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Hard Drive: WESTERN DIGITAL: AC-1170 171MB 3.5"/SL IDE / AT




A C - 1 1 7 0    WESTERN DIGITAL
NO MORE PRODUCED                                      Native|  Translation
                                                      ------+-----+-----+-----
Form                 3.5"/SLIMLINE         Cylinders    2233| 1010|     |
Capacity form/unform   171/      MB        Heads           2|    6|     |
Seek time   / track  13.0/ 4.0 ms          Sector/track     |   55|     |
Controller           IDE / AT              Precompensation
Cache/Buffer            32 KB              Landing Zone
Data transfer rate    1.250 MB/S int       Bytes/Sector      512
                      5.750 MB/S ext
Recording method     RLL 1/7                        operating  | non-operating
                                                  -------------+--------------
Supply voltage     5/12 V       Temperature *C         5 55    |    -40 60
Power: sleep          0.3 W     Humidity     %         8 80    |      5 95
       standby        0.3 W     Altitude    km    -0.305  3.048| -0.308 12.200
       idle           1.5 W     Shock        g        10       |     70
       seek               W     Rotation   RPM      3322
       read/write     3.0 W     Acoustic   dBA        36
       spin-up       12.0 W     ECC        Bit   176,REED SOLOMON
                                MTBF         h     250000
                                Warranty Month        24
Lift/Lock/Park     YES          Certificates     CSA,SDA,FCC,IEC950,TUV,UL1950

Layout

WESTERN CAVIAR AC1170/AC2250/AC2340 TECHNICAL REFERENCE MANUAL

  +---------------------------------------------------------+
  |                                                         |XX
  |                                                         |XX J2
  |                                                         |XX Inter-
  |                                                         |XX face
  |                                                         |XX
  |                                                         |.X
  |                                                         |XX
  |                                                         |XX
  |                                                         |XX
  |                                                         |XX
  |                                                         |X1
  |                                                         |+-+
  |                                                         || |J8
  |                                                         |+-1
  |                                                         |XX Power
  |                                                         |XX J3
  +---------------------------------------------------------+  1

Jumpers

WESTERN CAVIAR AC1170/AC2250/AC2340 TECHNICAL REFERENCE MANUAL

Jumper setting
==============

J8 Master/Slave/Cable Select Configuration
-------------------------------------------

    +5-3-1+ Single Drive              +5-3-1+ Master Drive
    |o o o| Configuration             |X o o| Configuration
    |o o o|                           |X o o| (Dual Drives)
    +6-4-2+                           +6-4-2+

    +5-3-1+ Slave Drive               +5-3-1+ Cable Select
    |o X o| Configuration             |o o X| Configuration
    |o X o| (Dual Drives)             |o o X| (Dual Drives)
    +6-4-2+                           +6-4-2+

The Caviar can be assigned as either a single, master, or slave
drive.

Single Drive Mode
-----------------
If you are installing the Caviar drive as the only intelligent drive
in the system, you do not need install jumpers on the J8 connector.
This is considered a standard single drive installation, and no
jumpers are required. Note that even with no jumper installed, the
Caviar checks the DRIVE ACTIVE/SLAVE PRESENT (DASP) signal to de-
termine if a slave intelligent drive is present.

If you have a dual installation (two intelligent drives), you must
designate one of the drives as the master and the other as the slave
drive. The jumper pins on the J8 connector need to be configured for
the dual installation.

Master Drive Mode
-----------------
To designate the drive as the master, place a jumper shunt on pins
5-6. With the Caviar configured as the master drive, the Caviar
assumes that a slave drive is present. The jumper on pins 5-6 is
optional if the slave drive follows the same protocol (Common Access
Method AT Bus Attachment) as the Caviar.

Slave Drive Mode
----------------
To designate the drive as the slave, place a jumper shunt on pins
3-4. When the Caviar is configured as the slave drive, the Caviar
delays spin up for three seconds after powerup reset. This feature
prevents overloading of the power supply during powerup.

