shadowing video

[Conrad Canterford]

On Fri, 2002-11-01 at 09:16, James McNeill wrote:
> Do forgive my ignorance, but I thought that shadowing was puerly to try 
> and improve performance. My understanding was that the BIOS bus was sub 
> standard so by copying BIOS functions into RAM it could be accessed faster.
> I've never looked into it more than that. Can anyone explain the 
> technics behind why it's bad to shadow?
> -James

As I remember my days of playing with hardware: The bios is stored in a
ROM (more likely nowdays a PROM, actually, but I believe the reason
still stands). ROM's are notoriously slow to read compared to RAM (and
especially compared to modern fast RAMs). Therefore for windows boxen
who do use their bios, it is a speed-up to move the bios code into RAM.
This doesn't apply to Linux boxen, 'cos we're sensible and don't use
BIOS routines to achieve anything beyond the initial bootstrap.

I was under the (mis?)aprehension that Linux boxen still used video BIOS
routines, and that therefore a RAM shadow of video BIOS was still a
speed-up for linux. Debian obviously don't think so.

Conrad.
-- 
Conrad Canterford  (conrad at mail.watersprite.com.au)
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