38 Should I have BIOS shadowing on?
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).
38 Should I have BIOS shadowing on?
The code which tells the computer how to access the video card is stored on the video card itself in a ROM (Read Only Memory) chip. When the computer wants to access the video card, it uses the video BIOS (Basic Input/Output System) routines on the ROM chip(s). The only real problem with this is that ROM chips run more slowly that traditional DRAM which is used for main system RAM. As a result, most (if not all) modern BIOS setup utilities (sometimes referred to as CMOS) allow the video BIOS to be copied to a section of main system DRAM (this is the shadowing). This has the benefit of speeding up video operations between the CPU and video card because the video BIOS 'instructions' can be read more quickly from the shadow RAM, and the disadvantage of using a relatively small block of upper memory (the chunk of memory is located above 640k and below 1 Meg).
When video BIOS shadowing is turned off, some systems and memory managers allow you to use that chunk of memory to load TSR's (i.e. mouse driver, cdrom driver) which may allow you to free up some additional conventional memory. When turned on, video operations will be performed faster, at the expense of a chunk of upper memory. Unless you're tight for upper memory or have a compatiblity problem, try running with shadowing on.
Continue to:
My Books