Cable Select (CSEL)
-------------------
Caviar also supports the CSEL signal on the drive cable as a drive
address selection. Place a jumper shunt on pins 1-2 to enable this
option. When enabled, the drive address is 0 (Master) if CSEL is low
or 1 (Slave) if CSEL is high.

 J3   DC Power and pin connector assignments
 -------------------------------------------
      +------------+   pin 1    +12 V
      | 4  3  2  1 |   pin 2    GND
      +------------+   pin 3    GND
                       pin 4    + 5 V

Install

WESTERN CAVIAR AC1170/AC2250/AC2340 TECHNICAL REFERENCE MANUAL

Notes of Installation
=====================

Installation direction
----------------------

     horizontally                           vertically
   +-----------------+             +--+                       +--+
   |                 |             |  +-----+           +-----+  |
   |                 |             |  |     |           |     |  |
 +-+-----------------+-+           |  |     |           |     |  |
 +---------------------+           |  |     |           |     |  |
                                   |  |     |           |     |  |
                                   |  |     |           |     |  |
 +---------------------+           |  +-----+           +-----+  |
 +-+-----------------+-+           +--+                       +--+
   |                 |
   |                 |
   +-----------------+

Orientation
-----------
The Caviar can be mounted in many different ways depending upon the
physical design of your system.

Determining Your Configuration
------------------------------
You can configure the Caviar in one of two ways:

 1. The drive is cabled directly to a 40-pin connector on the mother-
    board, or
 2. The drive is cabled to an adapter card mounted in one of the
    expansion slots in the computer.

Both configurations use a 40-pin host interface cable.

If you are using the Caiar drive as one of two hard disk drives in
the computer (dual installation), you may use either configuration.
In dual installations, you must use a 40-pin host interface cable
with three connectors and daisy-chain the two drives to the mother-
board or adapter card.

Dual Installations
------------------
Dual Installations require a master/slave drive configuration, where
one drive is designated as the promary (master) drive and the other
is designated as the secondary (slave) drive. The Caviar drive is
compatible in dual installations with other intelligent drives that
support a master/slave configuration.

If your installation requires the use of an adapter card, it is
useful to know that you may also be able to connect your floppy
drive(s) to the adapter card.

Mounting the Drive
------------------
For dual installations, it is usually easier to completely install
one intelligent drive in the lower position first. The order of
intelligent drives is unimportant if you are using to Western Digital
drives. As explained previously, one must be jumpered as the master
drive and the other as the slave drive. When installation is complete
the drives are daisy-chained together.

Cabling and Installation Steps
------------------------------
Make sure your interface cable is no longer than 18 inches to
minimize the noise which is induced on the data and control buses.
Also, if you are connecting two drives together, you need a daisy-
chain cable that has three 40-pin connectors.

Caution: You may damage the Caviar drive if the interface cable is
not connected properly. To prevent incorrect connection, use a cable
that has keyed connectors at both the drive and host ends. Pin 20
has been removed from J2 connector. The female connector on the
interface cable should have a plug position 20 to prevent incorrect
connection. Make sure that pin 1 on the cable is connected to pin 1
on the connectors.

Mounting Screws
---------------
Mount the caviar drive bay using four 6-32 screws. Be sure to use the
correct size screws. Do not install the screws past six threads
(3/16 inch). Screws that are too long will damage the Caviar drive.

Power Connectors and Cables
---------------------------
Power Connector: 4-pin MOLEX P/N 15-24-4041 or equivalent

 Mating Connector:          Body AMP 1-480424-0 or equivalent
                            Pins AMP 60619-4 or equivalent

Power Cable Wire Gauge 18 AWG

Buffer RAM
----------
A 32/64-Kbyte (optional 128/256-Kbyte) static RAM buffer enhances
data throughput by buffering sector data between the Caviar and the
AT system bus. The buffer is accessed by two channels, each having a
separate 16-bit address and byte-count register. The channels operate
simultaneously, accepting read and write operations from two data
paths.

