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The Texas Instruments TI-99/4A is a home computer, released June 1981 in the United States at a price of $525 ($1,400 adjusted for inflation). It is an enhanced version of the less successful TI-99/4 model, which was released in late 1979 at a price of $1,150 ($4,000 adjusted for inflation). Both models include support for sprites and multi-channel sound, some of the first home computers to include such custom hardware, alongside the Atari 8-bit family also introduced in 1979.

Texas Instruments TI-99/4A
1979 TI-99-4 with Speech Synthesizer, RF modulator, keyboard overlays (adjusted).jpg
1979 TI-99/4 with RF modulator, optional Speech Synthesizer, keyboard overlays, and a cartridge
TypeHome computer
Release dateJune 1981 (1981-06) (TI99/4 in October 1979)[1]
Introductory price$525 (equivalent to $1,400 in 2018)
DiscontinuedMarch 1984
MediaROM cartridge
Floppy disk
Operating systemTI BASIC
CPUTI TMS9900 @ 3.0 MHz
Memory256 bytes "scratchpad" RAM + 16 KB VDP (graphics RAM)



The TI-99/4 has a calculator-style chiclet keyboard and a character set that lacked lowercase text. The TI-99/4A added an additional graphics mode, "lowercase" characters consisting of small capitals, and a full-travel keyboard. Both use 16-bit processors, making the TI-99/4 series the first 16-bit home computers.

The TI-99/4A's CPU, motherboard, and ROM cartridge ("Solid State Software") slot are built into the keyboard. The power regulator board is housed below and in front of the cartridge slot under the sloped area to the right of the keyboard. This area gets very hot so users commonly refer to it as the "coffee cup warmer". The external power supply, which was different according to the country of sale, is a step-down transformer.

Available peripherals included 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, an acoustic coupler, a tape drive using standard audio cassettes as media, and a 32 KB memory expansion card. The TI-99/4 was sold with both the computer and a monitor (a modified 13" Zenith color televisioin) as Texas Instruments could not get its RF modulator approved by the U.S. Federal Communications Commission in time[citation needed]. The TI-99/4A did ship with an RF modulator.

TI-99/4A speech demo using the built-in vocabulary

In the early 1980s, TI was known as a pioneer in speech synthesis, and a highly popular 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 many TI-written video games (notable titles offered with speech during this promotion were Alpiner and Parsec). 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, which would increase the device's built in vocabulary. However, the success of software text-to-speech in the Terminal Emulator II cartridge cancelled that plan. In many games (mostly those produced by TI), the speech synthesizer has relatively realistic voices. For example, Alpiner's speech includes male and female voices and can be quite sarcastic when the player made a bad move.

State of the art 16 bit computer system in 1979 – a TI-99/4 console, including the rare Thermal Printer.
TI-99/4 'PEB' or Peripheral Expansion Box

The TI-99/4's original expansion concept was that peripherals would be connected serially to the console and each other, in a "daisy-chain" fashion. The "sidecar" expansion units can be connected together in a continuing chain, but can rapidly occupy an entire desktop and cause crashes and lockups due to the large numbers of connectors on the system bus.

This original idea was soon replaced by a system based on expansion cards. Encased in silver plastic, but made from sheet steel, these plug into the bulky "Peripheral Expansion System" (usually known among TI owners as the Peripheral Expansion Box or "PEB"), an eight slot chassis, containing its own linear power supply and a full-height 5¼" floppy bay.[2] Each card also has its own "access light", an LED that would blink or flicker when the card was being used by software. As on the earlier S-100 bus, the section of the power supply that powers the card slots is unregulated. Each card has on-board regulators for its own requirements, thus reducing power consumption on a partially loaded PEB and allowing for future expansion cards that might have unusual voltage requirements.

The PEB also carries an analog sound input on the expansion bus. This allows the TI Speech Synthesizer's audio to be carried through the console to the monitor. The audio is also carried through the ribbon cable ("firehose", as TI users often call it) to the Peripheral Expansion System, both allowing the relocation of the Speech Synthesizer to the Expansion box and allowing for the possibility of audio cards offering more features than the console's built-in sound. No "official" cards from Texas Instruments ever made use of this line.

