The 8-Bit Era's Weird Uncle: The TI-99/4A

I guess next week they're going to get to the interesting bit which is how weird the architecture actually was on that thing...

https://en.wikipedia.org/wiki/TI-99/4A

Particularly it only had 256 bytes of RAM attached to the CPU but had (I think) 16 kb of RAM attached to the video controller which the CPU could read and write through I/O registers. You could use this for non-video storage but you couldn't access it directly.

Coding in BASIC could, at the very least, hide the insanity from you.

Speaking of interesting bits, this machine isn't actually an 8-bit computer, the CPU is 16-bit. (The video controller is 8-bit though, i.e. the VRAM data bus is 8-bits. It's also the same video controller used in various other machines, e.g. MSX.)

"Bits" is a stupid measure of "computer". The TI-99/4A clearly belongs in the 8-bit era of computers.

Motorola's 68000 was the single most prolific microprocessor of the 16-bit era. Yet all the registers are 32-bit, and all the instructions easily operate on 32-bit values [1]. About the only claim to being "16-bit" is the 16-bit wide data bus.

If we go by that metric, then the IBM PC (with its 8088 hobbled by an 8-bit data bus) is clearly just another 8-bit microcomputer.

BTW, this is absolutely the way that Motorola sees it. The 68008 is just a 68000 hobbled with an 8-bit data bus, and they label it as a 8/32-bit microprocessor.

[1] And if anyone dares to point out that the 68000's ALU is only 16-bits wide, then I have bad news about the Z-80: It only has a 4-bit ALU, so I guess it's actually a 4-bit microprocessor

Well, I was gonna say this: A CPU is X bits if the highest number of bits that the value of a "load immediate" instruction can have is X. But I think this makes MIPS 16-bit.