Spindle Motor
-------------
The spindle motor assembly consists of a brushless three-phase motor,
spindle bearing assembly, disk mounting hub and a ferrofluid magnetic
seal. The entire spindle motor assembly is completely enclosed in the
HDA and bolted to the base casting. The motor rotates the spindle
shaft at approximately 3322 RPM.

Proprietary spindle electronics sense motor speed and angular
position by monitoring the spindle motor's back electromotive force
(BEMF). Using BEMF sensing, instead of the Conventional Hall effect
ot inductive motor position sensors, lowers the power consumption and
increases reliability. Motor driver circuits ynamically brake the
spindle during motor spin down.

Translation
-----------
The Caviar implements linear address translation. The translation
mode and translated drive configuration are selected by using the Set
Drive Parameters command to issue head and sector/track counts to the
translator. Caviar supports universal translation, therefore, any
valid combination of cylinder, head and SPT can be assigned to the
drive, as long as the total number of sectors is not greater than the
physical limits. The product of the cylinder, head and sectors/track
counts must be equal to or less than the maximum number of sectors
available to the user. The maximum number of sectors per drive are:

AC1170 - 333,300
AC2250 - 499,950
AC2340 - 666,600

Each sector consists of 512 bytes.

The minimum values for any translation parameter is one. The maximum
value for any translation parameter is as follows:

Sectors/Track - 255
Heads - 16
Cylinders/Drive - 2048

Features

WESTERN CAVIAR AC1170/AC2250/AC2340 TECHNICAL REFERENCE MANUAL

Zoned Recording
---------------
The AC1170, AC2250, and AC2340 drives employ Zoned Recording to in-
crease the data density on the outer tracks of the drive. The outer-
most tracks contain 71% more sectors than the innermost tracks,
thereby increasing the total capacity of the drive.

Advanced Defect Management
--------------------------
The Caviar is preformatted (low-level) at the factory and comes with
a full complement of defect management functions. Extensively tested
during the manufacturing process, media defects found during
intelligent burn in are mapped out with Western Digital's high
performance defect management technique. No modifications are
required before installation.

Embedded Servo Control
----------------------
The Caviar festures an embedded servo concept as the means of
providing sampled position feedback information to the head position
servo system. This high sampling rate supports the high frequency
servo bandwidth required for fast access times as well as highly
accurate head positioning. The embedded servo concept provides the
means of generating accurate feedback information without requiring
a full data surface as would a dedicated servo control concept.

Servo bursts are located along a radial path from the disk center,
ensuring that head positioning data occurs at constant intervals.

Seek Time
---------
Average Seek Sub-13 Milliseconds
Track-to-Track Seek 4 Milliseconds
Maximum Seek 26 Milliseconds
Index Pulse Period 18 Milliseconds
Average Latency 9 Milliseconds

Voice Coil Assembly
-------------------
The voice coil assembly consists of an upper and lower magnetic plate
a flat rotary coil, a bidirectional crash stop and a pivot bearing.
The pivot assembly fits in the actuator block bore.

Defect Management
-----------------
Every Caviar undergoes factory-level intelligent burn in, which
thoroughly tests for and maps out defective sectors on the media
before the drive leaves the manufacturing facility. Following the
factory tests, a primary defect list is created. The list contains
the sector cylinder and head numbers for all defects. The purpose of
the sector/track map is to manage the reallocation of spare sectors
and tracks after they have been assigned.

Defects managed at the factory are sector slipped. Grown defects that
can occur in the field are handled by realocation to spare sectors on
the inner cylinders of the drive.

Format Characteristics
----------------------
In order to be compatible with existing industry standard defect
management utility programs, the Caviar supports logical format. When
the host issues the Format Track command, the Caviar performs a
logical version of this command in response to the host's interleave
table request for good and bad sector marking or assign/unassign the
sector to/from an alternate sector.

