a vast improvement on CGA.

6.1.4. Video Graphics Array (VGA)

VGA offers higher resolution (640 by 480) and more colours (256) than EGA. Owing to reduction in cost it has made the EGA virtually redundant and is currently the standard display option on most new PCs.

6.1.5. Other Display Adapters

There are other, non-standard, display adapters available that provide higher resolution and more colours than the VGA standard. These include the 8514A adapter, which has a resolution of 1024 by 768 and up to 256 colours, and Super-VGA. Super-VGA, although not standard, has been adopted by many manufacturers as an improvement on the standard VGA display. IBM has recently announced XGA, intended as the successor to VGA. It must be noted that, as with other graphics adapters, the software you are running must be capable of driving the display adapters to get the full benefit of higher resolution and more colours.

As mentioned earlier, the video output from the PC is usually incorporated on an expansion card slotted into the PC. This makes it possible to upgrade the graphics on a PC with ease. It must be noted, however, that the monitor must be capable of accepting the signals from the graphics card.

A lot of software is designed to run on a particular graphics standard. It is necessary, therefore, to check that the PC has the necessary graphics card in order to run the particular package.

Most graphics adapters are downward compatible; for example a VGA card can emulate CGA graphics.

6.2. Monitors

Monitors are available in colour and monochrome versions and in different screen sizes.

It is necessary to have the correct monitor connected to the PC. For example a PC fitted with a VGA card will not work with a monitor designed for CGA graphics.

Multisynch monitors are capable of working with several different graphics adapters and at several different resolutions.

7. System Memory

Most PCs come with 1Mb of system memory (RAM) as standard. However the operating system, MS-DOS, is limited to using only 640Kb of memory.

Figure 4 Memory map of PC

The map of a PC's memory is shown in figure 4. As stated earlier, the operating system, MS-DOS, limits the amount of memory for user programs and applications to 640Kb. This is due to the limitations of the original PC's processor. When the PC was first introduced 640Kb of memory was perfectly adequate, but since then faster and improved processors have been developed, capable of addressing more memory, and the 640Kb limit has become a limiting factor on the development of PCs. Many methods have been tried to find a way around the memory limit to allow larger programs to be run.

7.1. Expanded and Extended Memory

The original CPU on the PC, the 8086, is only capable of addressing, or accessing, up to 1Mb (1024Kb) of memory. The top 384Kb of this was set aside for system use, such as the graphics memory, leaving 640Kb for use by the user's programs (in fact the available area will be less than 640Kb, since MS-DOS itself takes up some of this memory). Subsequent processors such as the 80286 are able to address more memory (e.g. 16Mb for the 286) but MS-DOS is unable to access this extra memory.

Early efforts to get round the memory limitations were based on the use of expanded memory. Under the expanded memory method extra memory is paged into the area between 640Kb and 1Mb when required, thus making it accessible by the CPU. Up to 32Mb of RAM can be accessed in this way. It must be noted that the application software must have been written to take advantage of expanded memory. The standard specification for expanded memory is the LIM (Lotus-Intel-Microsoft) EMS (Expanded Memory Specification).

Expanded memory is usually available in the form of plug in cards (see section 10).

Extended memory is a contiguous block of memory from 1Mb upwards. Extended memory is only available to 80286 processors and above. It cannot, however, be accessed directly by MS-DOS programs but various techniques can be used to make it available for programs. For example Windows 3 and some versions of Lotus 123 can use it and extended memory can also be configured to appear like expanded memory. In all cases the software application needs to have been specially written to take advantage.

7.2. Memory Caching

Memory caching works on the same principle as disk caching. The rate of data transfer to and from system memory is limited by the speed of the RAM chips used. Unfortunately high speed memory chips cost more than lower speed memory chips. To increase the rate of data transfer to and from the CPU and the RAM a cache of high speed memory is used. The cache controller works out which block of memory is the most commonly used and transfers its contents into the cache.

The 80486 processor has an in-built memory cache. Some of the more expensive 80386 based PCs come with cache memory and controllers.

7.3. RAM Disks

A RAM disk is a block of system memory which is made to appear like an extra disk drive. Since transferring data to and from memory is much faster than transferring data to and from disk, RAM drives are very fast. RAM drives are normally located in the area between 640Kb and 1Mb. Note that the contents of a RAM drive is lost when the PC is switched off.

7.4. Virtual Memory

Virtual memory can be regarded as the inverse of RAM disks. With virtual memory hard disk space is made to appear like system memory, thus increasing the amount of memory available for programs. This technique is used by Windows 3.

7.5. DOS 5

As stated earlier not all of the base 640Kb memory is available to the user, since part of it is taken up by MS- DOS and device drivers. (A device driver is a piece of software which allows the PC to communicate with or `drive' a particular hardware device such as a mouse).

The latest version of MS-DOS, version 5.0, has a feature allowing some of this memory area to be freed by allowing most of the operating system and device drivers to be loaded in some of the unused area between 640Kb and 1Mb. Thus more memory is free for application programs.

8. Printers and Plotters

A printer may be connected to one of the serial or, more commonly, parallel ports of a PC. The availability of a printer is especially important for applications such as word processing. Printers vary enormously in quality and speed of output.

8.1. Printer Types

Printers can be grouped by the method with which they print.

8.1.1. Dot-Matrix Printers

The most common type of printers are dot-matrix. This refers to the way ink is applied to the paper - by a set of pins impacting onto the paper through an inked ribbon to form each character. Printer quality depends on the number of pins on the printer head. This is usually 9 pins, but 24 pin printers are available with a corresponding increase in print quality (and cost).

Most dot-matrix printers have NLQ (Near Letter Quality) options where higher quality output is produced at a lower print speed.

The standard for dot-matrix printers is Epson and virtually all dot-matrix printers claim Epson compatibility.

8.1.2. Daisywheel Printers

Daisywheel printers were the first printers to produce letter quality (LQ) output; their operation being similar to that of typewriters. They are limited by the fact that they can only produce characters that exist on the daisywheel and cannot produce graphical output, only text.

Daisywheel printers have been made virtually obsolete by the wide availability of cheap laser printers and inkjet printers.

8.1.3. Laser Printers

Laser printers have the advantage of being able to produce letter quality text as well as high quality graphics. Their disadvantage is that they are expensive to buy and run; although costs are coming down.

Laser printer quality is measured in dots per inch, the most common being 300 dpi. They are page printers, fan fold paper cannot be used; but one (or sometimes two) automatic paper feed trays are an integral part. Printing speed is usually quoted in pages per minute (ppm).

Laser printers tend to have a larger range of fonts than other printers. A font is a set of characters in a particular typeface. For example this document has been producing using Times Roman with section headings in Helvetica.

The Hewlett Packard Laserjet series is a fairly common standard, many laser printers emulating it.

The printer's in-built memory can usually be increased to allow the use of downloadable (or soft) fonts. These are fonts which are stored on disk and transferred to the printer's memory when required.

Some laser printers (e.g. Hewlett Packard) use font cartridges which can be plugged into the printer to increase the number of fonts available.

Postscript Printers are a type of laser printer offering more flexibility, in terms of fonts and font sizes, than normal laser printers. They are, however, considerably more expensive. Postscript is a page description language rather than a hardware standard.

8.1.4. Inkjet Printers

Inkjet printers work by spraying a fine jet of ink on the paper to form the characters or graphic. Inkjet printers produce high quality output, near to that produced by laser printers, and are quiet in operation. Examples include the Hewlett Packard DeskJet.

8.2. Interfacing Printers

Printers are connected via a port at the back of the PC. This is usually the parallel output port (25 pin female) although a few printers use the serial interface. Serial interfaces are considerably slower.

A printer can be shared between a number of PCs using a switching box (either manual or automatic).

8.3. Using a Printer

It is advisable to switch on the printer (and any other peripherals) before switching on the PC.

Make sure that the printer you intend using is supported by your software package. Most software packages, on installation, provide a list of printer models from which to choose. If your particular printer is not catered for select an Epson printer if you have a dot-matrix; or a Laserjet printer if you have a laser printer.

8.4. Plotters

A pen plotter is an output device essential for graphical applications like Computer Aided Design (CAD). Plotters provide a better quality graphics output than printers and allow the use of different colours (high quality colour printers are available, but very expensive).

Your application package will translate your graphic into plotter instructions. The Hewlett Packard Graphic Language (HPGL) provides the standard for output to plotters, and the majority of plotters will accept HPGL output.

Plotters can be interfaced to a PC by a parallel or serial link (although serial connection is more common than for printers, since the parallel port is usually taken up by any printer attached).

Plotters come in various configurations, varying in number of pens available (usually 4 or 8; one for each colour) and size (A4,A3 etc).