Early models (the TI-99/4, identified by its keyboard and "(C)1979 TEXAS INSTRUMENTS" on the title page) includes a built-in equation calculator, but in the 99/4A ("(C)1981 TEXAS INSTRUMENTS") this feature was discontinued. All consoles include TI BASIC, a strict ANSI-compliant BASIC programming language interpreter that is largely incompatible with the more popular, and frequently imitated, Microsoft BASIC. Later consoles, identified by "(C)1983 TEXAS INSTRUMENTS V2.2" on the title page, also remove the ability for the system to execute unlicensed ROM-based cartridges, locking out third-party manufacturers such as Atarisoft.

The system has a joystick port that supports two digital joysticks, which TI referred to as "wired remote controllers". The two joysticks are connected through a single nine pin DE-9 port which is identical with those used for Atari 2600 joysticks but with incompatible pins. Aftermarket adapters were available which allow the use of two Atari-compatible joysticks.[3] The computer supports saving to, and loading from, 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.

16-bit processorEdit

The TI-99/4 series is a 16-bit personal computer.[4] The TI-99/4A has a 16-bit TMS9900 CPU running at 3.0 MHz. The TMS9900 is based on TI's range of TI-990 mini computers.

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. 16 registers are available at any given time, and a context switch instruction that changes to another workspace automatically allows fast context switches compared to other processors that may have to store and restore the registers. For CPU RAM, the machine has only 256 bytes of "scratchpad" memory to support the storage of workspaces. This memory is placed directly on the 16-bit bus with zero wait states, making it much faster than any other memory available to the system.

Although the CPU is a full 16-bit processor, only the system ROMs and 256 bytes of scratchpad RAM is 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. This is reportedly due to the failure of a new 8-bit processor being designed by TI for this system, while the 9900 processor was already in production and proven. A user modification in later years involves "piggybacking" static RAM chips onto the console's 16-bit ROM chips, allowing a standard 32kB RAM expansion without the wait state and approximately a 30% speed increase for many applications.[citation needed] Applications previously running entirely in 8-bit RAM (both code and registers) can speed up by a factor of two. Most hardware is based on the system clock, not the program execution speed, and the hardware access still runs through the 8-bit bus with the wait states intact, so this particular modification does not affect any peripherals.

The video display processor (VDP) in the 99/4 is a Texas Instruments TMS9918.[5] It lacks a bitmap mode, which was added in the 99/4A. The VDP in the American 99/4A is the TMS9918A, giving the machine the "A" in its name. In the European PAL consoles this is replaced with the TMS9929A, which also powered MSX machines.

A unique feature of these VDP chips is that they contain hardware support for superimposing on-screen graphics over other video signals. Although TI announced a peripheral card called the Video Controller Card to allow the control of select LaserDisc players, which could switch between the TI's display and the LaserDisc player, the genlock capability of the 9918 is disabled in the design of the 99/4A and requires hardware modifications to use.

All accesses to the VDP system are executed eight bits at a time. Although this affects performance, it made it easier to upgrade the VDP when newer, relatively compatible chips were released by Yamaha Corporation. Peripherals from Mechatronics, and Michael Becker, simply called "80-column cards" include the Yamaha V9938 VDP, which gives the 99/4A a top resolution of 512×424 pixels in 16 colors or 256×424 pixels in 256 colors. This also increases the VDP memory from 16K to a maximum of 192K, although only software explicitly written for the 9938 takes advantage of it.

The unusual architecture of the 99/4 series is documented[by whom?] to be due to the failure of the 9985, an 8-bit processor created specifically for the machine. When it was abandoned, the 16-bit 9900 was selected to replace it, and a great deal of "glue logic" had to be added to fit the processor into the existing design, while no changes were made to take advantage of the 9900's strengths.

"Plug and play" hardware supportEdit

Daisy-chained Hexbus peripherals

All TI-99 models, from the earliest TI-99/4 to the unreleased TI-99/2 and TI-99/8, include plug and play support for all peripherals. Device drivers (called "Device Service Routines", or DSRs) are built into ROMs in the hardware; when a new card was inserted, it is immediately available for any software which needed or wanted to use it. All device access utilize a generic file-based I/O mechanism, allowing new devices to be added without updating software to use it. The Communications Register Unit (CRU) can address 4096 devices; however, each TI card runs at a hard-wired address on the CRU bus, and so multiple cards of the same type cannot be supported without modification. The only official card known to be modifiable is the RS-232 card, which supports two different base addresses. This allows the system to support four RS-232 ports and two parallel printer ports. Four-line BBSes were being run, using properly jumpered serial cards, on TI-99/4A systems as recently as the mid-1990s.[citation needed]

Most hobbyist-created cards released after TI's exit from the personal computer business include switches to set the base CRU address.

