joefish wrote:Yes, it's a bit of a shame they're not square. The ZX81 / ZX Spectrum / MSX-1 / Oric have square pixels with a 256x192 display which is exactly a 4:3 ratio. On a lot of CRT TVs, that meant that their pixels aligned perfectly with the dots on the TV screen (although this could drift over time with RF modulator noise).
The ST aligns in height since the scanline spacing on a TV is the same, but in width it has 320 pixels in roughly the same space, so the pixels are squashed. Same happens with the Amiga, CPC and C64 in their equivalent resolutions.
Are you sure TVs have a standard shadow mask spacing? I thought they tended to be all over the place. Being an analogue system, they wouldn't align very well anyway. It's probably best to use a tube with the finest dot pitch you can find - I noticed a huge improvement moving from a TV to a monitor in dot pitch.
The Amiga has a different screen area aspect to the ST. This arises because it uses a 7.1MHz pixel clock - instead of 8MHz like the ST. The 320 pixels fill more of the screen horizontally, leaving a much smaller border. The Amiga also displays 256 scanlines normally - with more actual screen height than the ST.
Amiga screen width: 86%
Amiga screen height: 89%
So the Amiga has a 3.9:3 display area. However, the pixels still aren't square. They're a different kind of rectangular than the ST. If you display ST graphics on an Amiga, it will be stretched horizontally.
In order to have completely square pixels on a PAL screen, you'd need a resolution of 384 x 288 pixels (with overscan). A 320x240 display area would be 4:3 with square pixels, and would leave a decent border. The problem is, this would require a pixel clock of around 7.4MHz. That's a pretty unusual frequency, and I doubt there are many computer manufacturers who used it.
If the Spectrum really does have square pixels, the screen must be no wider than 67%. That's pretty narrow, it would leave a huge left and right border - bigger than the ST.