TI-99/4A: the first 16-bit home computer

01What you'll learn

• What is inside the TI-99/4 and 4A: processor, memory, video, sound, speech — with exact numbers.
• Why a 16-bit processor did not make the machine fast: the buses and the GPL language.
• What the TMS9918A video chip can do and what it cannot (for example, 4 sprites per line).
• Which games are well documented and what we actually know about them.
• How the price war with Commodore leads to the end of the TI-99/4A in 1984.
• How to run a TI-99/4A today: Classic99 or MAME.

02Before you start

• No prior knowledge needed — knowing what a processor, RAM and a bus are is enough.
• Optional: a Windows computer for the Classic99 emulator 🔒 local or for MAME 🔒 local.
• TI's system ROM files and games have owners. Use only those you are entitled to use.

03Steps

1. The machine at a glance

   The TI-99/4A is a computer in a single case: motherboard, ROM cartridge slot and keyboard. The power supply is external, and it connects to a television through an RF modulator. Why it matters: the TI-99/4 is the first home computer with a 16-bit processor, but its architectural quirks — listed below — take away much of that advantage.

   Parameter	TI-99/4 · TI-99/4A
   Launched	TI-99/4 — October 1979; TI-99/4A — 1981 (sources give May or June)
   Processor	TI TMS9900 · 16-bit · 3 MHz
   Memory	256 bytes of scratchpad RAM on the 16-bit bus · 8 KB system ROM · 16 KB video RAM (outside the processor's address space) · 32 KB expansion card (sold separately)
   Video	TMS9918A · 256×192 bitmap · 16 fixed colours (15 visible + transparent) · 32 sprites
   Sound	TMS9919 (equivalent to the SN76489) · 3 tones + 1 noise
   Speech	optional module (LPC synthesis)
   Language	TI BASIC in the built-in ROM
   Launch price	TI-99/4: $1,150 including a monitor · TI-99/4A: $525 (historical prices)
   Total shipped	about 2.8 million (until the end in 1984)

   ⚠️

   Why the TI-99/4 did not sell

   Reviewers complained about the keyboard and the lack of lowercase letters, expansion options and software. The TI-99/4 has a calculator-style keyboard and cost $1,150 including a monitor; according to Wikipedia fewer than 20,000 were sold by summer 1981. The TI-99/4A has a full-travel keyboard and cost $525 — roughly half.

2. The TMS9900 and 16 bits through an 8-bit bus

   The TMS9900 is a single-chip version of the TI-990 minicomputer. Its registers live in memory: switching to another register set takes a single pointer (the workspace pointer), which suits a minicomputer running many tasks. In the TI-99 only 256 bytes of scratchpad RAM and the 8 KB system ROM sit on the 16-bit bus. The rest of the RAM is on a second, 8-bit bus and is reached through the video processor.

   ✅

   Rule: a 16-bit processor does not mean a 16-bit system

   User program data is read over two machine cycles, which according to Wikipedia halves the speed. According to the TI manager who oversaw the TMS9900's development, this cancels the advantage of a 16-bit processor. We publish no "times faster than the 6502" figure — we have no source for one.

   To hide the complexity TI created the pseudo-assembly language GPL (Graphic Programming Language) — a compact 8-bit language that the processor interprets. Programs on ROM cartridges were written in GPL (which is why they are also called GROMs). TI BASIC is also written in GPL and on the Creative Computing Benchmark runs at roughly half the speed of an Apple II.

   🔒

   A closed architecture

   At launch TI released no editor, assembler or technical documentation; the official Editor/Assembler package was announced in 1981 and released in 1982. The reviewer Jerry Pournelle put TI's attitude this way: the company "worked very hard at keeping you outside the machine". TI wanted to be the sole publisher of software — and that starved the game library.

3. Graphics, sound and speech

   Video: the TMS9918A supports text and graphics modes and hardware sprites. There are 32 single-colour sprites (8×8 or 16×16 pixels, magnifiable ×2), but at most 4 on a single scan line. The palette is fixed — 16 colours, 15 visible and one transparent. The 256×192 mode is a bitmap, but it is not reachable from TI BASIC. In TI BASIC only the 32×24 character graphics mode is available, and sprites need Extended BASIC (a cartridge). The chip was also sold to other makers: ColecoVision and the SG-1000 use it, and an earlier model is part of the MSX standard.

