The TI-99/4 and TI-99/4A are home computers released by Texas Instruments (TI) in 1979 and 1981, respectively. Based on TI's own TMS9900 microprocessor originally used in minicomputers, the TI-99/4 was the first 16-bit home computer. The associated TMS9918 video display controller provides color graphics and sprite support which were only comparable with those of the Atari 400 and 800 released a month later. The TI-99 series also initially competed with the Apple II and TRS-80."Death of a Computer," April 1984, Texas Monthly, retrieved September 20, 2023
The calculator-style keyboard of the TI-99/4 and the high price were cited as weak points. TI's reliance on ROM cartridges and their practice of limiting developer information to select third parties resulted in a lack of software. The TI-99/4A was released in June 1981 with a simplified internal design, full-travel keyboard, and improved graphics. At half the price of the original model, sales picked up significantly and TI supported the 4A with peripherals, including a speech synthesizer and a "Peripheral Expansion System" box to contain hardware add-ons. TI released developer information and tools, but the insistence on remaining sole publisher continued to starve the platform of software. Architectural quirks of both models reduced the performance benefits of the 16-bit CPU.
The 1981 US launch of the TI-99/4A followed Commodore's VIC-20 by several months. Commodore CEO Jack Tramiel began a price war by repeatedly lowering the price of the VIC-20. In late 1982, TI was shipping 5,000 computers a day from their factory in Lubbock, Texas. By 1983, the 99/4A was selling at a loss for under . Even with the increased user base created by the heavy discounts, TI lost US$330 million in the third quarter of 1983 and announced the discontinuation of the TI-99/4A in October 1983. Production ended in March 1984.
The TI-99/4 was intended to fit in the middle of a planned range of TI-99 computers, none of which were released, but prototypes and documentation have been found after the TI-99/4A was discontinued.
Features
Developed by Texas Instruments (TI), the TI-99/4A is a self-contained console with the motherboard, ROM cartridge slot, and full-travel keyboard in the same case. The power supply is external. An RF modulator allows the use of a television as a monitor. Lowercase letters are displayed as small caps, rather than separate glyphs. TI BASIC, an ANSI-compliant BASIC interpreter based on Dartmouth BASIC, is built in and includes support for graphics, sound, and file system access. Later versions of the 99/4A, identified by (C)1983 TEXAS INSTRUMENTS V2.2 on the title page, prevent the use of unlicensed ROM cartridges from third-party manufacturers such as Atarisoft.
Both TI-99/4 models use the 16-bit TMS9900 CPU running at 3 MHz. The TMS9900 is a single-chip implementation of a TI-990 minicomputer. Although a full 16-bit processor, only the 8 KB system ROM and 256 bytes of scratchpad RAM are available on the 16-bit bus.
Peripherals include a 5¼″ floppy disk drive and controller, an RS-232 card with 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.
Video Display Processor Graphics in the 99/4A are generated by an TMS9918A NTSC Video Display Processor (VDP), with a variant for PAL territories. The VDP was developed by TI 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; 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 four can be displayed per scan line. Each sprite is either 8×8 or 16×16 pixels and can be scaled 2× to 16×16 or 32×32.
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, although the CPU does not have direct access to it, and requests reads and writes from the VDP as an intermediary. It is used for storing disk I/O buffers and TI BASIC user programs.
Expansion TI-99 peripherals contain device drivers in ROMs in the hardware. When a new peripheral is attached, it is immediately available for any software that 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 Peripheral Expansion System can hold two RS-232 cards, for a total of four RS-232 ports and two parallel printer ports.
The computer supports two cassette drives through a dedicated port, using a custom data format. 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—the same as 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 24 KB with the remaining 8 KB available for machine code routines. The Mini Memory plug-in module contains 4 KB 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 and allows 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.
Official cards from TI that were released and can be placed inside the PEB include 32 KB RAM expansion card RS-232 and parallel port card P-code card, implementing the UCSD p-system IV.0 by acting as a ROM-disk Diskette drive control card. The design allows controlling both drives internally in the PEB and external drives.
Peripherals designed to be used without the PEB also exist.
Speech synthesizer
In the late 1970s and early 1980s, TI was a pioneer in speech synthesis because of its 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. Alpiners 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.
History In the late 1970s, TI was a successful manufacturer of large computers and the largest semiconductor manufacturer in the world. In 1977, groups within TI 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 were both working at TI's consumer products division in Lubbock, Texas, and continually competed. According to Wally Rhines, the 99/4's "ultracheap keyboard" (with calculator-style keys), RF modulator, and ROM cartridges came from the console design. The Lubbock teams were merged and directed towards the home computer market.
Others within the company persuaded the Lubbock group to use TI's TMS9900 CPU. This was in keeping with TI's "one company, one computer architecture" concept, where a single processor model would scale from consoles to its high-end minicomputers. The TMS9900 is a single-chip implementation of TI's 16-bit TI-990 minicomputer, and is the CPU in low-end models of that platform. Feature-limited single-chip versions of popular minicomputer designs from the 1960s were popular in the mid-1970s and newly designed 16-bit and 32-bit CPUs like the Intel 8086 and Motorola 68000, respectively, quickly rendered these earlier designs obsolete. Many of the TMS9900's quirky features, like processor registers in main memory, came from its minicomputer roots where such concepts were more common.
The team working on the high-end personal computer was merged into TI's Data Systems Division, which had the TI 990 and various computer terminals; the division ended the personal computer because it was a threat to the minicomputer. TI's European headquarters worked on another home computer, where a third party consulting firm was contracted to produce a prototype codenamed "Mojo". This was based on TI's version of the 8-bit Intel 8080 supported by an all-TI chip set. After a series of discussions, Mojo was abandoned and the Consumer Products concept moved forward.
99/4 TI's catalog included a huge variety of analog and digital integrated circuits already widely used in microcomputers, giving it a single-source advantage no other company could meet. TI used this position to take over markets, as it did in the mid-1970s introducing its first scientific calculators. These underpriced its former customers like Commodore and drove them out of the calculator business. Observers expected TI would do the same to the microcomputer market if it released a competitive system. The New York Times suggested that the entry of TI and Hewlett-Packard would reshape the entire industry.
Through the development period, several companies attempting to enter the home computer market were faced with significant pushback from the Federal Communications Commission (FCC). The FCC had developed new rules for consumer devices that connected directly to televisions in an effort to control ongoing complaints about interference by poorly shielded devices. Televisions of the era generally had only a single antenna input, and thus connecting to them required the internal video signal of the device to be converted to radio frequency using an RF modulator. If these were poorly shielded the signal would leak out and could be picked up in the antennas of nearby televisions.
The new rules were extremely stringent and difficult to meet. TI continued battling the FCC both in the lab and in Congress, where it had considerable power due to its position within Texas's high-tech industry. It failed to meet the FCC requirements as the release date approached. The company eventually gave up and bundled a modified Zenith Electronics television with the computer, as a computer monitor, eliminating the need for the RF modulator by connecting directly to the TV's internal circuitry using a composite video signal. This put the introductory price at .