Malvineous wrote:

Interesting. Is this a standard thing, that 320x200 displayed as 640x400@70Hz, different to text mode at 720x400@70Hz? Some of my old CRTs used to struggle with 640x400 but 720x400 (text) and 320x200 were always fine, so I figured they must be using the same timing on the analogue output.

I wouldn't think there'd be any difference between 640 and 720, especially on a CRT which just doesn't care about the horizontal resolution, but there's always room for video mode weirdness. Maybe your video card was mapping 640x400 to a different mode for some reason? (It's not a "standard" mode as defined in the original VGA spec.)