Dave Hart wrote:
Historically, the PC used frequencies which were convenient multiples
of the NTSC colorburst frequency, because NTSC crystals were really
cheap.
I believe it had more to do with the Color Graphics Adapter circuitry
needing to operate at NTSC-compatible frequency.l
Both, sort of:
The 8088 was spec'ed to run at 5 MHz, by taking the ~14.3 MHz needed by
NTSC and divide it by three, they ended up with 4.77 Mhz as the original
IBM PC cpu frequency. Two needs, one crystal!
(I believe the 8088 needed a 67% duty cycle, in which case they had to
start with something close to 15 MHz anyway?)
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
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