Texas Instruments TI-99/4A
|Release date||June 1981|
|Introductory price||US$525 (equivalent to $1,476 in 2019)|
|Units shipped||2.8 million|
|Operating system||TI BASIC|
|CPU||TMS9900 @ 3 MHz|
|Memory||16 KB RAM|
256 bytes scratchpad RAM
|CPU||TMS9900 @ 3 MHz|
The Texas Instruments TI-99/4A is a home computer released in June 1981 in the United States. It is an enhanced version of the less successful TI-99/4 which was released in late 1979. The TI-99/4 and TI-99/4A are the first 16-bit home computers, using the Texas Instruments TMS9900 16-bit CPU. Both models include hardware support for sprites, using TI's own chips, and multi-channel sound, making them some of the first home computers to include such custom coprocessors, alongside the Atari 8-bit family also introduced in 1979.
The TI-99/4A remained mostly the same as its predecessor, with the major changes being a full-travel keyboard to replace the calculator-style keys, an improved graphics chip with support for bitmap modes, and a cleaner method of adding expansion cards. The price was also half that of the original model. Texas Instruments supported the 4A with a line of peripherals, including a speech synthesizer, and a "Peripheral Expansion System" box to contain hardware add-ons.
While the TI-99/4A's specifications look impressive on paper, architectural issues keep it from reaching the performance it appears capable of. The system failed to catch on with third party developers, with the majority of games and other software created and sold by TI. A price war with Commodore's VIC-20 resulted in 99-4/A prices dropping below US$100. Despite the increased user base created from selling large numbers of systems and peripherals at heavy discounts, after a US$330 million loss in the third quarter of 1983 Texas Instruments announced the discontinuation of the TI-99/4A in October 1983, and stopped production in March 1984.
The TI-99/4A is a self-contained console with the CPU, motherboard, ROM cartridge slot, and full-travel keyboard in the same case. An external power supply varies with the country of sale, and an RF modulator allows using a television as a monitor. The system displays lowercase letters as smaller capitals, instead of separate glyphs.
TI BASIC is built-in. It's an ANSI-compliant BASIC interpreter, based on Dartmouth BASIC, with additions for graphics, sound, and file system access. Unlike most BASICs, only one statement is allowed per source line.
Peripherals include a 5¼" floppy disk drive and controller, an RS-232 card comprising two serial ports and one parallel port, a P-code card for Pascal support, a thermal printer, a 300-baud acoustic coupler, a tape drive using standard audio cassettes as media, and a 32 KB memory expansion card.
Later versions of the 99/4A, identified by
(C)1983 TEXAS INSTRUMENTS V2.2 on the title page, remove the ability to use unlicensed ROM-based cartridges, locking out third-party manufacturers such as Atarisoft.
Both TI-99/4 models use the 16-bit TMS9900 CPU running at 3 MHz which is based on TI's TI-990 minicomputers. Although the CPU is a full 16-bit processor, only the system ROM and 256 bytes of scratchpad RAM are available on the 16-bit bus. All other memory and peripherals are connected to the CPU through a 16-to-8-bit multiplexer, requiring twice the cycles for any access and introducing an additional 4-cycle wait state.
Only the program counter, status register, and workspace pointer registers are on the chip. All work registers are kept in RAM at an address indicated by the workspace pointer, with 16 registers available at any given time. A context switch instruction changes to another workspace without having to save and restore the registers. Workspaces are kept in the 256 bytes of scratchpad memory.
Video display processor
Graphics in the 99/4A are generated by a TMS9918A Video Display Processor (VDP), with a variant for PAL territories. The VDP was developed by Texas Instruments and also sold independently, allowing it to be used in other systems. It serves as the video processor for the ColecoVision and SG-1000 consoles, and an earlier model is part of the MSX computer standard.
The TMS9918A supports character-based and bitmap display modes as well as hardware sprites. There are 32 single-color sprites total, but only a maximum of 4 can be displayed per scan line. Each sprite is either 8×8 or 16×16 pixels and can be scaled 2x to 16x16 or 32x32.