Common manufacturers include Hewlett Packard and Roland.

9. Maths Co-processors

A Maths Co-processor (or Floating Point Unit, FPU) is an optional chip that can speed up the execution of your software considerably. Floating point operations such as decimals and logarithms can take many instruction steps on the main processor. Such calculations can be handled more efficiently if passed on to a co-processor.

Therefore, if your software requires many maths calculations (e.g. Spreadsheets, CAD) the installation of a co-processor will be advantageous and in some cases a necessity. The increase in speed can be as much as a factor of five. On the other hand some applications such as word-processing will benefit little or not at all from the installation of a co-processor.

Co-processors can be included as an option on purchase of a PC or installed at a later date. The slot for the co-processor resides on the motherboard, close to the CPU. Installation is a straightforward process.

It is important to note that application software needs to have been written with a co-processor in mind, otherwise there will be no advantage at all in having a maths co-processor installed. Most software written for use with co-processors will check whether one is installed.

Some software packages will not work, or will run very slowly, unless a co-processor is installed.

9.1. Selecting the Correct Co-processor

Co-processors have to be matched to the main processor. They are numbered in a similar manner to main processors (see table 3). The clock speed of the co-processor also has to be matched with that of the main processor (the exception is the 80287 co-processor which need not match the main processor in speed). For example, a PC with a 20MHz 80386 processor will require a 80387 co-processor running at a speed of 20Mhz.

Table 3 Selecting the Correct Co-processor

Note that the 80486 processor has an in-built maths co-processor.

10. Expansion Slots

To allow extra features to be added, most PCs have expansion slots. These slots allow the insertion of expansion cards. Data is transferred to and from expansion cards via electronic tracks called the bus.

The bus is analogous to a motorway - the more tracks on a bus the faster data can be transferred. For example, a bus 32 tracks (lanes) wide can carry twice as much data as a bus 16 tracks wide. A bus 16 tracks wide is known as a 16 bit bus i.e. 16 bits of data can be carried down the bus simultaneously. The number and width of slots vary from PC to PC. To save space some PCs will have fewer expansion slots, thus allowing a smaller system box.

Usually the disk controller (the circuitry which controls the disk drives), graphics adapter and serial and parallel ports are located on cards, thus reducing the number of slots available for other purposes. Common uses for expansion slots are networking cards (e.g. Ethernet), digital/analogue converters and FAX cards. Expansion cards also allow extra RAM to be added to the PC.

Putting graphics adapters and disk controllers on cards allows the PC to be easily modified and upgraded.

10.1. The Bus

As mentioned earlier data is transferred to and from cards via the system bus. There are four main types of bus, varying in width and speed of data transfer.

The original PC bus (found on XT machines) is only eight data bits wide, so data can be transferred in blocks of eight bits.

The AT bus, which was introduced with the AT PC, is sixteen bits wide and operates at a higher speed than the PC bus. Thus data transfer rates are much higher. The AT bus is also found on 386 PCs and remains the most common.

The Micro Channel Architecture (MCA) bus was introduced by IBM in their PS/2 PCs. It is 32 bits wide and faster than the AT bus, as well as having other features. Few PCs have an MCA bus. It is incompatible with previous buses and MCA cards will not work in other systems.

The Extended Industry Standard Architecture (EISA) bus is, like MCA, a 32 bit bus but is compatible with existing AT expansion cards. Currently few PCs have an EISA bus.

The majority of PCs have a mixture of 16 bit and 8 bit expansion slots.

11. Mice, Digitizers, and Scanners

This section covers alternatives to the keyboard for inputting information and instructions to the PC.

11.1. The Mouse

A mouse is a device which moves a pointer around the screen, options being selected by pressing (or `clicking') a mouse button.

More and more software is being written incorporating menus. An option on a menu being selected by moving the mouse cursor over the option and clicking on it. With some software such as CAD a mouse is essential. Graphical User Interfaces, such as Windows and GEM, in practice also require the use of a mouse.

A mouse is normally linked to a PC via the mouse port. The standard for the mouse is the Microsoft Bus Mouse. Another common type of mouse is the serial mouse which connects to one of the serial ports in the PC. Normally software called a mouse driver has to be loaded into memory before the mouse can be used. Generally mice have two buttons but three button mice are also available. If you have software which requires the third, centre, button to be pressed, this can be achieved by pressing both buttons simultaneously.

11.2. Digitizers

A digitizer (or graphics tablet) is an input device, used in Computer Aided Design for reading a paper drawing into a CAD package; in effect by tracing the drawing. As well as digitizing drawings, digitizers can be used as a replacement for a mouse. Digitizers come in sizes from A4 to A0 size.

11.3. Scanners

Scanners allow you to convert an image on paper into a bitmap file. The image can then be displayed on the PC and used in applications such as Desk Top Publishing. It is also possible to run Optical Character Recognition software in conjunction with a scanner and read in printed text into the PC. For example an abstract can be scanned and imported into a word processor for further manipulation. Scanners can be either flatbed or hand-held.

12. The Keyboard

This section covers the use of the keyboard.

12.1. Layout of the Keyboard

There are two styles of keyboard in common use, the older 84-key and the now more common 102-key expanded keyboard. The 102-key keyboard normally consists of four main parts;

A typewriter-style alphanumeric keyboard with four extra keys labelled Esc (Escape), Ctrl (Control), and Alt (Alternate).

A numeric keypad, situated at the far right of the keyboard, providing the digits 0 to 9, a decimal point and plus and minus signs, together with four special keys labelled Num Lock (Number Lock), Scroll Lock, Ins (Insert) and Del (Delete). On the 84-key keyboard the numeric keys are also used as cursor control keys.

In between the alphabetic keys and the numeric keypad there are two groups of keys. The top group repeats the functions on the numeric keypad. Below there are four cursor keys. These are not present on the 84-key keyboard.

A set of twelve function keys situated in a single row above the main typewriter keyboard and labelled F1 to F12. On the 84-key keyboards there are ten function keys situated to the left of the main typewriter keys.

The layout of these keys is shown in figure 6 and their general uses are described in the following sections. The position of some of the keys may be different from that described below.

In order to save space, the keyboards on portable and notebooks PCs have largely different layouts from that described above.

Figure 5 102 Key Keyboard Layout

12.2. Capital Letters and Punctuation Marks

As with a typewriter, to type upper case (capital) letters, or to obtain a punctuation mark or symbol shown on the upper half of a key, hold down one or other of the two <Shift> keys while pressing the key marked with the required character.

The Shift keys are normally situated on each side of the bottom line of letter keys and are often marked with a `fat' up-arrow). To type text in capital letters, the keyboard can be `locked' into capitals by pressing the Caps-Lock key (the key or a sign on the keyboard may be lit). Since Caps Lock only affects the letter keys, it will still be necessary to hold down a Shift key to obtain the punctuation marks and symbols shown on the upper half of keys. To return to lowercase letters, press the Caps-Lock key again (the light will go out). If you press Shift while Caps-Lock is engaged you will revert to lowercase i.e. Shift always reverses the current state of Caps-Lock.

12.3. Numeric Keypad

The numeric keypad at the right of the keyboard can be used for numeric input only if the Num Lock key is pressed (the key or a sign on the keyboard may be lit). To release the numeric keypad and hence use the cursor keys (labelled with arrows), press the Num Lock key again; the light will go out.

On some keyboards the cursor keys are also a separate group of four keys (see figure 6). Either set of cursor keys may be used.

12.4. Screen Control Keys

As well as the four cursor control keys, keys marked PgDn (Page Down), PgUp (Page Up), Home and End are available for cursor movement, depending on the software being used. These keys are also duplicated on the numeric keypad.

12.5. Entering Commands

The key on the right-hand side of the alphanumeric keyboard that is often L-shaped and larger than the other keys, and is labelled with a right-angled, left-pointing arrow ([[??]]) and/or Return or Enter (see figure 6), is used to send a command line to the computer to be processed. After typing in a command to the PC, this key must be pressed to enter or start the command. In general, commands may be entered in upper or lower case letters, or a mixture of the two.

The <Return> key is sometimes known as the <Enter> key. There is also an <Enter> key on the numeric keypad which can be used in exactly the same way as the <Return> key.

12.6. Correcting Typing Mistakes

To correct a mistake that you notice before you have pressed the <Return> key, use the <Backspace> key to `erase' the mistake. The <Backspace> key is situated above the <Return> key and is labelled with a left-pointing arrow.

Each time the <Backspace> key is pressed, the character to the left of the current cursor position is deleted. (The cursor is the flashing underline displayed on the screen.) The correct characters can then be retyped before pressing the <Return> key.