The HexBus 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 prototypical 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. Several HexBus peripherals were planned or produced. A WaferTape drive never made it past the prototype stage due to reliability issues with the tapes. The 5.25-inch floppy drive also never made it past the prototype stage, even though it worked.[6] Prototype DSDD disk controllers and Video controllers were also made.[7] A four-color printer-plotter, a 300-baud modem, RS-232 interface, an 80-column thermal/ink printer, and a 2.8" "Quick Disk" drive were the only peripherals released in quantity, mostly for use with the Compact Computer 40 (CC-40). All HexBus peripherals can be used with a TI-99/4A when connected through the HexBus Interface, through direct connection to the TI-99/8, or through direct connection to the CC-40.

CPU RAM and ScratchpadEdit

The TI minicomputer-inspired architecture of the TMS9900 series means that the "Workspace" of registers currently in use are stored in main memory. Because static RAM was also very expensive in the early 80s, TI only gave the machines 256 bytes of fast "scratch pad" RAM where register workspaces could be stored.

The original design for the intended CPU had this 256 bytes internal to the CPU itself, but the 9900 requires registers to be in external memory. Placing this small amount of memory on the 16-bit bus nevertheless helps the performance of the machine (as compared to having registers in 8-bit RAM with a 4-cycle penalty for every access). Some programs, such as Parsec, copied short loops of code to this memory to take advantage of the performance.

The sidecar and PE box expansion systems makes possible an official 32kB RAM expansion.[8] This is not available to all uses – for example an Extended Basic program was restricted to using 24kB with the remaining 8kB available for machine code routines.

Third parties provided replacement memory cards for the PEB. For example, Myarc produced 192kB and 512kB cards.[9] The memory provided by the Myarc cards can be partitioned for use as regular CPU RAM, a RAM disk and a printer buffer.

The Mini Memory plug-in module also contains 4kB of RAM that can be used as a persistent RAM disk (it contained a button cell) or to load a machine-code program.[10]

It is also possible to add an 8kB "supercart" or 32kB "superspace" cartridge via the cartridge slot, which also included the Editor/Assembler GROM. This uses the cartridge ROM space.


Texas Instruments engineers afforded 16kB of Video Display Processor (VDP) RAM to the TI99/4A's graphics coprocessor, a TMS9918A. The VDP RAM was DRAM, with the VDP handling refresh. This is expandable to 192kB with the use of a Yamaha V9938 as a user-designed modification (not a standard upgrade option).

VDP RAM is also used for storing buffers for disk I/O, and variables and code for users' BASIC programs. Hence, the largest BASIC program possible is less than 16kB. BASIC is implemented on the TI-99 series using a second interpreted language called Graphics Programming Language (GPL). The GPL interpreter resides in the ROMs and takes control of the machine at power-up, and was very close to the native 9900 machine code, adding instructions to transparently access the different types of memory in the machine and perform higher level functions such as memory copy and formatted display. Users who install memory expansion still need to upgrade to the Extended BASIC cartridge to use it instead of VDP RAM.

The same VDP is used in the MSX and ColecoVision machines. Further upgrade chips, the 9938 and 9958, were produced by Yamaha based on TI's design. Boards were created that took advantage of these new chips to upgrade the graphics capabilities of the TI-99/4A. The 9938, the more common of the two upgrades, allow 512 × 424 pixels at 16 colours, or 256 × 424 at 256 colours. These upgrades are not a simple drop-in and replace; a small board including the replacement VDP and replacement VDP RAM (usually 128kB) is required. In addition, although the chips were largely software-compatible, certain bugs in the ROMs cause compatibility issues with the new chips. One board, the Mechatronic 80-column card featuring the 9938 require that the user press a button when entering TI BASIC.

Graphics Read-Only MemoryEdit

Graphics Read-Only Memory is another set of memory accessed a single byte at a time through a dedicated memory port, and were auto-incrementing read-only devices. (There is also support in the console for 'GRAM', simulators for which were created by third parties later.) The vast majority of TI cartridges (Disk Manager 2, Editor/Assembler, TI Writer, most games) use this system, as does the console's TI-BASIC. Swapping the TI-BASIC GROM with a GROM removed from a favorite cartridge is a popular modification, as is installing several GROMs into one cartridge allowing a "multicart", with all included GROMs being available in the boot menu.

