shadowing video

[Cameron, Leigh B]

> 
> 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?
> 
"Shadowing" is putting a copy of the relevant sections of the BIOS into RAM,
and then mapping those sections to the same addresses.  This was done in the
DOS/WIN3.11 days to increase performance - reading from dynamic RAM is much
faster than reading from the EPROM where the BIOS is normally stored, hence
the speed increase.

Linux (like most modern PC OS's) uses it's own drivers for all such hardware
- the BIOS is only used to get the boot process started.   Hence the
reccomendation to switch it off - it's pointless!  (and possible even
harmful, by taking a few KB of your RAM)

Leigh.


> -James
> 
> Scott D. Ferguson wrote:
> 
> ><I've just inherited a Linux box with Debian installed.
> ><In the BIOS setting I notice that all shadowing <options 
> have been selected (including video).  <Normally (under OS/2 
> or Win9x) I would de-select <these options.
> ><What option is best (for performance) under Linux?
> >
> >Answering my own question :-)
> >
> >According to Debian documentation - best option for 
> performance is to turn off ALL shadowing (video and bios).
> >---
> >If 6 million people believe a stupid thing,
> >        - it's still a stupid thing...
> >
> >
> >
> >
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