16 kB of RAM is provided for the Video Display Processor. VDP RAM is the largest block of writeable memory in the unexpanded TI-99/4A architecture, but access to it has to go through the VDP as an intermediary. It is used for storing disk I/O buffers and for TI BASIC user programs. All accesses to the VDP system are executed eight bits at a time.
All TI-99 models have device drivers built into ROMs in the hardware. When a new peripheral is attached, it is immediately available for any software which wants to use it. All device access uses a generic file-based I/O mechanism, allowing new devices to be added without updating software. The system supports four RS-232 ports and two parallel printer ports.
The computer supports two cassette drives through a dedicated port. Composite video and audio are output through another port on NTSC-based machines, and combine through an external RF modulator for use with a television. PAL-based machines output a more complex YUV signal which is also modulated to UHF externally.
Two digital joysticks can be connected through a single DE-9 port. It's identical to the Atari joystick port, but with incompatible pins. Aftermarket adapters allow the use of Atari compatible joysticks.
TI sold an official 32 kB RAM expansion. The memory is not available to all uses. For example, an Extended Basic program is restricted to using 24kB with the remaining 8kB available for machine code routines. The Mini Memory plug-in module contains 4kB of battery-backed RAM that can be used as a persistent RAM disk or to load a machine-code program.
Peripheral Expansion Box
The TI-99/4A can be upgraded via expansion cards added to an eight-slot, external chassis containing its own linear power supply and a full-height 5¼" floppy bay. Encased in silver plastic, but made from sheet steel, this is labeled as the Peripheral Expansion System by TI, but usually called the Peripheral Expansion Box or PEB. Each card has an LED that blinks or flickers when being accessed by software. The section of the power supply that powers the card slots is unregulated. Each card has on-board regulators for its own requirements, which reduces power consumption on a partially-loaded PEB, allowing for cards with unusual voltage requirements.
The PEB carries an analog sound input on the expansion bus, allowing the Speech Synthesizer's audio to be carried through the console to the monitor. The audio is also carried through the ribbon cable to the PEB, both allowing the relocation of the Speech Synthesizer to the PEB and the possibility of audio cards offering more features than the console's built-in sound. No official cards from TI do this.
In the late 1970s and early 1980s, TI was a pioneer in speech synthesis because of its Texas Instruments LPC Speech Chips which were used in its Speak & Spell toys. A plug-in speech synthesizer module was available for the TI-99/4 and 4A. Speech synthesizers were offered free with the purchase of a number of cartridges and were used by video games such as Alpiner and Parsec. Alpiner's speech includes male and female voices and can be sarcastic when the player makes a bad move.
The synthesizer uses a variant of linear predictive coding and has a small in-built vocabulary. The original intent was to release small cartridges that plugged directly into the synthesizer unit to increase the device's vocabulary. However, the success of software text-to-speech in the Terminal Emulator II cartridge cancelled that plan.
In 1977, groups within Texas Instruments were designing a video game console, a home computer to compete against the TRS-80 and Apple II, and a high-end business personal computer with a hard drive. The first two groups merged at TI's consumer products division in Lubbock, Texas. According to Wally Rhines, the 99/4's "ultracheap keyboard" (with calculator-style keys), RF modulator, and ROM cartridges came from the console design. Others within the company persuaded the Lubbock group to use TI's TMS9900 CPU. The system only supported uppercase characters.
TI (because of its role as a major electronics manufacturer, defense contractor and semiconductor producer) was much larger than any other personal-computer company when it entered the market in 1979 with the TI-99/4. David H. Ahl called it "vastly overpriced, particularly considering its strange keyboard, non-standard Basic, and lack of software". Adam Osborne reported in July 1980 that despite poor sales TI had raised the price of a complete system to $1,400, making the computer more expensive than the popular Apple II, which was available for as little as $950. "Some dealers, who have offered the complete system (including the monitor) for less than the price of the Apple, have still been unable to sell it", he added. TI sold fewer than 20,000 computers by summer 1981, less than one tenth Apple or Radio Shack's volume; even Atari, Inc., which reportedly lost $10 million on sales of $13 million of computers, had an Atari 8-bit family installed base more than twice as large.
