Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!aplcen!haven!uvaarpa!mcnc!rti!bbt!djb
From: djb@bbt.UUCP (beauvais)
Newsgroups: comp.sys.ibm.pc
Subject: Re: AMI bios
Message-ID: <508@bbt.UUCP>
Date: 17 Nov 89 23:01:13 GMT
References: <776@prles2.UUCP> <1429@starfish.Convergent.COM> <1989Nov10.200029.3693@ico.isc.com> <13225@eerie.acsu.Buffalo.EDU>
Reply-To: djb@bbt.UUCP (beauvais)
Organization: Broadband Technologies, Inc., Research Triangle Park, NC
Lines: 23

In article <13225@eerie.acsu.Buffalo.EDU> wnbell@sybil.cs.Buffalo.EDU.UUCP (William Bell) writes:
>I saw an option to change CMOS to have "Shadow RAM". I can enable
>BIOS Shadow RAm, EGA Shadow RAM, and Interleave Memory.
>Should I enable all 3 types?pes??? What does Shadow RAM mean? BIOS
>Shadow RAM seemed to speed up the CPU.

BIOS and the built in program for the low level operation of your EGA card
is stored in ROM (Read Only Memory).  ROMs are relatively slow devices, and
need to insert "wait states" to waste CPU time while they fetch the data
you requested.  RAM access is faster, usually requiring no wait states.  Many
BIOSes have a provision for copying the contents of the pokey ROMs into
speedy RAMs.  Then, circuitry is enabled which disables the ROM, and maps
the RAM (with the ROM's contents) in their place.  Thus, your CPU spends
much less time twiddling its thumbs waiting for ROM data.  

Hope this helps!

PS - BIOS and the video adapters are mapped into the space between 640K and
1024K (1 MB).
-- 
Dan Beauvais                          {backbone}!rti!bbt!djb@mcnc.mcnc.org
BroadBand Technologies, Inc., Box 13737, Research Triangle Park, NC  27709
(919)-544-6850 x 295