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Top Document: Atari 8-Bit Computers: Frequently Asked Questions
Previous Document: 13.11) What is the difference between NTSC and PAL machines?
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13.12) Is the software for the Atari 8-bit computers "TV-standard

{some PAL demos flicker, or won't run at all on NTSC machines}

mailto:buesch@srv.net (Brent Buescher, Jr.) writes:

This is because PAL machines have a vertical refresh frequency of 50hz
(NTSC use 60hz) which translates into more vertical blanking time for
demos and other computation-intensive graphics software.  So PAL demos
that won't work on NTSC machines are usually returning from a VBI
(vertical blanking interrupt) too late.  Some also attempt to use more
vertical resolution ("longer" display lists) than an NTSC display can
handle.

mailto:thor@math.tu-berlin.de (Thomas Richter) adds:

Yes, it is. Mostly because the frequency of the vertical blank interrupt
is different (60Hz for NTSC, 50Hz for PAL). The old OS A was not clever enough
to notice the difference, so all system timings like the keyboard auto-repeat
function depend on the TV system. These parts of the OS have been corrected
with OSB and the XL versions of the OS. However, as most games install a
VBI, their timing does still depend on the frequency -> they will run
slightly slower for PAL versions.

Another point is that the popular pseudo-colors used in the Antic-F
(Graphics 8) mode are not colorful at all when displayed on a PAL TV, because
of differences in the color encoding for the TV. The schematics of
the Xl computers include however a hack how to change the PAL version to
the NTSC version (the PAL versions include two crystals, one with 5/4th of
the frequency of the other. One is used for the system clock, the other for
the color clock), but I never dared to apply it.