Two years after the 99/4's debut, TI released the 99/4A, very similar, but with a better keyboard and more expansion options. By lowering its price and offering rebates TI sold many more computers.
In 1982 TI lowered the street price of the 99/4A to $200, including a $100 rebate, to compete against the $300 Commodore VIC-20. TI spokesman Bill Cosby joked how easy it was to sell a computer by paying people $100 to buy one. By mid-1982, Jerry Pournelle wrote that TI was "practically giving away the TI-99/4A". An industry joke stated that the company was losing money on each computer, but was making up for it in volume. The 99/4A's list price was $400 that autumn, with a street price, including $100 rebate, of $200. Commodore matched the $200 price in December 1982.
Sales peaked at 30,000 a week in January 1983, but on 10 January 1983 Commodore lowered the price of its computers. In February TI responded with a 99/4A retail price of $150. In April, the VIC-20's bundled retail price reached $100 and the 99/4A followed suit. In the spring of 1983, TI attempted to reduce the parts count to maintain a competitive edge by combining multiple chips into a single custom chip, renaming the 4A PCB as a "QI" (Quality Improved) board and began production of plastic beige cases without the former aluminum trim of the back console. In May, it began offering the PEB for free with the purchase of three peripherals. In August the company reduced prices of peripherals by 50% and offered $100 of free software; in September, it reduced software prices by up to 43%.
The president of Spectravideo later said that "TI got suckered by" Jack Tramiel, head of Commodore. TI was forced to sell the 99/4A for about the same price as the VIC-20, even though it was much more expensive to manufacture.
After TI unexpectedly announced a $100 million quarterly loss—implying a pretax loss from home computers of $200–250 million—the Times stated in June 1983 that Cosby's $100 refund "joke is no longer funny", and that "future options are slim". The low price affected the 99/4A's reputation; "When they went to $99, people started asking 'What's wrong with it?'", one retail executive said. An L.F. Rothschild sell-side analyst estimated that TI had prepared to manufacture three million computers in 1983, but would only be able to sell two million.
TI could not make a profit on the TI-99/4A at a price of $99, but hoped that selling many inexpensive computers would increase sales of more profitable software and peripherals. Because such a razor and blades business model requires that such products be its own, TI kept strict control over development for the machine, discouraging hobbyists and third-party developers. A Spinnaker Software executive said that the 99/4A had "the worst software in the business", and Ahl noted that unlike other computers, it did not have "Microsoft BASIC, VisiCalc, WordStar, or any popular games". Its peripherals cost about twice as much as for other computers. TI joysticks, for example, were of poor quality and difficult to find; one reseller reported that its best-selling product was the Atari adapter cable.
After losing $111 million after taxes in the third calendar quarter of 1983, TI announced plans to discontinue the 99/4A, while continuing to sell the TI Professional MS-DOS-compatible computer. (TI stock rose by 25% after the announcement, because the company's other businesses were strong.) With another TI price cut, retailers sold remaining inventory of the former $1,150 computer during Christmas for $49. The 90 Child World stores quickly sold over 40,000 computers at a price referred to as "nearly a stocking stuffer" in a New York Times article.
A total of 2.8 million units were shipped before the TI-99/4A was discontinued in March 1984. The 99/4A became the first in a series of home computers to be orphaned by their manufacturer over the next few years, along with the Coleco Adam, Mattel Aquarius, Timex Sinclair 1000, and IBM PCjr.
Lack of third-party development
Citing Money, publisher of Kilobaud Microcomputing Wayne Green reported in August 1980 that TI planned to have only 100 applications available by the end of 1981, stating that "This tiny figure has to put a chill on the whole industry". Green's company, Instant Software, was a prolific publisher of TRS-80 software, but could not find anyone to port software to the TI. He wrote, "We understand the problems with the system and the efforts Texas Instruments made to make translation difficult".
