Texas Instruments TI-99/4A

The TI-99/4 series uses the 16-bit TMS9900 CPU running at 3 MHz. The TMS9900 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. There are 256 bytes of volatile "scratchpad" memory for storage of workspaces.

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 video chip 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.

Peripheral Expansion Box or PEB

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.[8] 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 known as a pioneer in speech synthesis because of its Speak & Spell line of toys, which used the Texas Instruments LPC Speech Chips. 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 many TI-written video games (including 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. The 99/4's (according to Wally Rhines) "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.[9] The system only supported uppercase characters.

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".[10] David H. Ahl stated that it was "vastly overpriced, particularly considering its strange keyboard, non-standard Basic, and lack of software".[4] 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.[11] 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.[12] The TI-99/4 prototype was known as the Texas Instruments Dimension 4.[13]

Late period, cost-reduced version of the TI-99/4A with beige case

Two years after the 99/4's debut, TI released the 99/4A, very similar, but with a better keyboard and more expansion options.[4] By lowering its price and offering rebates TI sold many more computers.[10] By the end of 1982, the TI-99/4A had about 35% of the American home computer market.[1]

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.[10] By mid-1982 Jerry Pournelle wrote that TI was "practically giving away the TI-99/4A".[14] An industry joke stated that the company was losing money on each computer, but was making up for it in volume.[4] The 99/4A's list price was $400 that autumn,[10] with a street price, including $100 rebate, of $200. Commodore matched the $200 price in December 1982.[4]

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%.[10][4][15]

The president of Spectravideo later said that "TI got suckered by" Jack Tramiel, head of Commodore.[4] 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.[10] 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.

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.[15] (TI stock rose by 25% after the announcement, because the company's other businesses were strong.)[16] With another TI price cut, retailers sold remaining inventory of the former $1,150 computer during Christmas for $49;[4][17] Child World's 90 stores almost immediately sold more than 40,000 computers at the price,[18] and a riot almost broke out at a Greensboro, North Carolina Kmart as shoppers fought over the computer.[19]

A total of 2.8 million units were shipped before the TI-99/4A was discontinued in March 1984.[1][20] 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.

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,[21] 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,[10] TI kept strict control over development for the machine, discouraging hobbyists and third-party developers.[22][14] 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".[4] 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".[23] Its peripherals cost about twice as much as for other computers.[21][10] 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.[5]

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".[23] Rival companies were much more open with information. The next issue of Kilobaud Microcomputing reported that a Commodore executive promised that the VIC-20 would have "enough additional documentation to enable an experienced programmer/hobbyist to get inside and let his imagination work".[24][22] IBM released complete software and hardware technical information for the IBM PC when announcing it in 1981,[14] stating that "the definition of a personal computer is third-party hardware and software".[25]

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 ... were ... unimportant", it "found itself cut off from the mainstream". He believed that TI recognized its mistake and would change.[14][26] The company insisted on publishing others' software, however, which many developers refused to agree to.[10] 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",[21] and Pournelle wrote that "TI once again tells the hobbyists to drop dead".[26]

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.

Texas Instruments TMS9900 @ 3 MHz, 16-bit, 64-pin DIP

• 256 bytes scratchpad RAM for the CPU
• 16 kB Video Display Processor RAM

 TMS9918A VDP, 40 pin DIP. The earlier 99/4 uses the TMS9918. PAL systems use the "9929" versions of each.

• 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.

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 playback

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 both were to use TI's HexBus serial interface.

• TI-99/2,[29] 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).[30] Home-computer prices declined so quickly, however, that by mid-1983 the 99/4A sold for $99.[31][10] The company canceled the 99/2 in April 1983,[15] but planned to exhibit it at the June CES until other companies' press conferences there indicated that competition would increase.[21]
• TI-99/8 and 99/6[32][21] The 99/8 reportedly had a $200 wholesale price.[4] Privately shown to dealers but not announced at June CES, and formally canceled in October 1983. With 64 kB of RAM[15] 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.

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.

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.[33] It uses an IBM PC/XT detached keyboard. Released in 1987, it is similar to the unreleased TI-99/8 system. It includes a faster processor (12 MHz TMS9995), 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 mounted to the side of the PEB allows insertion of wait states to slow the computer to the same speed as the original (for compatibility with games and other timing-critical software).

The Phoenix G2,[34] 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.

The Second Generation CPU card (SGCPU)[35] 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 requires the HSGPL card, which provides the GROM emulation needed to run the system, and the EVPC, which included the 9938 video processor for display.

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[36] 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.

A range of plug in cartridge boards have been developed, allowing software projects to be distributed on cartridge.[37][38] 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.

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 enhanced features such as removing the 4 sprites on a scan line restriction of the original 9918.[39]