[time-nuts] 60Hz mains clocking in computers

Magnus Danielson magnus at rubidium.dyndns.org
Sun Dec 13 17:20:42 UTC 2009


Poul-Henning Kamp wrote:
> In message <4B251964.5040808 at rubidium.dyndns.org>, Magnus Danielson writes:
>> Joe Gwinn wrote:
> 
>>> The exception to this was that video generators were (and still 
>>> are) often locked to the AC line so that hum bars would not drift across 
>>> the screen.
>> I have never seen this in any of the devices I've seen. It is certainly 
>> not what we do in the TV world either. Examples would be good.
> 
> This feature disappeared with color television, specifically NTSC, which
> tweaked the vertical frequency just a tad lower than 60Hz.

That ghastly horrible 1000/1001 factor which plauge us still today. The 
PAL hack to the same problem has less withstanding effects. Whenever 
they did the HDTV standard they failed to keep the number magic of 
digital SDTV (i.e. 13,5 MHz and 18 MHz in BT.601). While that solution 
solve the technical problem, they solved in a bad way and we still 
stuffer even when the original reason for the solution have disappeared.

> Poul-Henning
> 
> PS: But NTSC gave us the 14.31818181.. MHz frequency, as imortalized
> by the ghastly colors of the IBM CGA.
> 

Most people saw CGA using RGBI monitors, so I think it is a bit unfair 
connection. Regardless, it was never the interface of precission 
colours. Things got better when IBM used the INMOS G171 for the VGA LUT 
and DAC.

Cheers,
Magnus



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