If the host issues the Format Track Command during normal operating
modes, the data fields of the specified track are filled with a data
pattern of all zeros. The interleave table identifies any bad sectors
on a given track. The interleave table must contain all appropriate
number of bytes of data. There are two bytes per sector for each
entry in the interleave table. The first byte marks the sector as
good or bad.

General

WESTERN TIPS

 WESTERN DIGITAL 3.5-INCH DRIVES FREQUENTLY ASKED QUESTIONS
 ----------------------------------------------------------
 1) Will a Caviar drive work in my system?
   If your computer is 100% AT compatible and has either a 40-pin AT
   IDE interface on the motherboard or an IDE controller card with a
   40-pin data cable.

 2) What are the master/slave jumper settings on Western Digital
    drives?
    All Western Digital drives are configured the same. On the back of
    the drive between the 4-pin power connector and the 40-pin data
    connector, there is a jumper block J8 consisting of 6 pins.
    Western Digital hard drives are shipped with a jumper shunt in the
    neutral storage position (across pins 5 and 3) for future dual
    drive use.

 - If you are installing the Western Digital hard drive as the only
   hard drive in your system, leave the jmper shunt in the neutral
   storage posiition. Jumper shunts are not required for single hard
   drive installations.

 - To designate the Western Digital hard drive as the master (C:),
   place a jumper shunt on pins 5-6

 - To designate the Western Digital hard drive as the slave (D:),
   place a jumper shunt on pins 3-4.

 3) What are the drive type and the drive parameters in the CMOS, for
    Western Digital drives?
    On top of the drive, the number of cylinders, heads and sectors
    per track are printed on the label. Precomp and L-zone should be
    set equal to the drive's cylinder count + 1. Select user type or
    custom type (typically type 41 or 42) for your drive. This will
    allow you to type in the parameters. Older systems that do not
    offer a user type can either upgrade the system BIOS or set the
    drive to drive type 1 (which should be a smaller drive size), and
    run Ontrack Disk Manager from A drive to get the full capacity of
    the drive. If you do not follow one of these procedures and your
    system is pre-1994, you will be limited to the largest size drive
    your BIOS will allow.

 4) What is the Ontrack Disk Manager software that came with my drive
    and what does it do?
    Ontrack Disk Manager is the original hard disk installation
    package that will initialize, partition, and prepare your hard
    drive for use. Ontrack Disk Manager also allows you to access the
    full capacity of the drive even when your system BIOS can't. It is
    compatible with 32-bit disk access.

Note: Ontrack Disk Manager must be installed from floppy drive A. If
your A drive is a 5.25-inch floppy drive, copy the contents of your
Ontrack Disk Manager disk to a formatted 5.25-inch disk and re-run
Ontrack Disk Manager.

 5) I just installed Ontrack Disk Manager on my Caviar drive and tried
    to install DOS. DOS attempted to write to my drive and it
    formatted my drive back to 528 MB which is my BIOS limitation. How
    do I install DOS and still get the full capacity of my drive?
    After Ontrack Disk Manager installation, you must create an
    Ontrack Disk Manager rescue disk. There are two ways of
    accomplishing this:

OPTION 1:
- Create a clean DOS bootable disk.

 - Copy 2 files from the Ontrack Disk Manager disk to your bootable
   disk: XBIOS.OVL, and DMDRVR.BINs Create a CONFIG.SYS file on this
   bootable disk with these 3 lines: DEVICE=DMDRVR.BIN FILES=35
   BUFFERS=35

- Remove the floppy and reboot the system.

 - When you see the message "Press spacebar to boot from diskette",
   press the spacebar (system halts).

- Insert the rescue disk in the A: drive.

- Press any key (system resumes boot process).

 - At the A: prompt, remove rescue disk, insert DOS installation disk
   and type SETUP.

