At 08:55 AM 1999/03/03 -0600, Ryan McGarry <[EMAIL PROTECTED]> wrote: >Actually, the 8088 ran at slightly over 8 MHz. The 8086, an earlier >version, ran at 4.77. An 8088 was my first computer... Ah. Memories. > >Ryan McGarry Actually, the IBM PC ran at 1/3 of 14.31818 Mhz, approximately 4.773Mhz. That crystal frequency was selected because it could be divided by 4 on the Color Graphics Adapter (CGA) to provide the TV color burst frequency 3.58Mhz and by 3 to be under 5Mhz, because IBM used 5Mhz-rated 8088 chips. The clock was further divided for several other functions, including serial port rates, system timers, etc. I owned an original IBM PC (64KB motherboard) for 15 years, and studied the clock circuitry well enough early on to split the clocks and hop the cpu up to 7.6 Mhz while leaving the 14.31818Mhz bus line & serial ports etc unaffected, after selectively desoldering a few 74xxx chips from the motherboard and replacing them with socketed 74ALSxxx equivalents and getting an 8Mhz NEC V20, while still using the 250ns soldered-in DRAM. There were multiple speed grades for each processor. The 8086 reached 10Mhz. The 80286 had grades from 4 to 16Mhz or higher; the 386 from 12.5 to 40Mhz; the 486 from 25 to 133, and the Pentium from 60 to 233. (Not all from Intel, and perhaps I have missed a speed grade here and there.) >1977: 1Mhz 6502 or 4Mhz Z80 (also the Vax 11/780; Mhz?) >1981: 4.77Mhz 8088 in the IBM PC >1984: 6Mhz in the IBM AT (and later, IBM released other models of the AT including an 8Mhz clock) Ken ________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm
