IIRC, some of those old machines interleaved CPU and GPU memory access windows, since memory was so much faster than CPUs back then.

Edit: this is what I'm talking about: https://www.bigmessowires.com/2011/08/25/68000-interleaved-m...:

> The Atari ST and Amiga appear to have both used a more aggressive scheme where video circuitry access occurred during known dead time in the 68000 bus cycle, so the CPU never had to wait