12.7. The Insert Key

The Insert key, sometimes marked INS, acts as a toggle key when entering data or commands. In insert mode any characters entered push into the current line at the cursor position. In overstrike mode any characters entered will overwrite any characters currently displayed.

12.8. Other Useful Keys

The operation of the Function Keys depends on the particular software being used. For example pressing F1 on a lot of software packages calls up a help screen.

The ESC key usually allows you to `escape' from a particular environment.

The Print Screen key, sometimes marked PrtSc, when pressed in conjunction with the Shift key copies the screen image to the printer.

The Alt and Control keys are used in combination with other keys to execute particular commands depending on the software being used. For example Control-F2 will initiate a spell check when using WordPerfect.

Part B - Using the PC

13. What Is MS-DOS?

MS-DOS stands for MicroSoft Disk Operating System.

MS-DOS is the software underlying a series of commands that will allow programs to be run, files holding information to be created and managed, and disks to be written to and read from. MS-DOS is loaded from a disk, known as a system disk, when the PC is switched on.

13.1. Internal and External MS-DOS Commands

It is important to appreciate from the start, and in particular when using MS-DOS from a floppy disk, that there are two types of MS-DOS commands, internal (or resident) and external (or transient).

Internal commands are loaded and held in the computer's memory when MS-DOS is started up and can thus be executed immediately when required even if the system disk is no longer available. Examples of internal commands are: COPY, DEL, DIR, REN and TYPE. Internal commands are held in a file called COMMAND.COM.

External commands are not loaded into the computer's memory when MS-DOS is started up and are read from the disk only when required. This means that a command of this type will fail on a floppy disk system unless the MS-DOS system disk is in the current disk drive at the time that the command is issued; otherwise the appropriate drive name and path should precede the command name (see section 20.1).

If an MS-DOS disk is not available or the path to the MS- DOS directory has not been specified when a external command is issued, there will be an error message of the form,

Bad command or filename

Examples of external commands are: DISKCOPY, FORMAT and PRINT.

Note: In the following sections,

(1) Characters typed by you are in ITALIC CAPITALS

(2) Text displayed on the PC screen is in bold

(3) Keys to press are enclosed by < > e.g. <F2>

(4) <Control/Z> means hold down Control key and press Z

(5) Return and Enter are one and the same. Every command entered should be followed by a Return key press.

14. The Start Up Procedure

Start up, or boot up as it is often called, is the process of readying the hardware and software for use. The disk with the MS-DOS system files on it is often referred to as a bootable disk since this disk can be used to start up the system. The term `booting' the system comes from the saying `pulling oneself up by one's bootstraps'.

Startup is performed each time the computer is switched on. The startup procedure copies the internal operating system commands into the PC's memory, where they will remain until the system is restarted or switched off. Startup has been successful when the system prompt (the disk drive name) is displayed on the screen.

14.1. Starting Up MS-DOS

To start up MS-DOS on a PC with a hard disk take the following steps;

(l) Check that there is no floppy disk in the floppy disk drive.

(2) If the display screen is not already on (check the light which is normally below the screen), turn it on. Also turn on any peripherals such as printers.

Turn the PC on. Nothing will appear to happen for a few seconds while the PC performs a `self check' of its internal components, such as system memory, and reports any problems. It does this whenever it is first turned on.

The light on the front of drive C, the hard disk, will come on and the drive motor will start running as the internal part of MS-DOS is read into the computer's memory.

(3) Once the internal portion of MS-DOS has been loaded, the system may prompt on the screen for today's date. The prompt takes the following form,

Current date is Tue 01-06-1991

Enter new date (dd-mm-yy):

Pressing <Return> will leave the date unchanged. Alternatively enter the new date in the form mm-dd-yy (i.e. month-day-year, two digits for each e.g. 08:12:90) or it may be in the form dd-mm-yy, check the format before entering the correct date. After typing in the date, press the <Return> key.

(4) The current time may then be requested. The prompt takes the following form,

Current time is 9:03:39.75

Enter new time:

Type the time using the 24-hour clock in the format hh:mm (e.g. 9:15, or 15:03). If the exact time is not known, enter a reasonable estimate or just press the <Return> key to accept the time offered.

It is advisable to check the date and time, as these are recorded in the file directory when files are created or amended.

Note: a lot of PCs now have battery powered clocks which keep a record of the date and time even when the PC is switched off.

(5) After displaying information about the version of MS- DOS being used the MS- DOS prompt C> will appear on the screen. The PC is awaiting instructions. Enter an MS-DOS command or the name of the program to be used.

On booting-up the PC will search the A drive first for a system disk; if none is found it will then check the hard disk. Thus hard disk systems can be booted-up from a floppy disk by inserting a system disk in drive A and following the instructions above. The system will then load from drive A rather than drive C.

To boot up a PC with twin floppy drives and no hard disk, insert a system disk in drive A before switching on.

Note : A system disk, either hard or floppy contains a minimum of three files, two of which are hidden. It is not enough that the files exist on a disk to make that disk a system disk; the disk has to be formatted as a system disk (see section 15.1).

14.2. Restarting MS-DOS

There are occasions when it may be necessary to stop what is currently running on the PC and return to the MS-DOS prompt.

In general, if an application program is running, such as WordPerfect or dBase IV, there will be a `proper' way to leave the program by selecting the appropriate Quit, Stop or Exit command. This `proper' way of getting back to MS-DOS should always be used as the program will have been designed to close any open files, delete workfiles it has created, etc., on receiving the `Quit' command.

However, if all else fails, MS-DOS may be restarted. On a hard disk system first check that there is no disk in drive A. Hold down the <Ctrl> and <Alt> keys and, while holding them down, press the <Del> key that is situated at the bottom of the numeric keypad. This is known as a `soft reset' or `warm boot/start-up' as it reloads the MS-DOS software and resets the computer to its start-up state. The difference between this and a `hard reset' or `cold boot/start-up' (turning the PC off and then on again) is that it is quicker as there is no hardware check.

Most PCs have a RESET button on the front of the main unit which when pressed performs a soft boot.

Warning: The contents of RAM are lost when a PC is rebooted.

15. MS-DOS and Disks

15.1. Formatting Floppy Disks

Before floppy disks can be used they have to be formatted for use. This is done using the external MS-DOS command, FORMAT. The command issued will depend on disk size and capacity.

Warning

Formatting a disk will erase any information currently stored on the disk. So take care.

The following commands assume the disk to be formatted is in drive A.

Formatting 51/4" Floppy Disks

To format a double density disk in a double density drive, or a high density disk in a high density drive, use

FORMAT A:

To format a double density 51/4" disk in a high density (1.2Mb) drive, use

FORMAT A: /4

This will give the disk a capacity of 360Kb.

Formatting 31/2" Floppy Disks

To format a double density disk in a double density drive, or a high density disk in a high density drive, use

FORMAT A:

To format a double density 31/2" disk on a high density (1.44Mb) drive

FORMAT A: /T:80 /N:9

This will give the disk a capacity of 720Kb.

Warning

Do not format high density 51/4" disks to 360Kb, or double density 51/4" disks to 1.2Mb. This rule also applies to 31/2" disks.

To format a floppy disk as a bootable system disk use the /S option. For example

FORMAT B: /S

will format the floppy in drive B as a system disk.

Do not type FORMAT C: unless you want to destroy all the information on your hard disk!

15.2. Copying Floppy Disks

Copies of floppy disks can be made by using the external command, DISKCOPY. Both disks need to be of the same size and capacity. Your PC need not have two identical floppy drives for diskcopy to work; for example, to copy a disk in drive A use

DISKCOPY A: A:

and follow the on-screen instructions.

The disk to which you are copying need not have been previously formatted.

Warning

Any information stored on the disk to which you are copying will be erased.

You are strongly recommended to write protect the source disk when using diskcopy to avoid accidental overwriting.

15.3. Checking Disks

The external command CHKDSK will scan the specified disk, checking for errors such as bad sectors. For example

CHKDSK C:

will check all the files on drive C for errors. To fix any errors use the /F switch. For example

CHKDSK C: /F

As well as checking for errors, CHKDSK will give useful information on disk space usage.

16. Files and Filenames

16.1. Files

Information stored on a disk (floppy or hard) is organised into units known as files. A file may contain, for example, a program, a set of data, or a document. Each file must be distinguished by being given a filename. Files can be grouped together in directories.

16.2. Filenames

Filenames are chosen by the user, subject to the following rules,

(1) The length must be from 1 to 8 characters, with no spaces.

(2) The characters must be drawn from the letters A to Z, the digits 0 to 9, and the additional characters - : $ & ! % ( ) { } ' " _ @

For example,

MY_DOC_2 1986DATA %TOTALS rubbish Club(86)

are valid filenames. Filenames may be referred to in upper or lower case; they are always translated into upper case. Choose filenames that are meaningful, i.e. descriptive in some way of the file's contents.

