IBM did not know what it would take for the PC to adopt. Why would IBM give any care at all about color clock?Īfter all, it grew up as a business machine many systems actually used the Monochrome Display Adapter (which had much higher resolution than NTSC) many monitors were RGBI for which color clocks did not matter, and IBM's dabble in the home market with the PCjr was a fiasco. So the business desktop market was a vacuum, avoiding perfectly useful offerings by Tandy, Commodore and Apple, holding its breath for 3 magic letters.Īll that to say, performance was not Job One. (even if that had nothing to do with it). If your mainframe or minicomputer project went sideways for any of a variety of reasons, scuttlebutt is 'this wouldn't have happened if you had bought IBM'. My dad was an IBM salesman, and there was an adage universally known: That can't be overstated - they had market dominance of (larger-than-Apple-II) computers like Google has dominance in search. The purpose of the IBM PC was to put I B M on a conservatively designed system - and let IBM's unbelievable reputation and market power sell it.

Much the opposite, they wanted to avoid at all costs cannibalizing sales of their larger and much, much more expensive minicomputer line e.g. IBM's market strategy was not to be 'Amiga', outshining the competition in raw performance. The IBM PC had the memory throughput of an Atari 2600. It has an 8-bit bus, and memory operations happened at 1/4 this frequency, at 1.19 MHz - crystal / 12. Wow, that sounds fantastic, right? IBM, big gorilla of the computer biz, comes out with a processor seemingly an order of magnitude faster than those clunky 1.02-1. So the IBM PC clock was chosen, still worshipping the color clock, at 4.77 MHz - crystal / 3. The Intel philosophy was quite different, with a fast master clock, but memory fetches only occurring at 1/4 of this speed. Mind you, all these systems above have one system clock per memory cycle. The 8088 master clock operates at 4x RAM cycle speed I can vouch that Apple did not use a 2 MHz version of the 6502 chip they used the 1 MHz version. Note that most of these systems actually overclocked the CPU. Most of the rest used 1.022 MHz - color clock / 3.5 - crystal / 14īy 'rest' I mean Apple II family, Commodore Pet, Vic, C64.The Atari 400/800 used 1.79 MHz - color clock / 2 - crystal / 8.The Atari VCS/2600 used 1.19 MHz - color clock / 3 - crystal / 12.This will come up so FYI the way you divide by 3.5 is by starting with a crystal at 4x the color clock (14.31818) and dividing by 14. Everything from the Atari VCS to the C64 made ample use of it, because some iteration of your product would inevitably need to talk to a commodity color NTSC display operating at that frequency. Back in that day, everything was built around the NTSC color clock frequency of 3.579545 MHz.

Dclock 8088