Since the standard machine does not allow third party machine language support, programmers found their markets decidedly limited to those users who actually added more RAM to their systems. This limitation was alleviated as the price of 32 kB expansion card and a 4 kB "Mini Memory" module eventually came down, but by then the market had moved over to other computers.

Some sophisticated cartridges (for example Parsec, Alpiner, TI LOGO, TI Extended BASIC) include memory-addressable ROM which was available for machine code, primarily for games or applications which demand the speed of machine code. None of this memory is available to the user. In general, ROM-equipped cartridges may be identified by having 28-pin ICs on the board, while the GROM ICs have 14 pins. A small number of cartridges also include a small amount of RAM (notably those games produced for the Milton Bradley MBX expansion system).

Tigervision developed a unique solution to the memory limitation of the standard cartridge slot; a 24kB 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. Tigervision cartridges using the expansion port include Espial and Miner 2049er. A third cartridge, Sprinter, is listed in its 1984 catalog but was not released. Exceltec also released two similar side cartridges, Arcturus[11] and Killer Caterpillar.

Because of the speed bottlenecks (16-to-8-bit bus multiplexer) and the doubly interpreted BASIC, the TI-99 series gained a reputation for being quirky and eccentric, which endeared it to some and maddened others. Many people who had only experienced TI BASIC also considered it very slow, although assembly programs actually manage fairly good speed despite the hardware issues to overcome.


Developers created about 100 99/4A games, most published by Texas Instruments.[12] Some of the most popular were Parsec, TI Invaders, Munch Man, Alpiner, Tombstone City: 21st Century, Hunt The Wumpus, The Attack and Car Wars.

Many TI-developed video games may be forced into cheat mode by holding the shift key and pressing 838. In Alpiner, the player can select which mountain to climb. 838 (with or without SHIFT) in Star Trek gives a random but high level of torpedoes, shields, and warp-drive energy.

InfoWorld criticized the computer's game library as mediocre.[12] TI not only discouraged third-party development for the 99/4A, including games, it also failed to license popular arcade games like Zaxxon or Frogger.[13][14]



The original TI-99/4, released in 1979.

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; the 99/4's (according to Walden C. "Wally" Rhines) "ultracheap keyboard", RF modulator, and ROM cartridges came from the console design. Others within the company persuaded the Lubbock group to use TI's TMS9900 CPU.[5]


Although TI was much larger than any other personal-computer company when it entered the market in 1979, the $1,150 TI-99/4 was, The New York Times in 1983 stated, "an embarrassing failure".[13] David H. Ahl stated that it was "vastly overpriced, particularly considering its strange keyboard, non-standard Basic, and lack of software".[14] 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 more 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.[15] 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 installed base more than twice as large.[16]

99/4A price warEdit

The updated TI-99/4A, released in 1981.

Two years after the 99/4's debut, TI released the 99/4A, very similar, but with a better keyboard and more expansion options.[14] By lowering its price and offering rebates TI sold many more computers;[13] it has been estimated that it had about 35% of the home computer market at its peak[citation needed].

In 1982 TI began a price war with Commodore International by lowering 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, but the company continued to lose shelf space, as Commodore matched the $200 retail price by December 1982.[13][14]

The president of Spectravideo later said that "TI got suckered by" Jack Tramiel, head of Commodore.[14] 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. Although TI and Commodore each owned their own IC fabrication facilities, Commodore created custom ICs to reduce the cost of its computers, while TI continued to use off-the-shelf components and make only relatively small revisions to their motherboards. Commodore also made other cost-cutting changes, including using aluminized cardboard to build RF shields for some of their systems.[17] The TMS9900 required expensive custom semiconductor packaging;[5] TI continued to use high-quality components and materials with the unfulfilled hope that the marketplace would recognize it.

