Texas Instrument TI 99/4A

The TI 99/4A is a pretty unusual computer. It is the oldest computer in my collection (1981) but at the same time it is technically a 16-bit computer! (it hosts a 16-bit TMS9900 CPU running at 3.0 MHz). It has a very uncommon peripheral support: peripherals would be connected serially to the console and each other, in a ‘daisy-chain’ fashion – a very weird look if you had it fully loaded. But that is not all… The TI has many more unusual features: support of cartridges (“Solid State Software”), Speech Synthesizer support (you can see mine in the picture), an early “Plug and Play” hardware model and many specialized chips for sound and video (similar to the MSX model).

As you can see in the pic, I have both 99/4A models: the original black/aluminum model and the plastic beige one. I prefer the original one not only because it looks better but because the keyboard feels tighter. This is a pretty easy to find computer (eBay has loads of it) but finding ones in very good condition might be a bit of a challenge.

Cartridges are also easy to find and not very expensive. Disk drives are a bigger challenge since you will need a Peripheral Expansion Box (“PEB”) which is bulky and not so easy to find. Cassette support is available and probably the best way to go if all you need is to save your own programs. As far as video goes, all you need to do is to find a RGB to Composite cable (like this one) which will give you greatly superior quality compared to RF.

Overall this is a great piece of personal computer history and a fun computer on its own.

Technical specs:

NAME   TI 99 / 4A
MANUFACTURER   Texas Instruments
TYPE   Home Computer
YEAR   1981
KEYBOARD   QWERTY full-stroke keyboard, 48 keys
CPU   TI TMS 9900 (with 256 bytes ‘cache’, actually it accesses to 256 bytes of RAM)
SPEED   3,3 MHz
CO-PROCESSOR   TMS 9918 (TMS 9929 in Europe) – Video / Sprite
RAM   16 KB – Memory expansion card can be added : 4 KB or 32 KB (up to 52 KB)
VRAM   16 KB
ROM   26 KB  : 8 KB ROM connected to the CPU + 18 KB ROM in byte-serial bit-mapped circuits (usually known as GROM, Graphic Only Memory)
TEXT MODES   32 x 24 (16 colors), 40 x 24 (2 colors)
GRAPHIC MODES   Multicolor mode : 48 x 64 with 16 colors
256 x 192 with 16 colors (only accesed via machine code)
Sprites (only with TI-Extended Basic)
SOUND   3 channels, 5 octaves (110hz to 55khz) and 1 noise channel (periodic and white)
SIZE / WEIGHT   38 x 25,5 x 6 cm / 2,15 kg
I/O PORTS   Tape interface, RGB video, Joystick (2), cartridge slot (Solid State Cartridge)
OS   TI’s own system, but a p-code card could be added, which gave access to the UCSD p-system and a Pascal compiler.
POWER SUPPLY   Special TI external PSU
(pins 1,2 : 16v / 1,6A — pins 2,4 : 8v / 0,15A)
PRICE   £99 (UK, 1983)

One thought on “Texas Instrument TI 99/4A

  1. Kevan Coleman says:

    I used the TI-99/4A for 7 years. Started with the basic machine and THOUSANDS later had a system that could hold it’s own. I grew up, had a family and moved on to the PC, but those early day’s have some very fond memories. Now computers are like toasters, cheap and un-interesting.

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