16.3. File Extensions

Optionally, a filename may be followed by a file extension. This consists of from one to three characters and is separated from the filename by a full stop or `dot'. The purpose of a file extension is to describe the kind of information held in the file. In many cases they are added automatically by an application program. For example,

REPORT.DOC for textual data;

TOTALS.WKS could be for a Lotus 1-2-3 worksheet.

The following are some of the commonly used file extensions,

BAS BASIC source file

BAT Batch file

COM Command binary file

DOC Used by many word processors (to mean document)

EXE Executable binary file

FOR FORTRAN source file

SYS System file

Extensions BAT, COM, EXE and SYS are meaningful to the MS- DOS operating system and should not be used for general data files. The others are used as a matter of convention. If the software does not require specified file extensions to be used, personal extensions may be devised as an extra aid to identifying the contents of files.

If a file has a file extension, this must be included when using the filename with an MS-DOS command. For example

C> TYPE REPORT.DOC

will display the contents of the file called REPORT.DOC on the screen.

16.4. File Specifications

If the file is not held on the disk in the current drive it will also be necessary to specify which disk drive contains the disk on which the file is stored. This is done by adding the drive specifier (A: or C:) to the front of the filename.

The description of a file, known as a file specification, is therefore,

<drive letter>:<filename>.<file extension>

For example,

C:PROJECT.DOC

A:TOTALS.BAS

Note: Files in the same disk directory must have unique file specifications. They may have the same filename provided that they have different file extensions. For example, TOTALS.BAS and TOTALS.DAT may exist in the same disk directory.

16.5. Wildcard Characters

It is often convenient to give a file specification which corresponds to a group of files, rather than a single file. This is done by using so-called wildcard characters. The asterisk ,*, is a wildcard character and can be used to represent any number of arbitrary characters (including none) in the filename or file extension. For example

*.DOC refers to all files with an extension of DOC.

FILEA.* refers to all files with the filename FILEA and any file extension, for example FILEA.DAT, FILEA.TXT.

TEST*.TXT refers to all filenames beginning TEST, and with the extension TXT, for example TEST.TXT, TESTNEW.TXT, TEST1.TXT.

Note that no characters should follow the * in either the filename or extension. For example, *T.DOC will be treated as *.DOC.

A second wildcard character, a question mark ,?, is taken to represent any single character in a filename or file extension. For example

TEST?.TXT refers to TESTl.TXT, TESTA.TXT etc., but not TEST.TXT or TESTNEW.TXT.

PROG.P?? refers to PROG.PAS, PROG.PRG, etc., but not PROG.PG or PROG.P.

DATA???.TXT refers to DATANEW.TXT, DATAOLD.TXT etc., but not DATA1.TXT.

Note: Not all commands can make use of wildcards.

16.6. Directories

Files are held in directories on a disk. Initially each disk has one directory (called the root directory), but sub-directories may be created. Directories allow files, especially on hard disks, to be kept together in logically related groups. For example, in a filing cabinet all letters would be kept together, accounts information would be together and so would minutes of meetings. On the computer a similar system can be arranged using directories; files of letters would be in one directory, accounts information in a second and minutes of meetings in a third. Full details about directories; how to create them, access files in them and delete them are given in section 21.

17. MS-DOS Commands

This section covers the commands,

DIR Listing a directory contents.

TYPE Displaying the contents of a file on the screen.

PRINT Listing the contents of a file on the printer.

COPY Copying files.

REN Renaming files.

DEL Deleting files.

17.1. Listing the Contents of a Directory

The MS-DOS command DIR (DIRectory) gives a list of the filenames in the current directory. Where there are no user sub-directories on a disk the DIR command will list every file on the disk.

Hard disks generally have more than one directory and the listing of other directories can be done either by changing the current directory or specifying the directory.

To obtain details of the files on a disk in the current directory, type

C> DIR

Volume in drive C is DISK_VOL1

Directory of C:\

COMMAND COM 25276 24-07-87 12:00a

CONFIG SYS 202 21-03-90 10:45a

AUTOEXEC BAT 1024 21-03-90 10:50a

WP51 <DIR> 12-04-90 11:34a

LOTUS <DIR> 12-04-90 2:33p

LETTERS <DIR> 13-04-90 11:22a

6 File(s) 36345210 bytes free

The directory listing produced by the DIR command shows the name and size of each file in bytes (equivalent to characters, in the case of text files), and the date and time when the file was created or last altered. The <DIR> after some of the names indicates that these are sub-directories which may also contain files. At the beginning of the listing the disk drive is specified and whether it is labelled. Disks can be labelled when they are formatted, users are recommended to do this. At the end of the listing, the total number of files in the current directory and the amount of space still free on the disk are given.

To obtain details of the files on the disk in drive A, type

C> DIR A:

To obtain details of the file REPORT.DOC on the disk in drive A, type

C> DIR A:REPORT.DOC

Alternatively the current disk drive can first be changed to A and then the DIR listing done

C> A:

A> DIR REPORT.DOC

To obtain details of a group of files, the wildcard technique described in section 16.5 may be used. For example

C> DIR C:*.DOC

would give details of all the files in the current directory on the disk in drive C that have the file extension DOC (the C: could have been omitted in this example since it is referring to the directory on the current drive).

If there are many files within a directory and the list scrolls off the top of the screen when the DIR command is issued, using the /W parameter will condense the display into a multi-column listing.

C> DIR/W

A multicolumn listing includes only the filenames and their extensions, and the total number of files in the current directory and the free space on the disk. The date and time of creation or modification and the size of the files are omitted.

Alternatively, the command

C> DIR/P

gives a list of the files in the current directory which stops after 23 filenames are displayed, with the prompt

Strike a key when ready...

Striking any key will give the next 23 filenames, and so on, until the end of the directory listing.

If there is a printer attached then the command

C> DIR > PRN

will list the contents of the current directory on the printer. In this context the `>' is known as the redirection symbol, that is, the output to the screen is redirected to the printer.

Alternatively, giving the DIR command followed by <Shift/PrtScr> will print the currently displayed screen.

For more information on sub-directories and how to create them see section 21.

17.2. Displaying and Printing the Contents of a File

The command TYPE is used to display the contents of a file on the screen. The external command PRINT will print files on a printer connected to the PC. For example

C> TYPE FILEA.DOC

will list on the screen the contents of FILEA.DOC. If a file on the disk in drive A is required then it can be displayed using the command

C> TYPE A:FILEB.DOC

Alternatively the current disk drive can first be changed to A and then the listing requested.

C> A:

A> TYPE FILEB.DOC

The command PRINT should be used only on a PC with an attached printer. For example

C> PRINT LETTER.TXT

Files can also be printed using redirection. For example

C> TYPE FILEB.DOC > PRN

17.3. Copying Files From One Disk to Another

The MS-DOS COPY command can be used to copy (or duplicate) a file or files from one location to another; they may or may not be on the same disk. The command has the format

C> COPY source-file target-file

For example

C> COPY TESTPROG.DAT NEWPROG.DAT

would make a duplicate copy of the file TESTPROG.DAT under the name NEWPROG.DAT in the same disk directory.

Warning

The COPY command will overwrite an existing file of the same name and extension, if such a file is present on the destination disk.

To copy from one disk drive to another, the disk drive name must also be included. For example

C> COPY MYREPORT.DOC A:

would copy the file MYREPORT.DOC in the current directory on drive C onto the disk in drive A. In this case, the omission of a filename on drive A means that the file would have the same name on A.

To copy to a file on another drive and change the name, specify a new filename in the target file specification. For example

C> COPY CURRENT.DAT A:OLD.DAT

would copy the file CURRENT.DAT in the current directory on drive C into a file called OLD.DAT on the disk in drive A.

To copy a group of files from one disk to another, the wildcard character may be included in place of all or part of the filename and/or the file extension. For example,

C> COPY *.DOC A:

will copy all files with the file extension DOC in the current directory on drive C into the current directory on the disk in drive A, all the filenames will be the same as the source filenames. Similarly

C> COPY *.* A:

will copy all the files in the current directory on drive C onto the current directory of the disk in drive A.

Files can be copied in the opposite direction, i.e. from drive A to the current directory on drive C. For example

C> COPY A:NEWDOC.TXT

would copy the file NEWDOC.TXT from the disk in drive A into the current directory on drive C and it will have the same name. Alternatively the current disk drive can first be changed and then the file copied,

C> A:

A> COPY NEWDOC.TXT C:

In this case the target disk drive must be included.

