Thanks Bart; On Sat, 2007-09-08 at 10:23 -0400, Bart Trojanowski wrote: > Bill, > However, I know that RAM is not accessible by the (modern) x86 CPU until > it configures the RAM timings. When the CPU is first powered up, code > executes out of instruction cache... how it gets there from ROM I don't > really know. > That's the $64,000 question. (Dating myself.) > I am pretty sure that by the time the main BIOS code searches for the > video BIOS it's already running from a RAM (shadow or copy of ROM). > Even if the BIOS is shadowed into RAM, which is what happened on my old intel P4 and my new AMD 64 Athlon, RAM simply records an address for a ROM outside of the CPU and RAM. Where does the BIOS get those addresses and how does the CPU know how to interpret them? Are these addresses simply a fixed ISA-32 instruction? At the hardware level, a specific set of gates must be opened that lead to a bus?? that is the pathway to the ROM? > You may also want to look at MTRR registers which control how ROM is > shadowed into RAM. Thanks for the MTRR registers tip. It lead to quite a few information pages that filled in some of the details I had missed. -- Regards Bill