bob@vmix.UUCP (Bob Stoll) (07/03/87)
We are creating a graphics board which needs 64K of memory space on the IBM PC and are interested in who is using what addresses. Is there a central repository for this information? Our first pass uses A000:0 to A000:FFFF but we find that this in incompatable with the VGA and EGA high resolution graphics modes. We also tried D000:0 to D000:FFFF but this crashes the machine in certain older versions of BIOS ROMS (not to mention PC clones). Any help would be appreciated.
ftp@hpcvlo.UUCP (07/06/87)
According to the info in my manuals and books, the upper memory area is
organized like this:
a000 video (EGA, VGA)
b000 video (Mono, CGA, VGA, EGA)
c000 expansion ROMs
d000 ROMs (expansion and/or BIOS, I'm not sure)
e000 ROM (usually BIOS on newer machines)
f000 ROM (always BIOS)
Seems to me you're pretty much stuck with having to somehow share the 128K
of video space with the other video cards. (CGA actually starts at b800,
while mono starts at b000, so they can both run at the same time.)
All addresses in this note are hex SEGMENT addresses.
Everett Kaser
Hewlett-Packard Co.
Corvallis, ORbrown@nicmad.UUCP (07/09/87)
In article <1610017@hpcvlo.HP.COM> ftp@hpcvlo.HP.COM (Anonymous FTP) writes:
<According to the info in my manuals and books, the upper memory area is
<organized like this:
<
< a000 video (EGA, VGA)
< b000 video (Mono, CGA, VGA, EGA)
< c000 expansion ROMs
c800 Hard Disk BIOS
< d000 ROMs (expansion and/or BIOS, I'm not sure)
But something in my mind says that this area is used
for the EMS. (The 64K page of extended memory)
< e000 ROM (usually BIOS on newer machines)
On PC/XTs it is ROM expansion
< f000 ROM (always BIOS)
ROM expansion
f600 Cassette BASIC
fe00 ROM BIOS
There just isn't 128K of area available.
--
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