   Sound: the TMS9919 — 3 tones and 1 noise channel (white or periodic), the same as the SN76489 used in many other machines.

   Speech: TI was a pioneer in speech synthesis with its LPC chips (from the Speak & Spell toy). A plug-in module was available for the TI-99/4 and 4A; it uses LPC (linear predictive coding) and has a small built-in vocabulary. According to Wikipedia, speech modules were offered free with the purchase of some cartridges; games with speech include Parsec and Alpiner. In Alpiner the voice is male and female and can be sarcastic when you make a bad move.

   💡

   When did the speech module appear?

   The old version of this lesson said "1982". We found no reliable source for the year, so we do not state it.

4. TI BASIC and Extended BASIC: a short program

   TI BASIC follows the ANSI Minimal BASIC standard (based on Dartmouth BASIC), not Microsoft BASIC. It is not fast, but it is accurate with numbers. The sprite and motion commands come with the TI Extended BASIC cartridge. The example defines a character, shows it as a sprite, sets its motion and plays three tones.

   TI Extended BASIC · sprite and sound (not run ⚠️)copy

   100 REM TI EXTENDED BASIC
   110 CALL CLEAR
   120 CALL SCREEN(2)
   130 REM CHARACTER 65 = SMILEY FACE
   140 CALL CHAR(65,"3C4299A1A199423C")
   150 REM SPRITE 1: CHAR 65, COLOR 16, ROW 100, COL 100
   160 CALL SPRITE(#1,65,16,100,100)
   170 REM MOTION: ROW SPEED 10, COLUMN SPEED 5
   180 CALL MOTION(#1,10,5)
   190 REM THREE TONES: DURATION, FREQUENCY, VOLUME
   200 CALL SOUND(500,440,0,554,2,659,4)
   210 GOTO 210

   ⚠️

   Not tested live

   The listing was written from the language documentation but was not run in an emulator for this lesson — so there is no TESTED label. The old version had a line with CALL SAY that we could not confirm, and comments at the ends of lines that are not valid in TI BASIC — both were removed. To break out of the program: FCTN + 4.

5. TI's games

   Around 100 games were published for the TI-99/4A, most of them by Texas Instruments itself; the press judged the library mediocre. TI also failed to license popular arcade games such as Zaxxon and Frogger. Here are six titles with verified facts.

   Game	Year · team	What it is
   Parsec	1982 · Jim Dramis and Paul Urbanus (publisher TI)	A horizontally scrolling shooter with sixteen coloured levels; uses the speech module.
   TI Invaders	1981 · Texas Instruments	A Space Invaders clone; part of the TI Arcade Game series.
   Alpiner	1982 · Janet Srimushnam (publisher TI)	You climb six of the world's highest mountains, avoiding trees, animals and landslides; with speech. The cartridge retailed at $39.95 (historical price).
   Munch Man	1982 · Jim Dramis (publisher TI)	Based on Pac-Man; instead of eating dots the hero leaves a chain pattern behind and the goal is to fill the whole maze.
   Tunnels of Doom	31.12.1982 · Kevin Kenney (publisher TI)	A dungeon role-playing game loosely based on Dungeons & Dragons; 1–4 characters, tactical turn-based combat.
   Hunt the Wumpus	1981 · Kevin Kenney	A graphical commercial version of the classic 1973 game for the TI-99/4A.

6. Models: from the 99/4 to the unreleased 99/2 and 99/8

   Model	Year	Feature
   TI-99/4	Oct 1979	Calculator-style keyboard, no lowercase; $1,150 including a monitor; ~20,000 units
   TI-99/4A	1981	Full-travel keyboard, improved graphics; $525
   TI-99/4A v2.2 ("QI")	from Aug 1983	Title screen shows "V2.2" and 1983; rejects unlicensed cartridges; a new board with fewer chips
   TI-99/2	prototype	4 KB RAM, TMS9995 at 10.7 MHz, no colour or sound; aimed at a price under $100; cancelled in April 1983
   TI-99/8	prototype	64 KB RAM, built-in speech, UCSD Pascal; cancelled in October 1983

   Peripherals for the 4A: a floppy disk drive, an RS-232 card, a P-code card for Pascal, a thermal printer, an acoustic-coupler modem and a cassette drive. The Peripheral Expansion System (PEB) box has a steel case finished in silver.