To copy all the files with a file extension of TXT in drive A to the current directory on drive C and change their extensions to DOC,

C> COPY A:*.TXT *.DOC

Since the current drive is C the drive name is not necessary before the target filename. Similarly

C> COPY A:*.*

will copy all the files in the current directory of the disk in drive A into the current directory on drive C.

The copy command can also be used to print files. For example

C> COPY NEWDOC.TXT PRN

will print the file NEWDOC.TXT on an attached printer.

17.4. Renaming Files

The RENAME command (or its abbreviation REN) is used to change the name of a file, for example

C> RENAME FILEA.TXT LETTER.TXT

will rename the file FILEA.TXT in the current directory on drive C. The name FILEA.TXT will be removed and a directory listing would show the existence of a file called LETTER.TXT.

To rename a file not on the current disk drive, you must include the drive name as part of the existing file specification, for example

C> REN A:FILEA.TXT LETTER.*

will rename FILEA.TXT on drive A to LETTER.TXT on drive A. Since the file extension is not changing the wildcard character is used in the target file extension.

Alternatively the default drive may first be changed to A and then the file renamed without specifying the drive name in the file specification,

C> A:

A> REN FILEA.TXT LETTER.*

To RENAME a group of files the wildcard character can be used, for example

C> REN *.DOC *.OLD

will rename all the files with an extension of DOC in the current directory and give them an extension of OLD.

RENAME will not overwrite an existing file of the same name. If the filename already exists the following message will be displayed,

Duplicate file name or file not found

Note that this contrasts with the COPY command which gives no warning when a duplicate file exists and overwrites the file.

17.5. Deleting Files

The DEL command is used to delete files. The command

C> DEL TEXT1.DOC

will delete the file TEXT1.DOC from the current directory on drive C.

C> DEL A:*.TXT

will erase all the files in the current directory on drive A with an extension of TXT.

C> DEL TEST*.*

will delete any files in the current directory on drive C with filenames beginning TEST and any file extension, such as TEST10.DAT, TESTNEW.TXT, etc.

Beware of the command DEL *.* which will delete all the files in the current directory! (MS-DOS asks you to confirm whether you really want to delete all the files after this command is issued.) Do not delete any files called . or .. (these filenames refer to the current and parent directories; see section 21.2). Do not delete the files called ANSI.SYS, CONFIG.SYS, AUTOEXEC.BAT, and COMMAND.COM.

17.6. Programs

All the external commands covered so far, such as PRINT, have file extensions of either EXE or COM. Any file with such an extension is a program and can be executed simply by typing its filename, assuming the file is in the current directory or in a directory contained in the path. Such a file contains data understandable only by the PC and not you and cannot be PRINTed or TYPEd. Program files can be grouped into external DOS commands, programs written by yourself and compiled, and application packages, such as WordPerfect, written by others. Application packages are discussed later.

18. Controlling the Screen

18.1. Clearing the Screen

To clear the screen type CLS (CLear Screen) in response to the MS-DOS system prompt. The screen will clear and the system prompt will be displayed on the top line of a blank screen.

18.2. Stopping the Screen from Scrolling

When information is being displayed on the PC's screen, each new line of text is displayed under the previous one until all possible lines on the screen (24) have been used. All the lines of text are then moved up one line so that the top line disappears from the top of the screen, and room is made at the bottom of the screen for another line. This action is known as scrolling. To stop the screen scrolling and thus make it pause, hold down <Ctrl> and press <S> at the same time. To restart the scrolling, press any key (or <Ctrl/S> again). Alternatively press <Break> and any key to restart scrolling. This is useful if you are displaying a particularly large file or a long directory listing.

Alternatively for listing long files you can use the MORE command. For example,

C> TYPE LONGFILE.DAT | MORE

which works in the same way as the /P switch on the DIR command. The | symbol is normally obtained by pressing <Shift> and \.

18.3. Abandoning Commands

To interrupt the action of any MS-DOS command, such as displaying the contents of a file, press <Ctrl/C>. The MS- DOS system prompt will be displayed. <Ctrl/Break> sometimes works when <Ctrl/C> does not.

18.4. Command Line Editing

If a mistake is made when typing a command and <Return> has not been pressed, the error may be corrected using the <Backspace> key to delete the characters back to the mistake and then retype.

When a command line is entered it is held in a buffer (an area of memory) until <Return> is pressed when it is transferred to another area called the template. Therefore the template holds the previous command. It is possible to retrieve the previous command line from the template by pressing the function key marked <F3>.

19. Ending a Session on the PC

After using an application program, wherever possible leave the program by means of the appropriate Quit, Exit or Stop command and return to the MS-DOS prompt before turning off the PC.

Once the MS-DOS system prompt is displaying on the screen, switch off as follows,

(l) Remove any floppy disks from the disk drives and place them in their envelopes.

(2) On a hard disk system it is recommended that the read- heads on the hard disk are parked. The command to do this varies with manufacturer (consult the manual provided with your PC), common variations are PARK, DPARK and FXPARK. The disk park command must be used before a hard disk system is moved to another location. Some hard disks have automatic disk parking.

(3) Turn off the PC by putting the power switch on the main unit into the off position.

(4) Turn off the monitor screen and any peripherals.

(5) Turn off at the mains.

20. More About Directories

Directories allow files to be kept together in logically related groups. For example, files of letters could be kept in one directory, accounts information in a second, and minutes of meetings in a third. This section covers the concepts of directories, their creation and manipulation, and the copying of files between directories.

Directories are of more value on a hard disk system than on a system using only floppy disks; because of the greater size of a hard disk it is more important to keep the data on it in an organised fashion. Normally, on a system using floppy disks, a separate disk is used for each project although it is possible to have sub-directories on a floppy disk.

The organisation of the directory structure is based on the concept of a tree. As with a tree it has a root. This root is the foundation of the directory structure and all other directories in the system.

When a disk is formatted, the root directory is created automatically; it cannot be deleted. The root directory is the default directory on start-up from either a floppy disk or a hard disk. Named directories can then be created beneath this root directory and further directories beneath these directories. The following diagram shows how directories in such a hierarchy relate to each other.

The root directory has the special name \

In the above diagram, the root directory contains a number of files as well as the three directories ACCOUNTS, SUE, and WP. The directory ACCOUNTS contains a number of files, the directory SUE contains two sub-directories, DOCS and LETTERS, as well as some files, and the directory WP contains some files. A directory which contains one or more sub-directories is called the parent directory of those sub-directories. In the above example SUE is the parent directory of DOCS and LETTERS, and the root is the parent directory of ACCOUNTS, SUE and WP. The terms directory and sub-directory are used more or less interchangeably.

Directory names follow the same rules as do filenames but do not normally include an extension, though this is allowed.

The number of files and/or directories in the root directory is limited to 111 on a 360 KB floppy disk and 512 on a 20 Mbyte hard disk, but there is no such limit within sub-directories. Users are recommended not to have too many files in any directory as they will become difficult to manage.

You are recommended only to store a minimum of files in the root directory of the hard disk. Typically the root directory will contain only the files AUTOEXEC.BAT and CONFIG.SYS (the relevance of these two files are discussed later). All files relating to the operating system (for example external DOS commands) are normally stored in a directory called DOS.

20.1. Pathnames

The pathname of a given file is the route which must be traversed from the root directory to reach the directory in which the file resides. For example, in the above diagram, the path to a file in the directory ACCOUNTS is the pathname

C:\ACCOUNTS

The \ before ACCOUNTS refers to the root directory. The pathname to a file in the directory LETTERS under the directory SUE is

C:\SUE\LETTERS

In this example the initial \ refers to the path starting at the root directory and the second is a separator between directory names on the path. If there is a file called MAR88.TXT in the directory ACCOUNTS then the pathname plus filename is

C:\ACCOUNTS\MAR88.TXT

Again the initial \ refers to the root directory and this time the second \ is the separator between the directory name and the filename.

A full file specification includes the drive name, pathname, filename and extension. If the file is on the hard disk, i.e. drive C, then the full file specification would be

C:\ACCOUNTS\MAR88.TXT

In the above diagram of a directory structure, if there is a file called AUG10.CB in the directory LETTERS under SUE then the full file specification would be

C:\SUE\LETTERS\AUG10.CB

Files in different directories on the same drive can have the same filename, but they will have different file specifications owing to the different pathnames. For example, a file called MAR88.TXT in the directory DOCS under SUE will have the file specification

C:\SUE\DOCS\MAR88.TXT

and will be distinguished by MS-DOS from the file with the same filename in the directory ACCOUNTS which would have the file specification

C:\ACCOUNTS\MAR88.TXT

Files within the same directory must, of course, have different combinations of filename and extension.