By mid-1982 Jerry Pournelle wrote that TI was "practically giving away the TI-99/4A".[18] An industry joke stated that the company was losing money on each computer, but was making up for it in volume.[14] The 99/4A's list price was $400 that autumn,[13] but the street price including $100 rebate was about $200. Sales peaked at 30,000 a week in January 1983, but on 10 January 1983 Commodore lowered the price of its computers; the VIC-20's wholesale price was $130. In February TI responded by lowering the 99/4A's retail price to $150. In April Commodore again lowered prices, and the VIC-20's bundled retail price reached $100. TI also lowered prices and offered rebates, reducing the 99/4A's retail price to under $100; by this time the company was likely losing money on each computer. In early 1983 TI stopped sales for a month to correct a defect, but—predicting in April that the home-computer market that year would be much larger than most industry analysts expected—continued production at an annual rate of three million, increasing inventory. In May it began offering the PEB for free with the purchase of three peripherals; by this time TI was using price cuts as the 99/4A's primary marketing. 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%.[13][14][19]


The Times stated in June 1983 that Cosby's $100 refund "joke is no longer funny", and that "future options are slim" for TI; Banking firm L.F. Rothschild estimated that the company would only sell two million computers. The low price probably hurt the 99/4A's reputation; "When they went to $99, people started asking 'What's wrong with it?'", one retail executive said.[13]

After losing $111 million after taxes in the third calendar quarter of 1983, TI announced in October 1983 that it was discontinuing the 99/4A, while continuing to sell the TI Professional MS-DOS-compatible computer.[19] (TI stock rose by 25% after the announcement, because the company's other businesses were strong.)[20] With another TI price cut, retailers sold remaining inventory of the former $1,150 computer during Christmas for $49;[14][21] Child World's 90 stores almost immediately sold more than 40,000 computers at the price,[22] and a riot almost broke out at a Greensboro, North Carolina Kmart as shoppers fought over the computer.[23] Discontinued during the video game crash of 1983, 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. A total of 2.8 million units were shipped before the TI-99/4A was discontinued in March 1984.[citation needed]

Lack of third-party developmentEdit

The TI-99/4A is more sophisticated than the VIC-20, offering more memory and more advanced graphics capabilities. However, a number of elements of its design attracted criticism. Peripherals plug directly into the right-hand side of the unit, unless the user purchased the expensive and heavy Peripheral Expansion Box. This design choice causes the computer to not fit well on top of a desk if the user adds more peripherals besides a tape drive and a printer. In addition, the 48-key keyboard layout does not match that of a typewriter very closely. Finally, there was no option for an 80-column display at the time of its introduction. The keyboard and display limitations made it unpopular for word processing.

TI could not make a profit on the TI-99/4A at a price of $99,[24] 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,[13] TI kept strict control over development for the machine, discouraging hobbyists and third-party developers.[18] 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".[14] 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".[25] Its peripherals cost about twice as much as for other computers.[24][13] 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.[3]

Green said that although his company Instant Software had published "hundreds of programs for the TRS-80 [and] want to translate as many as possible for use on the TI-99/4", it could not find anyone among more than 1,000 developers in its network who could port software to the computer, adding "We understand the problems with the system and the efforts Texas Instruments made to make translation difficult".[25] Rival companies were much more open with information. The next issue of Kilobaud Microcomputing reported that a Commodore executive promised that the forthcoming VIC-20 would have "enough additional documentation to enable an experienced programmer/hobbyist to get inside and let his imagination work".[26][27] IBM released complete software and hardware technical information for the Personal Computer when announcing it in 1981,[18] stating that "the definition of a personal computer is third-party hardware and software".[28]

Pournelle in 1982 wrote that because "well over half the really good stuff for microcomputers has come from hobbyists and hackers ... which TI had wrongly concluded that they were ... unimportant", it "found itself cut off from the mainstream". He believed that TI recognized its mistake and would change.[18][29] The company, however, insisted on itself selling others' software, which many developers refused to agree to.[13] 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 TI-licensed circuitry 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".[24] Pournelle wrote after the announcement that "TI once again tells the hobbyists to drop dead".[29]

No official technical documentation from TI was released until the "Editor/Assembler" assembly language development suite was released in 1981, and no system schematics were ever released to the public until after TI had discontinued the computer. In addition, the TI-99/4A's awkward architecture and nonstandard CPU (as opposed to the 6502 and Z80 which all programmers of the day were familiar with) made it difficult to develop for.

Cult followingEdit

The TI-99/4A maintained a cult following for years after its death in the marketplace, in part because of its eccentricities, and in part because TI had actively supported a network of user groups during the production of the machine. It eventually came to achieve a cult following among retro-computer hobbyists. In 2004 a Universal Serial Bus (USB) card and Advanced Technology Attachment controller for IDE hard disks for the PEB were released, and there is still an annual Chicago TI Fair[30] where people congregate to celebrate the historic TI-99 family of computers. Third-party devices such as expanded memory cards, improved floppy controllers, and hardware ramdisks are very stable and popular additions to the machine, although there are no current known sources for these devices. In the early 1980s, a bulletin board system (TIBBS), developed by Ralph Fowler of Marietta, Georgia, running on the 99/4A became very popular and brought many users together. Also, a number of emulators for the TI-99 exist today for PC-based systems.

