23 Jan
2007
23 Jan
'07
2:04 p.m.
Tony Duell wrote:
I agree it would have been nice, except it wasn't available when the PC
was being designed. Heck, the 8087 which appeared *before* the 8089
wasn't even available.
I wrote the 8087 support for the IBM Fortran compiler (actually a set of
library routines) to prove to IBM management that there was benefit to
having the 8087 as an option (they actually wanted to remove the
socket). And they needed something that would actually *use* the 8087.
One thing that
IBM did that really toasted me back then was messing
up on the 8237 DMA controller hookup such that memory-to-memory DMA
didn't work. It could have made the whole business of extended
memory use a lot simpler.
I still think they should have used the 8089 'I/O coprocessor' which was
essentially a fancy DMA chip. That would have, for example, allowed DMA
transders to cross page bounadaries.
OK, there necver was an 80289 (or whatever), hut you
can bet Intel would
have made one if there'd been a demand (read : It would have gone into
the IBM PC/AT).
The '286 was messed up enough that no one wanted to add additional junk
and risk the PC/AT schedule. Intel was doing well enough just trying to
get a working '286 going (and caused enough delays that IBM was *not*
happy) and it still shipped with "broken" '286 chips. Ahh, I remember
the sigma-sigma marked '286 chips! :-P
--
TTFN - Guy