 - You can now install DOS without overwriting the Ontrack Disk
   Manager files.

OPTION 2:

- Create a clean DOS bootable disk.

- Insert Ontrack Disk Manager disk in the A: drive.

 - At the A prompt, type: DMCFIG/D=A:. You will be prompted to insert
   a bootable floppy in the A: drive.

 - Follow the prompts on the screen. Ontrack Disk Manager will ask you
   to change disks a few times.

- Continue until Ontrack Disk Manager is finished.

- Remove the floppy and reboot the system.

 - When you see the message "Press spacebar to boot from diskette".
   Press the spacebar (system halts).

- Insert the rescue disk in A drive.

- Press any key (system resumes boot process).

 - At A prompt, remove rescue disk, insert DOS installation disk and
   type SETUP.

 - You can now install DOS without overwriting the Ontrack Disk
   Manager files.

 6) CHKDSK or SCANDISK reports a few bad sectors. How do I go about
    fixing the problem.
    You can use the Western Digital defect management utility WDATIDE.
    One of its options is the comprehensive surface analysis. This
    procedure will mark all grown defects bad if indeed there are any
    and it will compensate for the lost capacity by utilizing spare
    tracks.

Note: This utility is data destructive. Back up all data on the drive
before using it. Due to the thoroughness of this operation, WDATIDE
can take quite a bit a time depending on the capacity of your drive.

 7) Do I have to do anything with my original drive when adding a new
    drive to my system?
    Yes, one hard drive must be designated as the master drive
    (preferably the newer, faster drive) and the other must be
    designated as the slave drive. Typically, most drives need to have
    a jumper placed on them to specify the Master or Slave position.
    For information on non-Caviar hard drives, please contact the
    appropriate manufacturer.

 8) I installed my new drive and entered the drive parameters in the
    CMOS, but the drive will not boot or it displays the message "HDD
    controller failure."
    Your drive must be partitioned and formatted before it will be
    bootable. If your system will support drives larger than 528 MB,
    and you have a copy of MS-DOS or PC-DOS version 5.0 or greater,
    insert the setup diskette in your floppy drive and turn on your
    computer. Follow the prompts and DOS will partition and format the
    drive for you.

If you do not have a copy of MS-DOS or PC-DOS version 5.0 or greater,
you will need to boot from a bootable disk and then run the FDISK
command to partition your drive, and then format the drive using the
DOS FORMAT command. After running format, you should be able to
reboot your computer from your hard drive.

 9) How can I use the full capacity of my Caviar drive of 540 MB or
    greater?
    You can use Ontrack Disk Manager to obtain full capacity if your
    system does not support LBA mode. If your system does support LBA
    mode, you can enable LBA in your CMOS setup utility.

 10) How can I get 32-Bit Disk Access in Windows on my Caviar AC2540,
     AC2700 or AC31000 in Windows 3.1x? If your BIOS supports the
     drive at full capacity (i.e., the BIOS supports Logical Block
     Addressing) you use WDCDRV.386, Western Digital's FastDisk device
     driver. This driver is contained in a file named WIN31.EXE
     available for downloading from our bulletin board (714/753-1234),
     our Web server (WWW.WDC.COM), our FTP site (FTP.WDC.COM), our
     forum on the Microsoft Network (Go word WDC), and our forum on
     America On-line (keyword WDC). If your BIOS does not support LBA
     mode and you have installed your drive using Ontrack Disk Manager
     (v6.03 and above), run DMCFIG to install WDCDRV.386 and obtain
     32-Bit Disk Access.

 11) My drive will not spin up or spins down after a few seconds.
     This is a drive failure. Return the drive to the distributor or
     contact a technical support representative to receive a Return
     Materials Authorization (RMA).

