The TI-99/4A was unique among 1980s computers for having a distinctly different memory architecture. The 2022 Commander x16 similarly uses IO ports to access video RAM and eliminates some bottlenecks that kind of machine had but it has generous RAM, not a pittance.
I actually used the DNOS operating system on the mini line where the 9900 originated.
I flew around the country ripping these out of industrial equipment dealerships (replacing them with SCO), so I never saw any of the DNOS networking features.
> Also, to be slightly pedantic, the X-16 doesn't have IO ports. It's using a 65C02 processor, where all I/O is memory mapped.
The video ram is not on the 65C02's bus apparently and is accessed through a set of registers which must slow down things quite a bit, you get plenty of video memory this way though I guess. Must be what they mean by "IO Ports"
The X16 has a clever trick in that it has a memory mapped register that points to the next address to write to, and a register that causes anything you write to it to be written to that pointer in VRAM… and the pointer auto increments. So if you are doing a block copy it is as fast to write to VRAM.
One advantage of this scheme is that the CPU is not sharing access to RAM with the video processor so ordinary RAM access is fast.
