alt Hacker NewsI 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.
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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.)
As I recall at the time, very few people knew how to write assembly for that machine, as there just wasn't a lot to go on.
I enjoyed the sprites though, and that was something that was definitely different than Apple II, IBM, etc. at the time. Apple and IBM's graphics were definitely a step down.
C64 could do sprites with POKE statements apparently. But that was definitely not as nice as the TI.
"Coding in BASIC could, at the very least, hide the insanity from you."
Except TI-BASIC is a hell-riddled double-interpreted language. I had a 99/4A at the age of 6, learned how to use all of the TI-BASIC language by 8, and said screw that, hardware it is for me, dad's buying me a 286 for Christmas, time to learn how to build that!
It gets way weirder.
The TMS9900 didn't have any internal data registers. It only had a program counter, a status register, and a workspace pointer. Instead, it put the "registers" in that same 256 bytes of RAM. There were sixteen 16-bit registers which the workspace pointer pointed to.
The original idea was that this made for fast context switches, instead of dumping all registers to stack (it doesn't even have a stack pointer), just update the workspace pointer to point at a new set. But I have to assume this wasn't really used on the TI-99/4A, as there just wasn't enough RAM. Because your only other ram was locked behind the video controller, that 256 bytes had to contain all your registers, any your dynamically loaded code and any data you wanted rapid access to.
The TMS9900 is weird, because it's the only CPU of the early home computer era that wasn't designed for microcomputers. It's actually an implementation of the TI-990 mini-computer on a single chip and is actually used in later versions of the minicomputer. Those minicomputers had more than enough fast 16-bit memory to take advantage of this fast context switching.
Every other commonly used microprocessor of the 70s (8080, 6800, F8, 6502, RCA1802, Z80, 6809, 8086, 68000) was explicitly designed to target the low-cost microcomputer market.