 12) CMOS, FDISK and File Manager in Windows report less than the
     capacity of my new drive, but CHKDSK reports the right number of
     bytes. Which is correct?
     Setup (CMOS) and FDISK use a binary definition of a megabyte
     which is calculated at 1,048,256 bytes per megabyte. All hard
     drive manufacturers and the DOS CHKDSK utility use a decimal
     definition of a megabyte which is calculated at 1,000,000 bytes
     per megabyte. This is why some utilities show 515 MB for a 540
     megabyte drive and some show the actual number.

 13) How Can I install OS/2 for Windows, OS/2 3.0 WARP, Windows NT
     3.5x or Windows 95 on my drive which was initially installed
     using Ontrack Disk Manager?
     If you have Ontrack Disk Manager version 6.03, 6.03a, or 6.03b,
     download the file named DMPATCH.EXE from Western Digital's online
     services: ftp site: ftp.wdc.com

World Wide Web Site: http://www.wdc.com/
Microsoft Network (MSN) - Go word WDC
America Online (AOL) - Keyword: Western Digital
Western Digital's BBS at (714) 753-1234
This file has the latest Ontrack Disk Manager drivers which will
allow you to install OS/2 version 2.1x, OS/2 WARP, Windows NT 3.5x
or Windows 95 on your hard drive. Please read the included readme
file with this file for further detail.

14) My drive will work as a slave but not as a master (or vice-
versa).
Check master/slave jumpers on all drives. Also, some drive's speed
and timing differ drastically as to the initial spinup sequence. This
might confuse the system and cause one of the drives not to be
recognized. The best solution for this situation is to exchange
drives (make the master a slave and vice-versa).

 15) My drive will not partition when I run FDISK. It hangs the system
     or it displays the message: "Runtime error."
     This is usually caused by corruption or damage to track zero. Use
     the Western Digital utility WDFMT to format the drive. If that
     does not help, call Western Digital Technical support at
     1-800-ASK-4-WDC to get further instructions.

 16) Can a hard drive be mounted on it's side, edge, or upside down?
     Drives can be mounted on any side but it is preferable to mount
     the drive right side up. It is also important to use all four
     screws to hold the drive firmly in place.

Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T.)
----------------------------------------------------------------
S.M.A.R.T. enables a drive's internal status to be monitored through
diagnostic commands at the host level.

The Caviar AC21600, AC32100 and AC32500 drives monitor read error
rate, start/stop count, spin-up retry count, and drive calibration
retry count. All of these attributes are updated and stored on the
hard drive in the reserved area of the disk. The hard drive also
stores a set of attribute thresholds that correspond to the
calculated attribute values. Each attribute threshold indicates the
point at which its corresponding attribute value achieves a negative
reliability status.
====================================================================

QUESTION
Which hard drive specification is most important to overall
system performance ?

- Host Transfer Rate
- Drive RPM (revolutions per minute)
- Disk Transfer Rate (Media Rate)
- Seek Time
- Cache Size
- PC Data Handling
- All of the above

Answer
The correct answer is actually a combination of "all of the above,"
keeping in mind most of the above specifications are interrelated
when it comes to optimizing system performance.

The pie chart illustrates the relative influence of factors affecting

drive performance during a typical random I/O operation (reading
and writing to a hard drive).

The major determinate of hard drive performance is mechanical
factors which are one hundred times slower than the high-speed
electronics contained in a drive.

Factors Affecting Hard Drive Performance
(In their relative order of importance)

MECHANICAL LATENCIES
Mechanical Latencies include both Seek Time and Rotational
Latency. The seek time is a measure (in milliseconds) of how
fast the hard drive can move its read/write heads to a desired
location. Rotational latency is a measure of the average time
(also in milliseconds) the read/write heads must wait for the
target sector on the disk to pass under them once the read/write
heads are moved to the desired target track.

Mechanical latencies are the main hindrance to higher performance
in modern Enhanced IDE (EIDE) hard drives. The time delays of
mechanical latencies are one hundred times higher than
electronic (non-mechanical) latencies associated with the
transferring of data. Therefore, reducing mechanical latencies
(a lowering of seek time and rotational latency) should be the
top consideration in improving hard drive performance.