In 1987, the "Turbo XT" was introduced by Triton. Though rare, it allowed a TI-99/4A and an IBM PC XT to share the same desktop space, though without sharing such things as memory or disk drives.[31] The Turbo XT had at least two serious failings — first, it extended the use of the TI's already marginal keyboard to the XT whereas the reverse would have probably been far more marketable; second, it did not allow the TI to share or use resources with the XT (custom BIOS might have allowed the XT to serve as ramdisk, diskette controller/drives and serial ports).

Successors and clonesEdit

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 therefore have been substantially faster than the original TI-99/4A, and both were to use TI's "HexBUS" serial interface (which was available as an option on the TI-99/4A and could be viewed as a prototype for today's ubiquitous USB — the link for the TI-99/8 includes some images of HexBUS peripherals).

  • TI-99/2,[32] 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).[33] Home-computer prices declined so quickly, however, that by mid-1983 the 99/4A sold for $99.[34][13] The company canceled the 99/2 in April 1983,[19] but planned to exhibit it at the June CES until other companies' press conferences there indicated that competition would increase.[24]
  • TI-99/8 and 99/6[35][24] The 99/8 reportedly had a $200 wholesale price.[14] Privately shown to dealers but not announced at June CES, and formally canceled in October 1983. With 64 kB of RAM[19] expandable to 15 megabytes, larger keyboard, built-in speech synthesis, built-in Pascal operating environment with UCSD Pascal and the full 16-bit data bus available on the expansion port. Designed by Texas Instruments, but abandoned in the prototype stage. Some prototypes are known to exist. In addition, the emulator MESS is capable of running what are believed to be the system's ROMs.
  • Myarc Geneve 9640, an enhanced TI-99/4A clone which was built by Myarc as a card to fit into the TI Peripheral Expansion System[36] and used an IBM PC/XT detached keyboard. Released in 1987, it was in many ways similar to the earlier TI-99/8 which was in prototype form in early 1983. It included a faster processor (12 MHz TMS9995), enhanced graphics with 80 column text mode (via 9938), 16-bit wide RAM, MDOS, and was compatible with nearly all TI software and slot-mounted hardware (an adapter was available to allow the sidecar-only Speech Synthesizer to be installed inside the PEB). A toggle switch was mounted to the side of the PEB to allow insertion of wait states to bring the computer down to the same speed as the original console, allowing compatibility for games and other timing-critical software.
  • SGCPU,[37] the Second Generation CPU card was released by the System 99 User Group in 1996 as a card to be installed in the PEB. It was also known as the TI99/4P, and included standard 9900 CPU, ROMs, and up to 1 MiB of 16-bit RAM using the 'AMS' memory expansion scheme. This card required the HSGPL card, which provided the GROM emulation needed to run the system, and the EVPC, which included the 9938 video processor for display.

  • The Tomy Tutor and its sibling systems were Japanese computers very similar in architecture and firmware to the 99/8. Unlike the 99/8, it was released commercially, but sold very poorly outside Japan. Portions of the operating system and BASIC code are similar to the 99/8. According to Barry Boone (a well known programmer for the TI-99/4A), the Tutor's built-in BASIC uses the same internal one byte tokens as does TI's Extended BASIC, and many of the memory scratchpad locations are placed at the same relative locations as the TI-99/4A and TI-99/8. For instance, keyscan values are returned at offset >75 and floating point is stored at >4A.
  • The Phoenix G2,[38] designed in 2010 by Gary Smith, a member of TI-User Group UK. This machine uses two FPGAs to emulate the entire architecture of the Myarc Geneve 9640 and the TMS9995 microprocessor, thus eliminating reliance on obsolete silicon devices. It incorporates the latest advances in technology, such as SD card readers, ethernet, full VGA output, and now 64 MB RAM.