In the above examples of pathnames the initial \ refers to the root directory and subsequent ones are the separators between directory names in the path. A \ is then used to separate the filename from its directory name. A pathname not preceded by a \ is taken to be a relative pathname from the current directory. Examples of relative pathnames are given in section 21.4.

All of the file handling commands can be used to manipulate files not in the default (current) directory by giving the pathname or the full filename specification. In the examples below, since the default drive is C, the drive specification (C:) may be omitted.

(1) To display on the screen the file DATAl.DAT in the directory ACCOUNTS,

C> TYPE C:\ACCOUNTS\DATA1.DAT

(2) To obtain a directory listing of the files in the sub-directory WP,

C> DIR C:\WP

(3) To obtain a directory listing of the files in the directory DOCS under the directory SUE,

C> DIR C:\SUE\DOCS

(4) To list on the screen the file called AUG10.CB in the sub-directory LETTERS,

C> TYPE C:\SUE\LETTERS\AUG10.CB

In section 21.2 details are given of how to change the current directory so that the full file specification does not always have to be used.

20.2. System Prompts

By default the system prompt is the name of the current drive followed by an angle bracket. On a hard disk system this will normally be C> and on a floppy disk system this will normally be A>. It is possible to change the default disk drive by typing the new drive name (followed by :). For example

C> A:

A>

To change the current drive back again to C, type C: followed by <RETURN>.

The prompt A> appears when MS-DOS is first loaded from a floppy disk to indicate that drive A is the current drive. This means that MS-DOS will expect to find the programs required on the disk loaded in drive A unless you tell it otherwise.

On a PC with two floppy drives to change the current disk drive to drive B, simply type B: and <Return>. The MS-DOS prompt will then change to B>. For example

C> B:

B>

To change the current drive back again to drive C, type C: followed by <Return>. It is also possible to change the default directory from the root to a sub-directory (see section 21.2). If this is to be done it is useful if the system prompt indicates which directory you are currently using. The PROMPT command can be used to make the system prompt indicate the current directory. For example

C> PROMPT $P$G

will change the default prompt for the current session. The $P causes the pathname of the current drive name and directory to be displayed as part of the system prompt. The $G causes the greater than character `>' to be displayed after the pathname.

For example

C> PROMPT $P$G

C:\>

When the current directory is changed the prompt will change to indicate the new default directory; in the above case the root directory. If the directory had been changed to ACCOUNTS the prompt would be

C:\ACCOUNTS>

the directory had been changed to LETTERS under SUE the prompt would be

C:\SUE\LETTERS>

The command PROMPT $P$G is often included by users in their AUTOEXEC.BAT file which would make it operate automatically on starting up. The AUTOEXEC.BAT file is a file containing a set of commands which are executed every time the PC is booted. An example of an AUTOEXEC.BAT file including this command is given in section 22.2.

21. Directory Commands

The following sections cover the commands,

MKDIR or MD Creating a directory

CHDIR or CD Change the default directory

RMDIR or RD Deleting a directory

DIR Listing a directory contents

21.1. Creating a Directory

The command MKDIR (or its abbreviation MD) is used to create (Make) a directory. New directories can be created from within the parent directory (or from any other directory as long as the full path to the new directory is given). For example

C:\> MKDIR THESIS

will create the directory THESIS under the current directory which in this case is the root directory. When a directory listing of the root directory is requested, the entry

THESIS <DIR> date time

will be included in the output.

A directory CHAP1 can then be created under THESIS from the root directory using the command

C:\> MD THESIS\CHAP1

The full pathname must be given since the directory is being created from the root directory. It is also possible to change the default directory and then the sub-directory can be created from the new default directory.

21.2. Changing the Default Directory

To change the default directory, the CHDIR (or its abbreviation CD) command is used. To change from the root directory to the newly created directory THESIS type

C:\> CHDIR THESIS

C:\THESIS>

The directory listing of a new directory which has no files in it will show two entries

. <DIR> date time

.. <DIR> date time

where . refers to the current working directory

.. refers to the parent directory

In the above example the current working directory is THESIS and the parent directory is the root directory. The two entries (or pointers) . and .. must not be deleted.

Note If an attempt is made to delete .. the system responds with the question Are you sure (Y/N). A reply of Y will delete all the files in the parent directory!

To change the default directory from the root directory to the directory called LETTERS under SUE,

C:\> CD SUE\LETTERS

C:\SUE\LETTERS>

When moving to a directory below the current directory in the directory hierarchy it is not necessary to give the part of the pathname up to the current directory (i.e. the initial \). For example, to move to the directory LETTERS from the directory SUE which is the parent directory

C:\SUE> CD LETTERS

C:\SUE\LETTERS>

If CD \LETTERS had been specified the system would expect the directory LETTERS to be immediately beneath the root directory and the command would have failed with the message Invalid Directory. Note that changing the default directory on the non-current drive, for example

A:\> CD C:\SUE

A:\>

does not change the default drive; only the default directory.

To return to the root directory from any sub-directory on the default disk drive the command

C:\WP> CD \

C:\>

may be used. This means that to move to a directory on another branch of the tree, for example to move from the directory LETTERS under SUE directly into the directory THESIS, the command would be

C:\SUE\LETTERS> CD \THESIS

C:\THESIS>

To return to the parent directory of any sub-directory the MS-DOS abbreviation .. may be used

C:\SUE\LETTERS> CD ..

C:\SUE>

The \ at the beginning of a pathname always indicates the root directory as the beginning of a search for a directory. For example

C:\ACCOUNTS> CD \SUE\LETTERS

C:\SUE\LETTERS>

will change the default directory to LETTERS. It is a good idea to insert this backslash and specify the path from the root, since the command will then work from any sub-directory.

The command CD on its own displays the name of the current directory.

21.3. Deleting a Directory

The command RMDIR (or its synonym RD) will delete (ReMove) a directory. Before this can be done all the files in the directory must be deleted otherwise the command will fail. If the directory DOCS under SUE is to be deleted then the following steps must be taken

C:\> CD SUE\DOCS

C:\SUE\DOCS> DEL *.*

Having deleted all the files in the directory DOCS (this can be verified by a DIR listing and only the two pointers, . and .., will be left) the default directory must then be changed to the parent directory (SUE),

C:\SUE\DOCS> CD ..

C:\SUE>

The directory DOCS can now be removed.

C:\SUE> RD DOCS

To check that the directory has been deleted issue the following command

C:\SUE> CD DOCS

If the directory has been removed the system will issue the following message

Invalid directory

21.4. Listing the Contents of a Directory

As explained previously, the command DIR lists the names of the files in the current directory. It also gives the names of any sub-directories belonging to the current directory but does not give the filenames of files in the sub-directories. For example

C:\> DIR

would give a list of all the files in the current directory, in this case the root directory. The three sub-directories ACCOUNTS, SUE and WP would be indicated as follows,

ACCOUNTS <DIR> date time

SUE <DIR> date time

WP <DIR> date time

The following examples show the use of the DIR command to list files in different directories (the tree structure on page 81 is assumed to exist).

(l) C:\> DIR

will list the names of all the files in the current directory, in this case the root directory, and the directory names ACCOUNTS, SUE and WP.

(2) C:\> DIR \SUE

will list the names of all the files and sub-directories in the directory SUE. The \ before SUE is not necessary in this context.

(3) C:\> CD SUE

C:\SUE> DIR

will also list the names of the files in the directory SUE. The default directory has been changed to SUE before the directory listing is requested.

(4) C:\> DIR \SUE\DOCS

will list the names of the files in the directory DOCS under SUE under the root directory.

(5) C:\> CD \SUE\DOCS

C:\SUE\DOCS> DIR

will also list the names of the files in the directory DOCS.

(6) C:\SUE\DOCS> DIR ..

will list the names of the files in the parent directory, i.e. SUE, even though the default directory is DOCS.

(7) C:\SUE\DOCS> DIR \

will list the names of the files in the root directory.

(8) C:\SUE\DOCS> DIR \ /W

will give a multi-column listing of the directories and the names of the files and their extensions in the root directory.

(9) C:\SUE\DOCS> DIR ..\LETTERS

will list the names of the files in the directory LETTERS.

The options /W and /P can be added to any of the above examples.

21.5. Copying Files from One Directory to Another

The COPY command allows files to be copied from one directory to another as well as between disks and within the same directory. When copying from one directory to another the default directory can be any directory.

For example, the file called FILE1.DAT is to be copied from the root directory (the current default directory) into the directory ACCOUNTS and the name is to be changed to FILENEW.DAT.

