BCM QS750, User Manual

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4. BIOS Setup
Shadowing copies firmware from ROM into system RAM, where the CPU can read it
through the 16-bit or 32-bit DRAM bus. Firmware not shadowed must be read by the system
through the 8-bit X-bus. Shadowing improves the performance of the system BIOS and
similar ROM firmware for expansion peripherals, but it also reduces the amount of high
memory (640 KB to 1 MB) available for loading device drivers, etc.
Enable shadowing into each section of memory separately. Many system designers hardwire
shadowing of the system BIOS and eliminate a System BIOS Shadow option.
Video BIOS shadows into memory area C0000-C7FFF. The remaining areas shown on the
BIOS Features Setup screen may be occupied by other expansion card firmware. If an
expansion peripheral in your system contains ROM-based firmware, you need to know the
address range the ROM occupies to shadow it into the correct area of RAM.