Technical specificationsEdit

  • CPU: TI TMS9900, 3.0 MHz, 16-bit, 64-pin DIP.
  • Memory: 16 kB VDP RAM (Video Display Processor RAM), plus 256 bytes CPU fast "scratchpad RAM" intended for the TMS9900 processor to maintain register "workspaces".
  • Video: TI TMS9918A VDP (TMS9918 in the earlier 99/4, TMS9929/9929A in PAL versions, 40 pin DIP. Distinct in being the only chip on the TI motherboard with a heat sink on all models. Early models also have a heat sink on the clock generator, the TMS9904.)
    • 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 coincidence (collision detection), and the console supports automatic movement via an interrupt routine in the ROM. There can be no more than 4 visible sprites per horizontal scanline.
    • 16 fixed colors (15 visible, one color reserved for 'transparent' which shows the background color). Transparent is intended for the 9918's genlock functionality used in conjunction with TI's Video Controller Card. This feature was demonstrated in October 1999 at an international TI meeting near Stuttgart, Germany. (This requires a hardware modification to the console itself, as the video input line is not routed on the motherboard.)
    • 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). Bitmap mode can be arranged in such a way as to use less memory but still provide improved color or improved pattern layout, leading to the popularity of so-called "half-bitmap" modes. In fact these modes are not undocumented modes of the VDP (which fully documented this masking) but simply clever layout of Bitmap mode.
    • 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.
  • Sound: TI TMS9919, later SN94624, identical to the SN76489 used in many other systems.
    • 3 voices, 1 noise (white or periodic).
    • Voices generate square waves from 110 Hz to approximately 115 kHz.
    • Console ROM includes interrupt-driven music list playback.

Contemporary useEdit

Texas Instruments TI-99/4A computer. On display at the Musée Bolo, EPFL, Lausanne.

The TI-99/4A enjoys an active after-life in the vintage computing enthusiasts world. There are currently three very active mailing lists where TI-99/4A owners correspond with each other, from matters concerning hardware setup and interfacing equipment to the machine, to advanced software techniques.

  • TI-99/4A Programming Forum (AtariAge)[39] – an active forum, with hardware and software projects on TI-99/4A.
  • TI-99/4A Online User Group (OLUG)[40] – a mailing list, with general chat on all things TI.
  • TI-99/4A and Compatibles Discussion Group[41] – a more technically oriented mailing list, where people will often post technical questions or software routines to try out.
  • SWPB Assembly Programmers Mailing List[42] – the SWPB list is a mailing list dedicated to discussing machine code/assembly language programming on the TMS9900 CPU (SWPB is an assembly instruction, meaning "swap bytes" in TMS9900 Assembly Language).

Modern hardware developmentsEdit

There has been a resurgence in new hardware projects in recent years. Recently, a range of plug in cartridge boards have been developed, allowing enthusiasts to distribute their software projects on cartridge for the first time in many years.[43][44] Additionally, an audio card has been developed featuring the SID chip found in Commodore 64 computers, with a SID player/tracker software application in active development.[citation needed]

Even more recently, a prototype Linux system on a plug-in cartridge has been demonstrated at the 2010 Chicago Faire in America, although the intended feature set has not yet been announced.[45]

A new 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 enhanced features such as removing the 4 sprites on a scan line restriction of the original 9918.[46]