C:\> COPY FILE1.DAT \ACCOUNTS\FILENEW.DAT

will copy the file. Alternatively

C:\> CD ACCOUNTS

C:\ACCOUNTS> COPY \FILE1.DAT FILENEW.DAT

will do the same copy but this time the default directory is ACCOUNTS. If the filename is to be the same in the new directory then the wildcard character can be used instead of the second filename. For example

C:\ACCOUNTS> COPY \FILE1.DAT *.*

will give the file the same name in the directory ACCOUNTS as it has in the root directory. The *.* can be omitted.

If the default directory is the root directory and a file is to be copied from one directory to another then the full pathname must be given for both the source and target files. For example

C:\> COPY \SUE\LETTERS\FILE1.DAT \ACCOUNTS\NEWFILE.DAT

will copy the file FILE1.DAT from the directory LETTERS to the directory ACCOUNTS and change the name to NEWFILE.DAT.

If the target is an existing directory name, the file can be copied into the directory and given the same name. For example

C:\> COPY \SUE\LETTERS\FILE.DAT \ACCOUNTS

With a hard disk with many sub-directories, changing directories, finding and copy files, et.c. can be time consuming. Fortunately there are many utility programs available, such as XTREE, which simplify file handling.

21.6. The TREE Command

The TREE command displays all of the directories and sub-directories on the default or a specified disk. For example

C:\> TREE

will display on the screen all the directories and the sub-directories on the default disk C.

C:\> TREE A:

will display on the screen all the directories on the disk in drive A.

C:\> TREE A:/F

will additionally give the names of the files in all of the directories on the disk in drive A.

21.7. The PATH Command

On a hard disk, the MS-DOS external commands are usually placed in a sub-directory called, for example, DOS. Unless otherwise instructed the system will only look in the current directory for any commands. The PATH command allows MS-DOS (and other) commands to be available from whichever directory is being used by giving a list of alternative directories which are to be searched.

For example

C:\> PATH C:\;C:\DOS

will set a search path to the root directory and the directory DOS so that external commands stored in either of them will be available from all other directories regardless of the current default directory. This holds true for the current session only.

If the WordPerfect software is placed, for example, in the directory WP51 then in order to access it, as well as the commands in the directory DOS, the PATH command would be

C:\> PATH C:\;C:\DOS;C:\WP51

The semicolon separates the different pathnames which are in the order that they are searched if a command or program is not found in the default directory.

The command PATH by itself will display the path currently set.

As with the prompt command it is useful to include the path command in the AUTOEXEC.BAT file. An example of an AUTOEXEC.BAT file containing this command is given in section 22.2.

22. Batch Files

Batch files are files which contain a series of MS-DOS commands. They are useful in that they can be used to execute a number of commands which are used repeatedly without having to type the commands each time.

All batch files must have a file extension of BAT. When you wish to execute the commands stored in a batch file, type the name of the file (the file extension may be omitted); the commands stored in the file will then be executed sequentially.

22.1. Creating Batch Files

Batch files should be created using a text editor. The standard MS-DOS editor is called EDLIN and will be described in your MS-DOS manual. There are, however, many other, easier to use, editors available; and in fact the latest version of MS-DOS, version 5.0, comes with an editor which is a huge improvement on EDLIN. Note that batch files should generally be text (ASCII) files, i.e. they must not contain the formatting characters that word processors insert. They may also be created using a word processing package such as WordPerfect but must then be saved as ASCII files (using the <Ctrl/F5> function in WordPerfect).

Another method of creating a batch file is by using the MS-DOS COPY command with its first parameter CON (CONsole) followed by the name of a file, i.e. a command of the type

C:/> COPY CON TEST.BAT

This command, means `copy from the console (i.e. the computer's keyboard) to the file TEST.BAT'. Once this command has been given, everything typed on the screen will be copied into the named file until an end-of-file marker is inserted into the file. The end-of-file marker is generated by pressing the <F6> key followed by <Return> or by pressing <Ctrl/Z> followed by <Return>. COPY will then display a message indicating that it has copied the file to disk.

For example

C:\>COPY CON TEST.BAT <Return>

DIR A: <Return>

CHKDSK A: <Ctrl/Z> <Return>

1 File(s) copied

C:\>

If you create a file by this method, you will be unable to make corrections except within the current line (using the <Backspace> key). If the file is saved with errors in it you will have to begin again or edit it.

22.2. The AUTOEXEC.BAT File

The AUTOEXEC.BAT file is a special batch file, which is executed automatically upon start up of the system. To ensure that this occurs, the AUTOEXEC.BAT file must be created within the root directory of the MS-DOS system disk or in the root directory of the hard disk. Execution of the AUTOEXEC.BAT file causes the normal MS-DOS date and time prompts to be bypassed; similarly, the MS-DOS version message is not displayed.

The purpose of the AUTOEXEC.BAT file is to automate a series of commands, for example to tailor the system to your needs as shown in the following examples.

(l) Since the MS-DOS date and time prompts are bypassed when the AUTOEXEC.BAT file is executed, it is a good idea to make the DATE and TIME commands the first two commands of any AUTOEXEC.BAT file, unless your PC has a battery powered clock. The commands DATE and TIME display the prompts to check the date and the time.

ECHO OFF

DATE

TIME

REM This is a remark and has no effect on the

REM execution of the file. It can be used to

REM annotate a batch file

PATH C:\;C:\DOS;C:\WP51;C:\KERMIT;C:\DBASE

KEYB UK

PROMPT $P$G

ECHO OFF stops the commands following it being displayed to the screen as they are executed. The PATH command ensures that you can use any command stored in the root and the directories DOS, WP51, KERMIT and DBASE without that directory having to be the current one. KEYB UK causes the UK keyboard to be loaded and the [[sterling]] sign will then be available on <Shift/3>. The command PROMPT $P$G causes the MS-DOS system prompt to be the current directory's pathname, followed by an angle bracket, as explained earlier.

(2) The following AUTOEXEC.BAT file will load the word processing package WordPerfect immediately upon start up (on a hard disk system). It will also cause the files you have created to be written to and read from the directory WPFILES. As the directory WP51, in which WordPerfect is being stored, is specified on the PATH command the system will automatically search this directory for the file WP.EXE which starts WordPerfect.

DATE

TIME

PROMPT $P$G

ECHO OFF

PATH C:\DOS;C:\WP51

KEYB UK

CD \WPFILES

WP

22.3. Examples of Batch Files

The following batch file is particularly useful for hard disk owners; it is called FORMAT.BAT and prevents accidental formatting of the hard disk when intending to format a blank floppy disk, and consequently erasing all your data from the hard disk. First REN (RENAME) the MS-DOS FORMAT.COM command (on some PCs the FORMAT command has a file extension of EXE).

C:\DOS> REN FORMAT.COM FORM.COM

In this example it has been RENamed to FORM.COM. Be careful not to REName the FORMAT command with the name of an already existing MS-DOS command.

Then create a batch file with the name FORMAT.BAT and store the following line in it,

FORM A:/S

The /S parameter causes the floppy disk being formatted in drive A to be a bootable one; the /S can be omitted if you just wish to use the disk for data files. In order to use the batch file simply type FORMAT and press the <Return> key. You will then be prompted to insert a floppy disk in drive A and press <Return>, at which point the formatting will occur.

23. Further MS-DOS

23.1. The CONFIG.SYS File

The CONFIG.SYS file, as its name implies, configures the system when the PC is booted up. In contrast to the AUTOEXEC.BAT file, which contains commands which can be executed at any time from the DOS prompt, the commands in the CONFIG.SYS file can only be included in the CONFIG.SYS file.

The CONFIG.SYS file is a text file, created by a text editor. The following is a typical example of a CONFIG.SYS.

FILES=20

BUFFERS=30

DEVICE=C:\DOS\MOUSE.SYS

The files command sets the number of open files MS-DOS can access. The buffers command sets the number of disk buffers allocated by MS-DOS on boot-up (a buffer is an area of memory for temporary storage of disk data).

A lot of applications software require you to set the files and buffers to a specified value. So you may have to modify the CONFIG.SYS file before using the application.

The device command installs a device driver on boot-up. In this case the mouse driver is installed.

23.2. The VER Command

The internal MS-DOS command VER, displays the version of MS-DOS being used by your system. It can be useful to know this since some software packages won't run on earlier versions of MS-DOS. This is normally only a problem with old PCs.

24. Application Programs

As well as using a PC to run your own programs you can also run a wide variety of application programs, or packages, on your PC.

Different application packages have different hardware requirements. For example a CAD package may require a 386 PC with a VGA display whereas a word processing package may run adequately on an XT PC. It is important to check that your PC (or a PC you are intending to purchase) is capable of running your desired application package.

Most applications state the hardware configuration required. However it is worth noting that, although a particular package may run on a particular PC system, performance may be very poor.

