Bill, * William Case <billlinux [ at ] rogers [ dot ] com> [070908 09:54]: > How does the CPU know that a particular address is ROM based, located > in a different place than RAM? For example, using the above mentioned > ROM addresses does, the FFFF: or the C000: signify a specific location > for the ROMs? I am not exactly sure on this, my interest starts after CPU is executing from RAM. 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. 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). You may also want to look at MTRR registers which control how ROM is shadowed into RAM. -Bart -- WebSig: http://www.jukie.net/~bart/sig/