TI-99/4 and TI-99/4A | 1979 ~ 1981

TI-99/4

 The TI-99/4 and TI-99/4A are home computers released by Texas Instruments in 1979 and 1981, respectively. The TI-99/4 was based on Texas Instruments' TMS9900 microprocessor, which was originally used in minicomputers, making the TI-99/4 the first 16-bit home computer. The related TMS9918 video display controller provided color graphics and sprite support, comparable to the graphics performance of the Atari 400 and 800 at the time. The TI-99 series initially competed with the Apple II and TRS-80.

The calculator-style keyboard of the TI-99/4 was criticized as a weakness, and the reliance on TI's ROM cartridges and limited developer information provided to only a few third parties led to a lack of software. The TI-99/4A, released in 1981, aimed to address these issues by simplifying the internal design, offering a full-travel keyboard, improved graphics, and a unique expansion system. The TI-99/4A was launched at half the price of the original model, leading to a significant increase in sales, and TI released several peripherals to support it, including a speech synthesizer and a "Peripheral Expansion System" box that could accommodate additional hardware. Although TI made developer information and tools available, it still maintained a proprietary publishing policy, failing to resolve the software shortage issue on the platform. Both models had architectural flaws that limited the performance advantages of their 16-bit CPUs.

The TI-99/4A was released a few months after Commodore's VIC-20. Commodore's CEO, Jack Tramiel, initiated a price war by continuously lowering the price of the VIC-20, forcing TI to reduce its prices as well. By the end of 1982, TI was shipping 5,000 computers a day from Lubbock, Texas. However, in 1983, the TI-99/4A was sold for under $100, resulting in losses, and in the third quarter of 1983, TI recorded a loss of $330 million. Ultimately, TI announced the discontinuation of the TI-99/4A in October 1983, with production ceasing in March 1984.

The TI-99/4 was released as a mid-range model in the planned TI-99 computer lineup, but no other models were released afterward. However, some prototypes and documents were discovered after the discontinuation of the TI-99/4A.

The TI-99/4A is a standalone console that houses the mainboard, ROM cartridge slot, and full-travel keyboard in a single case. The power supply is external, and it can use a television as a monitor via an RF modulator. Lowercase letters are displayed in a lowercase form instead of having separate glyphs. TI BASIC is an ANSI-compliant BASIC interpreter based on Dartmouth BASIC, supporting graphics, sound, and file system access. Subsequent versions of the 99/4A have a title page stating (C)1983 TEXAS INSTRUMENTS V2.2, which prevents the use of unofficial ROM cartridges from third-party manufacturers.

Both the TI-99/4 and TI-99/4A models use a 16-bit TMS9900 CPU operating at 3 MHz. The TMS9900 is a single-chip implementation of the TI-990 minicomputer, and while it is a full 16-bit processor, only the system ROM and 256 bytes of scratchpad RAM can access the 16-bit bus.

Peripherals include a 5¼-inch 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 audio coupler, a tape drive using standard audio cassettes as media, and a 32KB memory expansion card.

The graphics of the 99/4A are generated using the TMS9918A video display processor (VDP). This VDP, developed by Texas Instruments, was also used in the ColecoVision and SG-1000 consoles and is included in the MSX computer standard. The TMS9918A supports both character-based and bitmap display modes, as well as hardware sprites. A total of 32 single-color sprites can be used, with a maximum of 4 sprites displayed per scan line. Each sprite can be 8×8 or 16×16 pixels in size and can be scaled from 2x to 16x.

The 99/4A provides 16KB of RAM as VDP RAM. This VDP RAM is the largest writable memory block in the TI-99/4A architecture and is used to store disk I/O buffers and TI BASIC user programs. Access to this memory can only be done through the VDP.

TI-99 peripherals operate through built-in device drivers. When a new peripheral is connected, it becomes immediately available in software, and all device access is handled using a file-based I/O mechanism. This allows new devices to be added without updating the software. The Peripheral Expansion System can accommodate two RS-232 cards, supporting a total of four RS-232 ports and two parallel printer ports.

