Retro Tech: Exploring the TI-99/4A

Benj Edwards

An inexpensive but capable home computer

Famed calculator maker Texas Instruments’ first stab at the home computer market arrived in 1979 with the flawed TI-99/4, which included a poor keyboard, no support for lowercase characters, and the requirement that it use a custom TV monitor. Two years later, TI fixed those issues with the TI-99/4A (note the “A”)—seen here—which retailed for $525 (about $1,368 today when adjusted for inflation). That was pretty cheap at a time when the Apple II cost over twice that much.

TI’s revised model fared much better in the U.S. home computer market and created a fairly popular alternative to Atari, Commodore, and TRS-80 CoCo machines. Many kids in the United States grew up leaning to program BASIC on a TI-99/4A and used it to experience video games for the first time, which they could do through plug-in program cartridges. In the slides ahead, I’m going to look inside this 1980s classic and see what makes it tick.

Benj Edwards

A closer look

I’ve been collecting computers for over two decades and I have seen hundreds of machines, and yet the original black and silver TI-99/4A is still one of my favorite examples of home PC industrial design. The machine is compact and feels solid, its keyboard is welcoming, and its metal trim feels professional despite its discount retail price.

The large black area to the right of the console unit accommodates a single slide-in ROM cartridge, which plugs into the unit horizontally. The TI-99/4A was a very cartridge-centric system; hundreds of programs, from games to utilities to productivity apps were available in plug-in form. More advanced users could load programs from cassette tape or floppy disk—if they could afford such luxuries. Otherwise, cartridges did the trick quite nicely.

Benj Edwards

Cracking the case

After removing five screws from the bottom of the unit and pulling out the plastic power switch, the bottom of the TI-99/4A comes off easily. Most of the internal assemblies are screwed upside down into the top of the computer’s case.

Benj Edwards

Freeing the internal assemblies

Once inside, the first subassembly to come out is the power supply, the green circuit board seen in the lower left of the photo. I have also removed the motherboard, which is encased in heavy sheet-metal RF shielding. The green board remaining in the case is the bottom side of the keyboard assembly. This thing is built like a tank—it could probably take a good pounding from an angry kid losing at Munch Man.

Benj Edwards

Mostly apart

Here I have taken the three subassemblies (power supply, motherboard, and keyboard) out of the chassis, and now you can see the keyboard assembly sitting by itself. Look at how cute and compact the keyboard is. We’ll take a closer look at that in a minute.

Benj Edwards

Removing the shielding

Judging by the thickness of the RF shielding and how tightly it wraps around every opening, Texas Instruments must have had some trouble with RF emissions from its motherboard. Per FCC regulations, consumer electronics that might interfere with radio or TV reception must be shielded to block stray RF emissions, which are generated naturally by any active circuit. Removing all that shielding wasn’t trivial. Two large metal clips and three screws with compression-fitting nuts held it tightly together. Once it was off, however, I could finally see the motherboard in all its green, IC-laden glory.

Benj Edwards

The keyboard up close

The keyboard inside the TI-99/4A is notably small—about 8.5 inches in width and 4 inches in depth. Its small size and low key count were no doubt the product of cost-cutting measures. I personally have always lamented the TI's lack of a dedicated backspace key—that would have made typing on the computer vastly more convenient.

But, oh well—the things we take for granted these days. When I was a kid, we walked uphill both ways to school without a backspace key.

Benj Edwards

The motherboard

In this close-up of the right half of the motherboard, we see a huge IC chip (the CPU), a prominent connector (the cartridge port), and several blue patch wires running here and there. Wires like this often signify last-minute design fixes that were soldered in by hand at the factory. It’s never reassuring, in my opinion, to see them in a shipping product—but hey, it works.

On the right side of the board is the peripheral expansion bus connector, of which you can only see its copper shielding here. TI created many peripherals for the 99/4A which plugged into the right side of the computer, making for a cumbersome expansion process. Later, they released a unified expansion box to simplify things, but it was still awkward.

Benj Edwards

A unique 16-bit CPU

It may surprise many folks to learn that the TI-99/4 and 4A were the first home computers to ship with a 16-bit microprocessor. Its 3MHz TMS9900 chip was a shrunk down, integrated circuit version of the CPU in TI’s heavy-duty TI-990 minicomputer line.

Those specs might sound impressive on paper, but the CPU’s awkward architecture coupled with the 99/4A’s low-cost supporting chips meant that the whole assembly was not notably faster or more powerful than any other home computer at the time. On top of that, the 99/4A’s BASIC language was itself written in an interpreted language, GPL, which made the machine seem slow as molasses.

Benj Edwards

Playing Alpiner

When you put it all together, the TI-99/4A was a distinctive, somewhat hamstrung machine that nonetheless enjoyed a sizable following in the United States during the early 1980s. After a fierce price war with Commodore, TI released a lower-cost gray plastic model of the 99/4A in 1983, but lost quite a bit of money in the market and discontinued the platform completely in 1984.

As for me, the TI-99/4A was one of the first vintage computers in my collection, and I have always had a soft spot for it. Over the years I have gathered up dozens of cartridges, and I still love how easy it is to just plug them in and play games or use software; it seems fun, personal, and immediate in a way that other home computers often don’t. The 99/4A’s intimate feel is perhaps the machine’s greatest legacy—that and the generation of kids who became programmers by using it.

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