Whenever I talk about designers of the ZX Spectrum computer I use to say that they were smoking weed. Now I acquired one computer from another family of computers, TI99, I can tell that Texas Instruments designers not only smoked weed, but also used some heavy stuff. This is a crazy computer from an internal design view. Or maybe it was done on purpose- there was a big company behind pressing to use some obsolete chips to increase sales.

And there is the result:
TI-99/4A computer
It is a Texas Instrument TI-99/4A computer, or maybe “console”- in all technical specifications it is called console.

From a salesman point of view it is remarkable, 16 bit, 3MHz speed computer with 3 channel sound synthesizer. RAM size is a bit small, only 16K, but you can expand it!

In real world it is worse- that 16bit CPU (TMS9900) can use only 256 bytes of RAM (YES! only 256 bytes) for scratch memory and registers. All that RAM is connected to video chip and it is not directly accessible by CPU. The only path to get to video RAM is only 8 wires. Not 8 bits, but 8 wires- address and data bus are multiplexed. Also this complicated conversion from 16 bit to distant video RAM reduces computer speed to very low. And this is not only for video RAM, all user software is located in video RAM and when it is running, it takes data and programs using only that bottle neck.
TI GROM chips
And it is not all. The system software is located in special GROM chips located on an 8 bit bus with a semi serial interface (address bus is multiplexed too). And even more- computers were designed to use special pseudo language (GPL) and BASIC is written not in machine code, but in GPL. User BASIC program is double interpreted: BASIC interpreter is interpreted by GPL. And it is slow.

Computers use ancient RAM chips (TMS4116). This chip uses multiple voltage power (+12V, +5V, -5V) and this complicates power supply.

All this crap made computer not very good, and the result:

Texas Instruments had high hopes for its TI 99/4, which debuted in 1979, and the follow-on 99/4A. But the machines performed poorly and the company took a $330 million write-off before exiting the home computer market.

Losing 0.3B$ is quite big, but the company got a government contract for educational calculators and is still holding a monopoly for it and getting lots of money.

TI-99/4A block diagram

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