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So the video chip functioned as a sort of memory controller? I've heard of people using modern GPUs to store arbitrary data. But that was just because it's ther

So the video chip functioned as a sort of memory controller? I've heard of people using modern GPUs to store arbitrary data. But that was just because it's there, it's fast and it is not in use most of the time. But this is different.

II2II 4y ago
It probably isn't as crazy as it sounds. Graphics consumed a considerable amount of the memory on early personal computers. It looks like one of those video modes could consume about 75% of the 16 kB. Of course, that is cherry picking the most memory hungry mode. Other modes would use less memory, leaving unused memory for programs to use. If anything, it looks like the TI-99/4A is different since it appears to be designed for programs to use video memory because it's there and offers very little dedicated memory for the CPU.
nsxwolf 4y ago
Yes, that chip was the TMS9918A and it was also used in systems like the MSX computers and the Colecovision game console. The Colecovision was similar in that it offered 1KB of "scratchpad" RAM the CPU could directly address, and 16K of video RAM shared with the VDP. The chip used auto-incrementing address registers that would allow a CPU to read from and write to VRAM.