Posted By
Gaia
on 2005-03-29
17:03:02
|  Re: A couple of Plus/4 questions
Csabo: I have to at least partially contradict you at point 1. The answer is unfortunately not that simple 
NTSC is in fact _not_ slower than PAL, actually the opposite is true. PAL has a chrystal oscillator of 17734475 Hz while NTSC has one of 14318180 Hz. The PAL clock is divided with 10, that gives us ~1,77 Mhz and the NTSC by 8 which results in ~1,79 Mhz. So the sound oscillators and timers are running "quicker" on an NTSC machine (by the half of the appropriate freqencies on each machine).
If you blank the screen by writing 11 to TED register #6 with POKE65286,11 you get 1,70 MHz on a PAL machine and 1,71 MHz on NTSC
It is true however that most of the case (when the screen is not blanked) you have fewer CPU cycles in total, because on NTSC the screen is refreshed 60 times a second as opposed to ~50 on PAL. If you take the cycles into account that are "stolen" from the CPU because of those "dreaded" bad lines and TED graphic fetch cycles, PAL is indeed faster than NTSC: approx. 1,2 MHz against 1,1 MHz.
Well, because the clocking is partly dependant on the code executed it is a little bit trickier... how about tricks such as limiting the window area or putting a PAL machine into "NTSC mode" 
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