Pournelle wrote in 1982, "TI had rightly concluded that the hobbyists and hackers were a tiny part of the market and wrongly concluded that they were therefore unimportant". Rivals were more open with information. Kilobaud Microcomputing reported that a Commodore executive promised the VIC-20 would have "enough additional documentation to enable an experienced programmer/hobbyist to get inside and let his imagination work". IBM released software and hardware technical information when the IBM PC was announced in 1981, stating that "the definition of a personal computer is third-party hardware and software".
TI insisted on being the sole publisher for the system, which many developers refused to agree to. After third-party developers' games for the Atari 2600 became very successful, TI at the June 1983 Consumer Electronics Show announced that only cartridges with a TI-licensed lockout chip would work in the 99/4A. The Boston Phoenix predicted that "most [software developers] just won't bother making TI-compatible versions of their programs", and Pournelle wrote that "TI once again tells the hobbyists to drop dead".
No official technical documentation from TI was released until the "Editor/Assembler" development suite was released in 1981, and no system schematics were ever released to the public until after TI had discontinued the computer.
- 256 bytes scratchpad RAM for the CPU
- 16 kB Video Display Processor RAM
- 32 single-color sprites in defined layers allowing higher-numbered sprites to transparently flow over lower-numbered sprites. Sprites are available at 8×8 pixels or 16×16 pixels, with a "magnify" bit that doubled all sprites' size but not their resolution. A single bit is available in hardware for collision detection, and the console supports automatic movement via an interrupt routine in the ROM. There can only be 4 visible sprites per scan line.
- 16 fixed colors (15 visible, one color reserved for "transparent" which shows the background color). Transparent is intended for the 9918's genlock which is disabled in the system.
- Text mode: 40×24 characters (256 6×8 user-definable characters, no sprites, foreground and background color only, not accessible in BASIC)
- Graphics mode: 32×24 characters (256 8×8 user-definable characters, full 15 color palette + transparent (available in groups of 8 through the character table) and 32 sprites (The only mode available in BASIC. Extended BASIC is required for sprites, and can access only 28 of them.)
- Bitmap mode: 256×192 pixels (no more than two colors in an eight-pixel row, full 15 color palette + transparent, all 32 sprites available but interrupt-based motion through the ROM routine is not due to the memory layout, not available to BASIC or the original 9918).
- Multicolor mode: 64×48 pixels (each pixel may be any color, all 32 sprites are available)
- All of the above comprise 36 layers starting with the video overlay input, then the background color, then two graphics mode layers, then a layer for each of the 32 sprites. A higher layer obscures a lower layer in hardware, unless that higher layer is transparent.
- 3 voices, 1 noise (white or periodic)
- Voices generate square waves from 110 Hz to approximately 115 kHz
- Console ROM includes interrupt-driven music playback
Roughly 100 games were published for the TI-99/4A, with most published by Texas Instruments. Some of the games released only for the 99/4A are Parsec, Alpiner, Tombstone City: 21st Century, Tunnels of Doom, and The Attack. TI Invaders and Car Wars are TI's renditions of Space Invaders and Head On respectively. Munch Man is Pac-Man, but the title character fills the maze with a pattern rather than emptying it of dots.
Tigervision offered a solution to the memory limitation of the standard cartridge slot in the form of a 24kB memory expansion cartridge that attached to the side expansion interface, emulating an expansion device. This allowed the company to implement a larger game completely in machine code, which was used for Espial and Miner 2049er. Exceltec also released two similar side cartridges: Arcturus and Killer Caterpillar.
InfoWorld criticized the computer's game library as mediocre. TI not only discouraged third-party development, including games, but it also failed to license popular arcade games like Zaxxon and Frogger.
The Hex-Bus interface was designed in 1982 and intended for commercial release in late 1983. It connects the console to peripherals via a high-speed serial link. Though it is similar to today's USB (plug and play, hot-swappable, etc.), it was never released, with only a small number of prototypes appearing in collector hands after TI pulled out of the market.