7. Timeline: the price war

   Date	Event
   October 1979	The TI-99/4 launches — $1,150 including a monitor. It sells poorly.
   1981	The TI-99/4A launches — $525, less than half the price of the 99/4.
   1981 – early 1982	The price falls to $449.95, then to $399.95 — in competition with the Commodore VIC-20 ($300).
   1982	TI cuts the wholesale price by $100 and offers a $100 rebate directly to the buyer; the street price is about $200. Commodore matches that price in December 1982.
   January 1983	Sales peak at 30,000 a week; on 10 January Commodore cuts its prices. In February TI responds with $150, in April with $100.
   June 1983	TI announces that only cartridges with a TI-licensed lockout chip will work in the 99/4A. In some stores the price is $99.
   October 1983	After huge losses (Wikipedia cites $330 million for the third quarter of 1983) TI announces that it is discontinuing the 99/4A.
   March 1984	Production ends; about 2.8 million computers were shipped in total.

   📊

   Why they lose money at $99

   TI cannot make a profit at $99 — the machine is much more expensive to manufacture than the VIC-20. The hope is to earn from software and peripherals; but that requires everything to be TI's own — which is why the company tightly controls development and pushes outside developers away.

8. Try it yourself: the TI-99/4A in an emulator

   Two well-known paths: Classic99 🔒 local — a Windows emulator by Tursilion (Mike Brent), whose author, according to Ninerpedia, obtained permission from TI to distribute the code together with their ROM files, and MAME 🔒 local, which has drivers for the TI-99/4 and TI-99/4A. We describe the steps in general terms; we have not checked the menus live.

   1. Download Classic99 (see its Ninerpedia page) or MAME from its official site.
   2. Choose the TI-99/4A and system ROM files you are entitled to use.
   3. Start the machine. The listing above needs an Extended BASIC cartridge — add it if you have one; otherwise try only the lines without CALL SPRITE and CALL MOTION.
   ⚠️

   Not tested live

   We did not run an emulator for this lesson — so there is no TESTED label. Follow the documentation of the emulator you choose for the exact settings.
   ⛔

   Copyright

   Games and system ROM files have owners. Do not upload or distribute other people's images.

04Check

Checklist

• I know the processor (TMS9900), its clock (3 MHz) and the bus limitation (256 bytes on the 16-bit bus).
• I can explain why the TI-99/4 sold poorly and what the 4A changed (price, keyboard).
• I know what the video chip offers: 256×192, 16 colours, 32 sprites, at most 4 per line.
• I know the order: October 1979 → 1981 → price war 1983 → announcement October 1983 → end March 1984.
• I know two ways to run a TI-99/4A today: Classic99 and MAME.

Quiz

05What's next

06Sources

1. TI-99/4A (Wikipedia) — dates, prices, architecture, video, sound, speech, games, the price war, prototypes.
2. TMS9900 (Wikipedia) — the processor, the TI-990, registers in memory.
3. TI BASIC (Wikipedia) — standard, speed, Extended BASIC.
4. TI LPC Speech Chips (Wikipedia) — TI's speech chips.
5. Games (Wikipedia): Parsec · TI Invaders · Alpiner · Munch Man · Tunnels of Doom · Hunt the Wumpus.
6. IEEE Spectrum: the story of the TMS9900 (Walden Rhines) — an insider's view of the processor decision.
7. Thierry Nouspikel: the internal architecture of the TI-99/4A — details on the buses and GPL.
8. Classic99 (Ninerpedia) 🔒 local — about the emulator.
9. MAME 🔒 local — the emulator with drivers for the TI-99/4 and TI-99/4A.
10. ti994.com · 99er.net 🌐 global — community archives and documentation for the TI-99.