64 What are VGA/SVGA/UVGA/8514/a/XGA?
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
64 What are VGA/SVGA/UVGA/8514/a/XGA?
The wonderful thing about PC's is that there are standards for so many different things. The problem is that every company has their own standards ;-). The lack of a widely accepted standard for >VGA pixel addressabilities is causing plenty of problems for manufacturers, system builders, programmers and end users. As a result, each vendor must provide specific drivers for each supported operating system for each of their cards. In the list above, VGA, 8514/a and XGA are standards established by IBM, and have been accepted to a greater (VGA), lesser (XGA) or even much less (8514/a) degree. The reason for this may be a backlash against IBM (due to royalty demands) or that video card vendors were not satisfied with the suggested standards.
For a more detailed discussion of VGA, see 'What is VGA, and how does it work?'
The 8514/a was the next graphics offering from IBM and provides three new video modes that are not available from the VGA controller. Computers with 8514/a hardware must also have a VGA controller, as the 8514/a does not support VGA video modes. The additional modes are:
Type Pixel Max. # Colours Characters
Addressability
gfx 640x480 256 80x34
gfx 1024x768 256 85x38 (interlaced)
gfx 1024x768 256 146x51 (interlaced)
The 8514/a also has some smarts, as it is capable of performing video memory transfers, drawing lines and extracting rectangular areas of the display image. These are so-called accelerated features.
The XGA has superseded the 8514/a. It was the first IBM display adapter to use VRAM, and can be configured with 500k or 1 Meg. Like the 8514/a, the XGA has accelerated features which make it faster than standard VGA for some operations. The new modes XGA introduced are:
Mode Type Pixel Max. # Colours Characters
Addressability
14 text 1056x400 16 132x25
- gfx 640x480 256/65535* -
- gfx 1024x768 16/256* -
*500k/1 Meg configurations
SVGA & UVGA
SVGA and UVGA are not established standards, and so their meanings vary depending on manufacturer. VESA VGA BIOS Extensions are the closest thing to an 'SVGA' standard. Most video cards currently available are called SVGA (Super VGA), which basically means that the card provides a superset of standard VGA calls and capabilities. This means that anything better than 640x400 and 16 colours is an SVGA mode. Some suggest that SVGA covers 800x600 modes, while UVGA (Ultimate VGA) refers to 1024x768. However, the absence of any real standard renders the term SVGA quite useless, and the term UVGA is not used frequently.
The result of having no SVGA standard is that there are many (>10 !) different SVGA chipsets available, and none of them use a common programming interface. Many provide video acceleration capabilities, which free the system CPU to do other tasks, i.e. hardware cursor, BitBlt, etc. However, to use the SVGA video modes and advanced features, each chipset requires its own driver. This is why video drivers are required for Windows 3.1, Windows 95, OS/2 & XFree86. These drivers, combined with accelerated hardware, can provide enormous increases in video performance.
If you are looking for a machine and would like SVGA capabilities, don't accept that a given video card or monitor is adequate just because it is advertised as supporting SVGA. Instead, decide what maximum pixel addressabilities and colour depths you want to use, and at what vertical refresh rates, and ensure that the models you are looking at provide those capabilities, and that software drivers are available for the operating systems and programs you will be using.
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