[Cockbrand]

The pixels were actually rectangular. Imagine that 640x400 has square pixels (which it pretty much does on a then-contemporary screen). When you have half the amount of vertical pixels at 640x200, you can either have square pixels at half the image height, or double the height of the pixels (making them rectangular) and fill the entire vertical space.

[zozbot234]

CRT TV screens and monitors come in a 4:3 aspect ratio, so you need 320x240 or 640x480 for a "true" square pixel grid. (Unless you manually adjusted the horizontal and vertical stretch on the monitor to letterbox the image, but very few people would've done that). None of the common screen resolutions on the Amiga matches that exactly, though the 320x256 and 640x512 (interlaced) PAL resolutions were reasonably close for casual purposes.

[Cockbrand]

> were reasonably close for casual purposes.

That's pretty much what I was going for.