RPM
This is the rotational speed of the media (disk), also referred
to as the spindle speed. Hard drives only spin at one constant
speed. Typical speeds are 3600 to 3880, 4500, and 5200 to 5400
revolutions per minute. The slower the RPM, the higher the
Mechanical Latencies. Disk RPM is a critical component of hard
drive performance because it directly impacts the rotational latency
and the Disk Transfer Rate explained below.

DISK TRANSFER RATE
The Disk Transfer Rate (sometimes called media rate) is the
speed at which data is transferred to and from the disk media
(actual disk platter) and is a function of the recording frequency.
Typical units are bits per second (BPS), or bytes per second.
Modern hard disks have an increasing range of Disk Transfer
Rates from the inner diameter to the outer diameter of the disk.
This is called a "zoned" recording technique.

The key media recording parameters relating to density per platter
are Tracks Per Inch (TPI) and Bits Per Inch (BPI). A track is a
circular ring around the disk. TPI is the number of these tracks
that can fit in a given area (inch). BPI defines how many bits
can be written onto one inch of a track on a disk surface. To
greatly simplify, the Disk Transfer Rate (the rate at which data
is read and written to the disk) is dependent upon the speed of
the disk (RPM) and the density of the data on the disk (BPI).
Even most modern, high-speed, 5000 RPM hard drives are generally
limited to a maximum Disk Transfer Rate of approximately 9 to 10
MB per second. This specification is critical to performance and
must be weighed carefully against such electronic latencies as
Mode 3 PIO and Mode 4 PIO host transfer rates explained below.

PC DATA HANDLING
After the data moves down the IDE cable from the drive to the host
interface, there are several factors that can affect drive
performance over which the hard drive has no control. PC Data
Handling is independent from the hard drive and very dependent
upon the CPU type and speed, the BIOS overhead (how the system
issues commands to the hard drive), speed and size of the system
RAM and RAM cache, CPU-to-memory speed, and storage subsystem
performance. PC Data Handling is also affected by the caching
methods of such software applications as SMARTDRIVE, 32-bit
disk access operating system drivers, etc.

HOST TRANSFER RATE
The speed at which the host computer can transfer data across the
IDE or EIDE interface. Processor Input/Output (PIO) modes and
Direct Memory Access (DMA) modes are defined in the ATA-2 industry
specification as follows:

Mode 3 PIO 11.1 MB/sec
Mode 4 PIO 16.6 MB/sec
Mode 1 DMA 13.3 MB/sec
Mode 2 DMA 16.6 MB/sec

Modern host computer systems usually support most of the above
modes. Faster Host Transfer Rates in the future will use multi-word
DMA modes as the industry will not support any future PIO mode
standards beyond mode 4.

The computer system manufacturer is responsible for implementing a
Host Transfer Rate that is high enough to ensure that the host
computer is not the performance bottleneck. Implementing
increasingly higher Host Transfer Rates without corresponding
increases in Disk Transfer Rates on the hard drive will not result
in increased drive performance.

Cache Buffer Size - Is Bigger Always Better ?
A Cache Buffer is similar to a water glass. When you are writing
to a hard drive, the host computer fills the glass and the disk
media empties it. If you are reading data from a hard drive, the
disk media fills the glass and the host computer empties it.

The reason that a bigger cache buffer is not always better
(or faster) is because the host computer (with Mode 4 PIO or
Mode 2 DMA capabilities) can empty or fill the glass much faster
than the hard drive can empty or fill it. When the host system can
transfer data in or out of the cache buffer faster than the media
rate, a larger buffer size becomes irrelevant because the host
system is always "waiting" for the hard drive.

