39 Should I use a Universal VESA driver? (i.e. UNIVBE)
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).
39 Should I use a Universal VESA driver? (i.e. UNIVBE)
The Video Electronics Standards Association has produced a standard for SVGA video modes, commonly known as VESA VGA or VESA SVGA. This standard includes the ability to address video memory linearly (i.e. as one large contiguous block of memory) instead of using the 64k segments that must be used for a VGA video adapter. Additional enhancements increase the speed and efficiency of system RAM <--> video RAM transfers. Different versions of this standard are supported by various different graphics cards and drivers, but the most common are v 1.2 and most recently 2.0.
This VESA standard allows programmers to support a wide variety of video devices without having to write hardware-specific drivers. The cost of having a generic standard is that the code is rarely optimized for any given video processor. As a result, a native-mode driver will usually provide better performance that a comparable VESA mode.
The reason for this is that most vendors spend their time optimizing Windows/Win95 drivers and not BIOS modes. Software VESA drivers like UniVBE use the faster native-modes for normal BIOS calls, resulting in improved performance. The speedup is due to the fact that the video card manufacturer has not fully utilized the capabilities of the video hardware in the video BIOS.
Most new video cards have the VESA standard implemented in hardware, and support VESA calls directly, without requiring a software driver. Some older cards support an older version of the standard, or have errors and/or inefficiencies in their VESA implementation. Other video cards do not have VESA support at all.
Depending on what type of card you have, you may or may not see a speed increase by using a VESA driver. The following guidelines may help you:
If you have a new card which supports VESA 2.0, then you will not likely see any speed increase with a TSR like UNIVBE, in fact you may see a slight slow down due to extra overhead associated with the TSR.
If your card is slightly older and supports VESA 1.2 or poorly implemented 2.0, then it's quite possible that you will see a small speed increase. As an added bonus, if your VESA implementation has any bugs, UNIVBE will fix them (when it's running of course).
If your card is quite old, you may see a significant speed improvement due to the linear addressing and 16/32 bit transfers of the VESA standard. However, your card must be able to support these operations (though not necessarily support VESA modes in video BIOS). For cards that do not support linear addressing, some gains may be realized because in general the bank switching code of a software VESA driver like UNIVBE is faster than the implementation in most video card BIOSes.
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