Hardware considerations include processor type (e.g. 286, 386), video display, co-processor and hard disk size.

The following table gives a list of common applications and popular solutions.

There is a vast amount of public domain and shareware software available for the PC. Public Domain software is made available free of charge. Shareware software is obtainable free of charge but after evaluating the software, and you wish to continue using it, you are `invited' to register your copy, usually at a charge of a few dollars (most shareware originates in the USA).

25. Networking

PCs were designed as single user stand-alone systems. It is possible, however, to link PCs so they are able to share data and peripherals and use electronic mail. PCs are linked via a network. The network is normally controlled from a PC called a fileserver. The fileserver has a large, fast hard-disk containing applications software and data which is available to the other PCs on the network. The advantages of networks are numerous. For example if a new version of a software package were to be used, rather than installing it on every PC in the office, it need only be installed on the fileserver. Also, peripherals such as plotters and printers can be added to the network, allowing sharing of resources.

Creating a network involves additional hardware and software. As well as the cabling involved, each PC in the network needs an expansion card called a network controller. There are several different networking protocols available, the most common being Ethernet. Software is also needed to control the network, the standard for PC networks being Novell Netware.

Glossary of Terms

Address: the number allocated to a memory location allowing the PC to access the data in that location.

ANSI: American National Standards Institute.

Application: software designed for a specific purpose. e.g. word processing, spreadsheet.

ASCII: American Standard Code for Information Interchange. A standard code for relating characters to numbers. e.g. the ASCII code for `A' is 65.

AT: Advanced Technology. The replacement for the XT PC. Still the standard for most PCs.

Baud: rate of data transfer (one bit per second). Used in communications e.g. modems.

BIOS: Basic Input Output System. Software stored in ROM which controls the basic functions of the PC.

Bit: Binary digIT. Basic unit for data.

Bitmap: a graphics image which is made up of dots, each dot taking up one bit of data.

Buffer: a temporary store for data being transferred. e.g. from and to disks.

Bus: electronic tracks which carry data between different parts of the PC. Equivalent to motorway.

Byte: 8 bits of data. Usually enough to store 1 character.

Cache: an area of memory used for fast data transfer.

CAD: Computer Aided Design/Drafting.

CD-ROM: Compact Disk-Read Only Memory. CDs are capable of holding vast amounts of data. Currently PCs cannot write data to CDs.

Centronics: another name for the parallel port.

CGA: Color Graphics Adapter. A graphics display standard.

Clone: A PC which is compatible (i.e. will run the same software) as an IBM PC.

CPU: Central Processing Unit. An IC which is the `brain' of a PC.

DDE: Dynamic Data Exchange. A function of Windows 3 that allows the flow of data between application programs.

Device driver: a program which needs to be in memory to allow the PC to drive a particular peripheral.

Diablo: standard for daisywheel printers.

Dot Matrix: impact printer.

DPI: Dots Per Inch. Method of quantifying laser printing quality.

DRAM: Dynamic Random Access Memory.

DTP: Desk Top Publishing. An application package which allows the mixing of text and graphics to produce documents/newsletters etc.

EGA: Enhanced Graphics Adapter. A graphics display standard.

EISA: Extended Industry Standard Architecture. Designed as the successor to AT (or ISA).

EPROM: Erasable Programmable Read Only Memory.

EPSON: Printer manufacturer.

Ethernet: A protocol and cabling system for operating local area networks.

Expanded Memory: paged memory.

Expansion Card: printed circuit board slotted into an expansion slot inside the PC.

Extended Memory: memory available to AT type machines at addresses above 1 Mb.

FAT: File Allocation Table. Part of a disk which holds information on where all the files on that disk are located.

File: a block of information stored on disk.

Fileserver: a PC used in a network.

Font: a particular size and style of a typeface. e.g. 12 point Times Italic. Times is the typeface, 12 point is the size, italic is the style.

Footprint: The amount of space the PC takes up on the desktop.

GEM: Graphics Environment Manager. see GUI.

GUI: Graphical User Interface. System where the DOS command line is replaced by a mouse controlled environment consisting of icons, windows and menus. Also known as a WIMP system. Examples include GEM and Windows 3.

Hercules: A monochrome graphics display standard.

HPGL: Hewlett Packard Graphics Language. Language used to describe output for plotters.

IC: Integrated Circuit or `chip'.

Icon: graphical representation of a file or a running application. see GUI

ISA: Industry Standard Architecture. Another name for the AT type PC.

Ink-jet: type of printer.

Integrated Package: a software package that combines word processing, database, spreadsheet etc. functions in one program.

Intel: CPU manufacturer.

Interface: Software or hardware that allows communication between two pieces of software or hardware.

Interleave: refers to the way data is stored on hard disks.

Kermit: software that facilitates file transfer between computers.

Kilobyte (Kb): 1,024 bytes.

LAN: Local Area Network.

Language: a way of writing programs.

Laptop: a portable PC.

MCA: Micro Channel Architecture.

MDA: Monochrome Display Adapter. The original display standard for PCs. Could display text only; no graphics capability.

Megabyte (Mb): 1,024Kb or 1,048,576 bytes of data.

Memory: electronic circuitry for storing data and programs.

Modem: MOdulator/DEModulator. Device that allows the PC to communicate with other computers via the telephone system.

Motherboard: a printed circuit board inside the PC which holds all the principal ICs and circuitry.

MS-DOS: MicroSoft Disk Operating System. Operating system used by PCs.

Multisynch: A monitor which is capable of running at several different speeds. Thus capable of accepting signals from different graphics adapters.

Multitasking: the process of running more than one program simultaneously. Not normally seen on PCs.

Network: a group of interconnected computers.

Notebook: A small (usually A4) portable PC.

OCR: Optical Character Reader. Software used in conjunction with a scanner to `read' printed text into a PC.

Operating System: computer program which provides the link between the user, the hardware and software. e.g. MS- DOS, UNIX.

Optical Disk: a storage device capable of storing more data than hard disks see CD-ROM.

OS/2: Operating System 2. Designed by IBM as a successor to PC-DOS.

Parallel: transmitting data down more than one line (as opposed to serial, where one line only is used).

Path: the route MS-DOS takes to find a file.

PC-DOS: Personal Computer Disk Operating System. Equivalent to MS-DOS.

Pixel: a dot on the screen. The screen image consists of an array of pixels.

Port: A socket in the PC allowing devices, such as printers, to be connected.

Portable: A battery powered PC.

Postscript: A page description language used by laser printers.

PPM: Pages Per Minute. Method for measuring laser printer speeds.

Presentation Manager: A GUI designed for use under OS/2.

Program: A set of instructions which the CPU carries out.

PROM: Programmable Read Only Memory.

Protocol: a mutually agreed way of doing things between a computer and another computer or peripheral.

PS/2: Personal System 2. A computer designed by IBM as a successor to the AT.

RAM: Random Access Memory. The working area memory. Its contents are lost when the PC is switched off.

RAM Disk: an area of memory configured to behave like a disk drive.

ROM: Read Only Memory. Memory that can be read from but not written to. i.e. its contents stays the same.

RS232: see serial port.

Scanner: device which can `scan' an image (e.g. photo or printed page) into a PC.

SCSI: Small Computer Systems Interface.

Serial port: socket in the back of the PC for sending and receiving information. Used for mouse and/or communications.

SIMM: Single In-line Memory Module. A memory chip.

Software: programs and data.

Spreadsheet: an application program that displays rows and columns allowing data contained within to be analyzed. Useful for financial calculations and planning.

SQL: Structured Query Language. Language used for querying databases.

Super-VGA: a non-standard extension of VGA with higher resolution and more colours.

System disk: the disk (hard or floppy) a PC needs to start up (or boot-up) from.

Tape streamer: a disk back-up system.

Terminal Emulator: software which makes a PC behave like a mainframe terminal.

Toner: black powder used by laser printers.

Tower system: a floor standing PC.

TPI: Tracks Per Inch. Refers to the density of floppy disks.

TSR: Terminate and Stay Resident. A program which still resides in memory when not in use and is usually called up by a simple key combination.

Typeface: the design for a set of characters. e.g. Helvetica, Courier. See font.

UNIX: an operating system sometimes found on PCs.

VGA: Video Graphics Array. Display standard allowing high resolution graphics to be produced.

Virtual Memory: technique where hard disk space is made to appear like extra system memory. Used by Windows 3.

WIMP: Windows Icon Menus and Pointer. See GUI.

Winchester: another name for a hard disk.

Windows: see GUI

WORM: Write Once Read Many. Refers to optical (CD) disks.

WYSIWYG: What You See Is What You Get. Applies to word processors. What you see on the screen is how the document will appear when printed.

XT: eXtended Technology. The successor to the original PC.











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