Some info on the 99/4As.
The white version is a later version which incorporated a new GROM (v1.1, I believe) which detects and disables unauthorized cartridges. The black and silver one does not do this. Although I believe the v1.1 console had some added routines available -- I heard this in my old TI users group, but I have not been able to find documentation to back this up.
As for the 16-bit CPU, unfortunately the 99/4-series is powered by the TMS-9900 (the same CPU used in some missile defense systems, BTW) which is a 16-bit CPU. There's even a way to add 16-bit RAM which is much faster than the 8-bit buss. However, TI decided to compete with Commodore and Atari and crippled the system to keep pricing points down. Sad, really, as a fully built system was quite a machine. The Peripheral Expansion Box alone added immense expansion capabilities without the side-car mess. (Other than that stupid PEB interface and thick fire hose cable.)
If you think the problem with the A500's side-car expansion was bad (show of hands, how many people built an extension to their desk?) you should see some of the pictures of a heavily expanded 99/4 system. WOWSERS!
The TI has a similar architecture to the Amiga in that the VDP (video display processor) and sound processor had dedicated memory (16k, although I recall that there we plans for a 64k capable VDP.) It had what I guess you could call a software blitter that controlled sprites and sound via interrupt. You could set up a list of sound commands, set a pointer, and the computer would play music with little overhead.
Unfortunately, TI decided to put TI BASIC working memory in VDP RAM, to which the CPU had no direct access. On top of that they wrote TI BASIC in GPL (Graphic Programming Language) which was interpreted. So TI BASIC was doubly-interpreted, adding three unnecessary layers of slowness. The CPU only had direct access to 4k of memory out of a 64k address space which it used mostly for scratch and registers. {bleep}s.
The CPU has 16 RAM-based registers, which is REALLY neat to experiment with multi-tasking. No need to push registers onto the stack for a task switch, you just tell the CPU where to find its registers and make sure you're keeping track to find your way back. (Simplistic, but that's the gist.)
I'd be interested in the white TI if it were NTSC. Definitely a neat console (I have three working silver and blacks here) and about 200 cartridges. Sorry I got so off-topic... :-D
