On , Chris Berkhout wrote to Peter Magnusson :
CB>  PM> Of course, $F000:$0000 and $F000:$FFFF is equal to
CB>  PM> $000F0000 and $000FFFFF, the start and end of the
CB>  PM> ROM chip...
CB>         Is this code grabing data directly from the ROM chip
CB>  or is it just data from ROM that has been read into RAM ?
CB>  If data between $000F0000 and $000FFFFF were altered would
CB>  it remain different on the next boot ?
In some (not all) the actual address's of fffff through f0000 is
wired to ram and to rom. The address's for rom's are also duplicated
at the top of physical memory (address depending on processor).
During a hardware reset the processor goes to the last paragraph
of memory (respectivly) and usually gets a jump vector into the
bios rom proper. This duplication is wired into the chipset at
a hard/reset. If set that way, the bios is eventually copied into
the ram at f0000 to fffff and the chipset switches addressing to
it. Many times the chipset will also deny a write to this memory
area to protect the bios once it has been copied. Many bios's
offer the option of copying extention roms for VGA a other
unsavery items. :)
It's a good idea to exclude known bios area's that are copied to
ram from memory managers.
If your gonna do copy of rom to a file it's fairly easy to do from
debug. I would disable the bios "shadowing" before hand.
Glen...
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