{"id":6444,"date":"2014-11-07T13:46:36","date_gmt":"2014-11-07T12:46:36","guid":{"rendered":"http:\/\/www.jungsi.de\/?p=6444"},"modified":"2026-09-09T10:30:26","modified_gmt":"2026-09-09T08:30:26","slug":"ti-994a-retro","status":"publish","type":"post","link":"https:\/\/www.jungsi.de\/en\/ti-994a-retro\/","title":{"rendered":"TI-99\/4A [Texas Instruments]"},"content":{"rendered":"

One of the home computers that I used to come across time and again in magazines \u2013 and which therefore stuck in my memory \u2013 but which I never actually owned, was the TI-99\/4A. Back then, when I was typing out listings from magazines such as CK (Computer Kontakt) for the Sinclair ZX Spectrum, the TI often featured in them too, with long listings. However, nobody in my circle of friends owned this computer.<\/p>\n\n\n\n

The TI-99\/4A was launched in 1981 as the successor to the TI-99\/4 and was developed and manufactured by Texas Instruments, the leading semiconductor manufacturer of the time, based in Dallas. In Germany, the launch price was around 1,400 DM. By way of comparison: a Sinclair ZX81 cost just under 400 DM in the same year, whilst the Commodore VC-20 was priced at 899 DM \u2013 so the TI was positioned well above the entry-level machines in terms of price. At the higher end of the market, however, it was still cheaper than \u2018professional\u2019 computers such as the Apple II, which cost around 3,000 DM (without a floppy disk drive) in this country. Although the TI-99\/4A was not the very first 16-bit home computer \u2013 that honour goes to its predecessor, the TI-99\/4, which was released in 1979 but saw little widespread use \u2013 it was certainly the first 16-bit computer to achieve significant popularity amongst home users. It became particularly popular in North America and Western Europe, but with 2.8 million units sold, it did not match the sales figures of Commodore, Apple, Sinclair or Amstrad. The high production costs led to substantial losses for Texas Instruments in 1983, following which production was discontinued in October of that year. Remaining stock was sold for just 50 dollars shortly before Christmas.<\/p>\n\n\n\n

The TI-99\/4A was not the first computer in this series: TI had already launched the TI-99\/4 back in 1979, which also featured the TMS9900 processor. For a price of US$1,150, you received the computer and monitor as a compulsory bundle \u2013 TI had failed to secure FCC approval for its own RF modulator in time and was therefore obliged to include a modified 13-inch Zenith colour television as the monitor; you were not permitted to connect your own television set at all. It was not until January 1980, following an FCC exemption, that the TI-99\/4 could be purchased without this monitor. With just around 20,000 units sold, it nevertheless remained a clear flop. Instead of a proper keyboard, it also featured only a button-like calculator layout with no key travel at all. For graphics, it used the TMS9918 (without the \u2018A\u2019), which, unlike the TMS9918A\/9929A fitted in later models, lacked the additional Graphics II mode \u2013 though the TI-99\/4 was already capable of 16 colours and sprites. With the TI-99\/4A, launched in 1981, TI focused primarily on improving usability and reducing costs: a full-fledged keyboard with genuine key travel, a standard RF modulator for connection to any standard television, a simplified internal design that made production cheaper, and \u2013 with the PAL-compatible TMS9929A variant \u2013 the possibility, for the first time, of operating the computer in Europe as well. However, the built-in \u2018Equation Calculator\u2019 from the TI-99\/4 was not carried over; TI removed it from the successor model without providing a replacement.<\/p>\n\n\n\n\n\n\n\n

Technical Specifications<\/strong>
Processor: TMS9900 (16-bit, 3 MHz)
Memory: 256 bytes of static RAM (CPU-internal scratchpad RAM) + 16 KB DRAM used exclusively as video memory
Graphics: TMS9929A (PAL)
Sound: TMS9919
Storage media: Plug-in modules, audio cassettes, 5\u00bc-inch floppy discs
Operating system: TI Basic, TI DOS<\/p>\n\n\n\n

One reason for the failure of the TI-99\/4A was a somewhat unfortunate hardware design, which is directly linked to the memory. The 16 KB of RAM in the computer is not freely usable working memory, but is reserved exclusively for the graphics chip. The actual CPU has only 256 bytes of its own, albeit fast, static RAM \u2013 this is where, amongst other things, the processor\u2019s working registers are located, as the TMS9900 does not have any real internal registers of its own, but operates via a workspace pointer in the RAM.<\/p>\n\n\n\n

If you want to access the 16 KB in the graphics chip, you can only do so indirectly: you must first pass a destination address to the video chip and can then read or write byte by byte \u2013 a real bottleneck, as every single access to variables or programme code takes this slow detour. In TI Basic\u2019s Graphics-I mode, at least 12 KB of this was available to you. However, machine programmes could still not be executed \u2013 the 256 bytes of CPU RAM were nowhere near enough for that, which is why you needed the PEB (Peripheral Expansion Box) with 32 KB of memory expansion, as well as a floppy disk drive with a separate controller.<\/p>\n\n\n\n

The marketing strategy also reflected this somewhat unfortunate start: the packaging deliberately did not feature the technical model designation TI-99\/4A, but simply read \u2018Texas Instruments Home Computer\u2019 in large letters. After all, the term \u2018home computer\u2019 was still new in 1981 and had to be explained to many buyers in adverts \u2013 at that time, a home computer was still a completely abstract concept for most people.<\/p>\n\n\n\n