larry@extel.UUCP (12/16/84)
January PC-World p16 has an ad for a new card from AST for the PC-AT. It uses 1 slot and will hold from 128k to 3.0mb of memory (user expandable), has standard 1 serial port, 1 printer port and optional second serial port and game port. It also uses a slit memory with a hole from 640k to 1mb. The thing struck me as odd was the mention of a hole in their memory addressing from 640k to 1mb. (their numbers). While this hole makes sense for a PC-DOS machine does it make sense for the AT when it is in protected mode? IBM has memory cards of up to 1mb. with no mention of such a hole. Is such a hole needed when in protect mode? Would anyone care to predict how Xenix will handle that? Larry Pajakowski ihnp4!tellab1!extel!larry
alan@drivax.UUCP (Alan Fargusson) (12/20/84)
> > > > January PC-World p16 has an ad for a new card from AST for the PC-AT. > It uses 1 slot and will hold from 128k to 3.0mb of memory (user > expandable), has standard 1 serial port, 1 printer port and optional > second serial port and game port. It also uses a slit memory with a > hole from 640k to 1mb. > > The thing struck me as odd was the mention of a hole in their memory > addressing from 640k to 1mb. (their numbers). While this hole makes > sense for a PC-DOS machine does it make sense for the AT when it is in > protected mode? IBM has memory cards of up to 1mb. with no mention of > such a hole. > > Is such a hole needed when in protect mode? Would anyone care to > predict how Xenix will handle that? > > > Larry Pajakowski > ihnp4!tellab1!extel!larry The vidio boards, and ROM are in this address range, just like the PC/XT. They have to be so they can be addressed in real address mode. I assume Xenix maps around it, since it apperently works. I assume that you cannot use any PC/XT type boards when in protected mode since they only look at 20 bits of the address, so would map to the same top of every megabyte, not just the first 640k to 1mb. -- Alan Fargusson. { ihnp4, sftig, amdahl, ucscc, ucbvax!unisoft }!drivax!alan