At the time they left the home computer market, TI had been actively developing two successors to the TI-99/4A. Neither entered production, though several prototypes of each are in the hands of TI-99/4A collectors. Both machines would have been substantially faster than the original TI-99/4A and used the Hex-Bus serial interface.
- TI-99/2, a 4K RAM, 32K ROM computer with no color, sound, or joystick port and a Mylar keyboard. TI designed the computer in four and one half months to sell for under $100 and compete with the Sinclair ZX81 and Timex Sinclair 1000. Based on the TMS9995 CPU running at 10.7 MHz and with a built-in RF modulator, performance greatly increased when the screen was blank. The University of Southwestern Louisiana developed system software. 99/2 software ran on the 99/4A, but not vice versa. Working prototypes appeared at the January 1983 Consumer Electronic Show (CES). Home-computer prices declined so quickly, however, that by mid-1983 the 99/4A sold for $99. The company canceled the 99/2 in April 1983, but planned to exhibit it at the June CES until other companies' press conferences there indicated that competition would increase.
- TI-99/8 and 99/6. The 99/8 reportedly had a $200 wholesale price. Privately shown to dealers but not announced at June CES, it was formally canceled in October 1983. It included 64 kB of RAM expandable to 15 megabytes, a larger keyboard, built-in speech synthesis, built-in UCSD Pascal operating environment, and the full 16-bit data bus available on the expansion port. It was abandoned in the prototype stage. The Multi Emulator Super System is capable of running what are believed[by whom?] to be the system's ROMs.
The Tomy Tutor and its sibling systems are Japanese computers similar in architecture and firmware to the 99/8. Unlike the 99/8, it was released commercially, but sold poorly outside Japan. Portions of the operating system and BASIC code are similar to the 99/8.
As of 2020, there is still an annual Chicago TI Faire where people celebrate the TI-99 family of computers.
The Myarc Geneve 9640 is an enhanced TI-99/4A clone built by Myarc as a card to fit into the TI Peripheral Expansion System. It uses an IBM PC/XT detached keyboard. Released in 1987, it is similar to the unreleased TI-99/8 system. It includes a 12 MHz TMS9995 processor, enhanced graphics with 80 column text mode, 16-bit wide RAM, MDOS, and is compatible with nearly all TI software and slot-mounted hardware. A toggle switch slows the computer to the same speed as the original.
The Second Generation CPU card (SGCPU) was released by the System 99 User Group in 1996 as a card to be installed in the PEB.
The Phoenix G2, was designed in 2010 by Gary Smith, a member of TI-User Group UK. It uses two FPGAs to emulate the entire architecture of the Myarc Geneve 9640 and the TMS9995 microprocessor. It incorporates an SD card reader, ethernet, VGA output, and 64 MB RAM.
An FPGA-based TMS9918 compatible graphics chip, called the F18A, is a drop-in replacement for the original 9918 VDP, but features VGA output, bypassing the TMS9918A's native composite output, and contains other enhancements such as removing the restriction of 4 sprites per scan line.
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|Wikimedia Commons has media related to Texas Instruments TI-99/4A.|
- Ninerpedia wiki devoted to the TI-99 series
- Hexbus TI-99/4A pictures, including prototype equipment
- TI-99/4A Stuff TI-99/4A website showing software cassettes, cartridges, and TI99 resources
- 1979 TI-99/4 the TI-99/4A's predecessor, the TI-99/4
- The TI-99/4A Home Computer Page site dedicated to the TI-99/4A: forum, links, downloads
- Mainbyte hardware projects/hacks and descriptions
- TI99ers Hall of Fame recognizes those in the TI99'er Community who have contributed to the success of the Texas Instruments TI-99/4A and Myarc Geneve 9640 home computers
- TI 99/4A Gameshelf repository of game and edutainment software
- TI-99/4A Forums active forum with many long-time TI-99/4A experts