See alsoEdit


  1. ^
  2. ^ "TI‐99/4A user‐dismantled PEB", 99er.
  3. ^ a b Mace, Scott (1984-04-09). "Atarisoft vs. Commodore". InfoWorld. p. 50. Retrieved 4 February 2015.
  4. ^ Texas Instruments TI-99/4, First 16-bit Home Computer,, retrieved 23 September 2014.
  5. ^ a b c Rhines, Walden C. (2017-06-22). "The Texas Instruments 99/4: World's First 16-Bit Home Computer". IEEE Spectrum. Retrieved 2017-07-08.
  6. ^ "Double‐sided, double‐density hex bus 5.25" floppy drive controller", Peripherals, Ninerpedia.
  7. ^ "Compact computer", TI‐99/4A home computer, Hex bus.
  8. ^ Getting Started with the TI-99/4A, 1983
  9. ^ "Myarc 512k ram card", TI*MES (User group magazine), 14 August 1986
  10. ^ Getting Started with the TI-99/4A, 1983
  11. ^ "Cartridge pictures", TI‐99/4A home computer, Hex bus.
  12. ^ a b Mace, Scott (1984-05-07). "In Praise of Classics". InfoWorld. p. 56. Retrieved 6 February 2015.
  13. ^ a b c d e f g h i j k Pollack, Andrew (1983-06-19). "The Coming Crisis in Home Computers". The New York Times. Retrieved 19 January 2015.
  14. ^ a b c d e f g h i j Ahl, David H. (March 1984). "Texas Instruments". Creative Computing. pp. 30–32. Retrieved 6 February 2015.
  15. ^ Osborne, Adam (1980-07-07). "Radio Shack's Videotex". InfoWorld. pp. 9, 28. Retrieved 15 February 2016.
  16. ^ Hogan, Thom (1981-09-14). "State of Microcomputing / Some Horses Running Neck and Neck". pp. 10–12. Retrieved 2019-04-08.
  17. ^ "More Commodore Overheating", Compute!, Atari magazines (59).
  18. ^ a b c d Pournelle, Jerry (July 1982). "Computers for Humanity". BYTE. p. 392. Retrieved 19 October 2013.
  19. ^ a b c d Mace, Scott (1983-11-21). "TI retires from home-computer market". InfoWorld. pp. 22, 27. Retrieved 2011-02-25.
  20. ^ "IBM's Peanut Begins New Computer Phase". Boston Globe. Associated Press. 1983-11-01. p. 1.
  21. ^ Kleinfield, N. R. (1984-12-22). "Trading Up in Computer Gifts". The New York Times. Retrieved 5 February 2015.
  22. ^ Rosenberg, Ronald (1983-12-08). "Home Computer? Maybe Next Year". The Boston Globe.
  23. ^ "Under 1983 Christmas Tree, Expect the Home Computer". The New York Times. 1983-12-10. ISSN 0362-4331. Retrieved 2017-07-02.
  24. ^ a b c d e Mitchell, Peter W. (1983-09-06). "A summer-CES report". Boston Phoenix. p. 4. Retrieved 10 January 2015.
  25. ^ a b Green, Wayne (August 1980). "Publisher's Remarks". Kilobaud. p. 8. Retrieved 23 June 2014.
  26. ^ "Commodore: New Products, New Philosophies". Kilobaud. September 1980. pp. 26–28. Retrieved 23 June 2014.
  27. ^ Thornburg, David D. (April 1981). "The Commodore VIC-20: A First Look". Compute!. p. 26.
  28. ^ Bunnell, David (April–May 1982). "Boca Diary". PC Magazine. p. 22. Retrieved 21 October 2013.
  29. ^ a b Pournelle, Jerry (July 1983). "Interstellar Drives, Osborne Accessories, DEDICATE/32, and Death Valley". BYTE. p. 323. Retrieved 28 August 2016.
  30. ^ "Faire", TI‐99, Main byte.
  31. ^ "Triton turbo", TI‐99 (pictures), Main byte.
  32. ^ "99/2", 99er.
  33. ^ Littlejohn, Harry; Jander, Mark (June 1983). "Texas Instruments' 99/2 Basic Computer". BYTE. p. 128. Retrieved 19 October 2013.
  34. ^ Lock, Robert (June 1983). "Editor's Notes". Compute!. p. 6. Retrieved 30 October 2013.
  35. ^ "99/8", 99er.
  36. ^ OldComputers (online museum).
  37. ^ SGCPU (JPEG) (picture), Info ave.
  38. ^ "G2", TI‐99 UG, UK, archived from the original on 2010-09-19
  39. ^ "TI‐99/4A programming", Atari age (forum).
  40. ^ "TI‐99/4A", Groups (mailing list), Yahoo!.
  41. ^ "TI‐99/4A", Tech groups (mailing list), Yahoo!.
  42. ^ "SWPB", Groups (mailing list), Yahoo!.
  43. ^ "Hardware projects", TI‐99/4A home computer, Hex bus.
  44. ^ You Tube, Google.
  45. ^ "TI GNU/Linux", Projects, Harmless lion.
  46. ^ "Archives", Code hack create.

External linksEdit

  • Ninerpedia – a wiki devoted to the TI-99 series home computers.
  • Hexbus – website with many 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 – a site with everything you wanted to know on the TI-99/4A's predecessor, the TI-99/4.
  • The TI-99/4A Home Computer Page – A site dedicated to the classic 1980's home computer, the TI-99/4A. Forum, links, downloads, and more.
  • Mainbyte, TI‐99 – another good site with 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 – A large repository of gaming and edutainment software for the TI 99/4A.