Western Digital hard drives are designed with cache buffer sizes
that are matched to the Disk Transfer Rate capabilities of the
drive and the Host Transfer Rates of modern computer systems. All
of our drives are benchmarked with various cache buffer sizes to
verify that the most cost-effective and performance-effective
cache size is implemented.

Confusion Over Mode 4 and Mode 2 DMA
The Enhanced IDE program created the long-range road map for
performance enhancements which included faster disk and host
transfers, Mode 3, Mode 4, Mode 2 DMA, etc. Currently, computer
systems and hard drive controller silicon have most of the elements
needed to implement Mode 4 PIO or Mode 2 DMA (a 16.6 MB/sec Host
Transfer Rate). However, to take advantage of these performance
modes, physical drive architecture must also make some performance
improvements in the area of Mechanical Latencies and Disk Transfer
Rate (media rate) as defined earlier.

Some competitors, in their eagerness to supply a new feature, are
prematurely marketing Mode 4 and Mode 2 DMA. While their drive
controller silicon supports these modes (which is very easy and
inexpensive to implement), spindle speeds (RPM), rotational latency,
bit density, and other factors have not yet been improved (these
being very difficult and costly). The result is hard drives which
have the electronic capability to do Mode 4 and Mode 2 DMA transfer
rates, but can't take advantage of these modes due to the slower
Disk Transfer Rate of the drive.

Western Digital will not be implementing Mode 4 or Mode 2 DMA on
older drive products as the host systems into which these drives
are designed are not electrically capable of these data transfers,
nor are the Disk Transfer Rates on these drives beyond current Mode
3 capabilities. As next generation systems are introduced, they will
be paired with next generation drives. Those drives will require
and offer true Mode 4 / Mode 2 DMA capability from a total drive
architecture standpoint.
=====================================================================
AC2540/2635/2700/2850/21000/31000/31200/31600

Windows 95 Operating System Addendum
------------------------------------
The information in this addendum supersedes that supplied in Windows
95 section on pages 35 and 36 of this manual. Please refer to thos
addendum for Windows 95 questions.

Although Windows 95 is capable of recognizing the full capacity of
hard drives larger than 528 MB in systems with a translating BIOS,
some restrictions apply to systems without a translating BIOS.

For Systems With a Translating BIOS
-----------------------------------
Enter your CMOS setup and select a drive type that will recognize the
full capacity of your drive. This is usually done by selecting the
auto config drive tape. The boot partition can be set up to be as
large as the full capacity of your hard drive.

For Systems Without a Translating BIOS
--------------------------------------
Enter your CMOS setup and select a user defined drive type. Enter
these parameters: cylinders = 1024, heads = 16, sectors = 63. Your
system's total disk space will be limited to a maximum of 528MB.

If you want your system to utilize more than 528 MB of disk space,
you must use Ontrack's Disk Manager software (or a similar third-
party installation software).

Installing Windows 95 on a Hard Drive with Ontrack Disk Manager
Already Installed
---------------------------------------------------------------
The Windows 95 installation program will analyze your computer
system and install seamlessly with Ontrack Disk Manager.

Computer Systems with Windows 95 Already Installed
--------------------------------------------------
If you are installing a Western Digital hard drive and Ontrack Disk
Manager on a computer system with Windows 95 already installed, you
must install Ontrack Disk Manager as described here.

 Enter your CMOS setup and select a user defined drive type. Enter
 these parameters for drives with capacities over 528MB:
         Cylinders = 1024, Heads = 16, Sectors = 63.

Save these changes and reboot your computer.

 1. Select the Start icon from the Windows 95 main screen.
    DO NOT open an MS-DOS menu from Win 95 to install Ontrack Disk
    Manager.

2. Choose the Shut Down option.

 3. Select Resatrt Computer in DOS mode. When your computer restarts,
    you should be at the DOS prompt.

4. Install Ontrack Disk Manager.

Windows 95 will noe recognize the full capacity of your hard drive
and run in 32-bit disk access mode for optimum performance.













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