> The reason they didn’t do a full 640×480 was because they were focused on TV-compatible video hardware, not because an 8MHz 68000 couldn’t handle it.
The interleaved memory access of the CPU & Agnus means that the amount of data that can be pulled from the RAM is directly related to the bus speed.
This, combined with the horizontal line frequency and the bus width determines how many memory accesses there can be per line - to get a 640x480 progressive scan you'd have to double the amount of accesses per second and there's not enough access slots to do this at 7 MHz.
When A1200 came out (too little too late by the end of '92) with AGA the CPU speed was doubled to 14MHz with a 32-bit wide bus which finally allowed for higher resolution progressive modes, more colours etc.
Or you dual-port the VRAM. Or you have a division between RAM banks managed by the OS, e.g. “slow” and “fast.” Or you have the custom chips mediate access to the VRAM entirely, but offer a DMA feature for, say, block transfers of bits. Or…
There are lots of ways to support a full 640×480—or more—with an 8MHz 68000. Sun, Apollo, and HP all supported at least 1024×768 on their 68000/68010 workstations.
The interleaved memory access of the CPU & Agnus means that the amount of data that can be pulled from the RAM is directly related to the bus speed.
This, combined with the horizontal line frequency and the bus width determines how many memory accesses there can be per line - to get a 640x480 progressive scan you'd have to double the amount of accesses per second and there's not enough access slots to do this at 7 MHz.
When A1200 came out (too little too late by the end of '92) with AGA the CPU speed was doubled to 14MHz with a 32-bit wide bus which finally allowed for higher resolution progressive modes, more colours etc.