Aspect ratio differences (NTSC, PAL, Dragon-CoCo)?

[Starscream]

I'm currently learning and experimenting with modelines for emulator output (so far only tried MESS) on CRT TV and monitor, and I was wondering if there a major differences because of the different signals, timings etc, that normally would need to be taken into account for an accurate display? E.g. I suppose a 320x240 @ 60 Hz modeline (or 120 Hz on VGA monitor) is sufficient for the NTSC CoCo and Tano Dragon, where I assume that the actual 256x192 is also usually displayed in 4:3 or very close to it. Does PAL have the same ratio, and do the machines behave all the same?

[sixxie]

I know this is an oldish post, but I happened to do the calculations the other day based on 228 cycles per scanline and what's generally thought to be the active area of 4x3 TVs. You basically end up with close to "square" pixels - one of NTSC/PAL had an pixel aspect ratio slightly over 1, the other was slightly under. I didn't consider it worth adding scaling for that in emulation!