fjmora@CS.WM.EDU (Fredric Mora) (05/09/89)
In message dated 6 May 89 19:24:39 GMT, I.R. Gumby writes: >In article <103@sdcc10.ucsd.EDU>, cs163afu@sdcc10.ucsd.EDU (Some call me...Tim) > writes: > >> The initial release of the IBM PC AT contained a 6Mhz 8086 >> processor. It was only later that they upgraded to 8Mhz and still >> later the 286 processor. > I hate to break this to you, but Intel only manufactures 8086/8088 >chips in the following clock speeds; 4.77, 8, and 10. There was >never a 6 MHz 8086 or 8088. The Intel 80286 chips are available in >these clock speeds; 6, 8, 10, and 12 (from a company that does >subcontracting work for Intel, but these are not really Intel >chips). Harris makes 16 and 20 MHz 286's. I'm sorry, but Tim is right: The original IBM PC-AT was delivered with a 6-MHz crystal clocking an 8086 chip (and THAT's the standard, folks, 80286 AT Klones are an EXTENSION of the IBM specs), although the schematics specified 8 Mhz. I know it, I developed some hard and soft on this sorry piece of junk. My AT spent most of its time with open guts (i.e., outer case removed), so I'm pretty sure of what was inside (including Inmos RAM chips, expensive at that time.) I never heard the real reason of this clock limitation. Some said that the Intel chips were so bad that a significant percentage of the 8-MHz 8086 were not reliable at this clock speed, so IBM had to decrease the crystal frequency at the last minute. But I'll be interested in getting the straight dope if somebody believes he's got The Real Story. Now, this story seems to be confirmed by the following fact: originally, IBm planned to use the Intel 8765 floppy disk drive controller, but this chip was released with a bug (mentioned as an unconspicuous footnote in the data sheet of said chip.) So IBM used the NEC 765 instead (a compatible controller.) Regards, Frederic Mora GEnie: The College of William and Mary F.MORA Dept. of Computer Science INTERNET: Williamsburg, VA. 23185 fjmora@cs.wm.edu USA ************************************************************************** * * * "Was uns nicht toetet, macht uns staerker." * * Friedrich Nietzsche * * What does not kill us makes us stronger * * * ************************************************************************** - Come, come, little line eater, I won't harm you (evil grin)... - Come, come, little line eater, I won't harm you (evil grin)... - Come, come, little line eater, I won't harm you (evil grin)...