This computer supports two cassette drives through dedicated ports, using a special data format. In NTSC-based machines, composite video and audio are output through another port and modulated to a television via an external RF modulator. PAL-based machines output a more complex YUV signal, which is also modulated externally to UHF.

Two digital joysticks can be connected through a single DE-9 port. This port is the same as Atari's joystick port, but the pin arrangement is not compatible. Using third-party adapters, Atari-compatible joysticks can be used. TI officially sold a 32KB RAM expansion module. This memory is not used for all purposes; for example, expanded BASIC programs can only use 24KB, with the remaining 8KB reserved for machine language routines. The Mini Memory plug-in module provides 4KB of battery-backed RAM, which can be used as a permanent RAM disk or to load machine language programs.

The TI-99/4A can be upgraded through the Peripheral Expansion Box (PEB) or Peripheral Expansion System, which is an external chassis that accommodates expansion cards. This chassis has its own linear power supply and full-height 5¼-inch floppy disk drive bays. Each card has an LED that blinks when accessed by software. The power supply's card slot section is nonlinear, and each card has an onboard power regulator to meet its specific voltage requirements. This allows for reduced power consumption in partially loaded PEBs and enables the use of special cards with unique voltage requirements.

The PEB supports analog audio input from the expansion bus, allowing the audio from the speech synthesizer to be sent to the console for monitoring. Audio can also be transmitted to the PEB via ribbon cables, opening the possibility of moving the speech synthesizer to the PEB or using audio cards that provide more functionality than the console's built-in sound. No cards were officially released by TI.

Officially released cards for the PEB by TI include a 32KB RAM expansion card, RS-232 and parallel port cards, a P-code card running UCSD P-System IV.0, and disk drive control cards.

There were also peripherals that could be used without the PEB.

In the late 1970s and early 1980s, TI was a pioneer in speech synthesis technology thanks to the Texas Instruments LPC Speech Chips used in the Speak & Spell toy. There were speech synthesizer modules for the TI-99/4 and 4A, which were offered for free with the purchase of some cartridges and were used in video games like Alpiner and Parsec. The speech in Alpiner includes both male and female voices, with a mocking tone when the player makes a wrong move.

This speech synthesizer uses a variant of linear predictive coding (LPC) and has a small built-in vocabulary. The original plan was to release a small cartridge to expand the vocabulary of the speech synthesizer, but this plan was canceled due to the success of software speech synthesis in the Terminal Emulator II cartridge.

In 1977, several teams within Texas Instruments (TI) were designing a home computer to compete against video game consoles, the TRS-80, and the Apple II, as well as a high-end personal computer with a hard drive. The first two teams worked in TI's consumer products division and continuously competed. According to Wally Rhines, the "ultra-low-cost keyboard" (calculator-style keys), RF modulator, and ROM cartridges of the 99/4 stemmed from console design. Eventually, the two teams merged to target the home computer market. Meanwhile, a third team joined TI's data systems division, which dealt with minicomputer products and various computer terminals, and they considered all-in-one machines to be a threat, leading to the project's termination.

Others at TI persuaded the Lubbock group to use TI's TMS9900 CPU. This aligned with TI's concept of "one company, one computer architecture," aiming for a single processor model to extend from consoles to advanced minicomputers. The TMS9900 is a single-chip implementation of TI's 16-bit TI-990 minicomputer design. Limited-function single-chip versions based on popular minicomputer designs from the 1960s gained popularity in the mid-1970s, but newer 16-bit and 32-bit CPUs like the Intel 8088 and Motorola 68000 provided superior performance. The unique features of the TMS9900, such as processor registers being stored in memory, were more common in minicomputers of the time.

Meanwhile, another home computer product was emerging from TI's European headquarters. A third consulting company was prototyping under the code name "Mojo," based on TI's 8-bit Intel 8080 version, fully supporting TI chipsets. After several discussions, Mojo was abandoned, and the home computer concept from the consumer products division continued.

By 1979, TI had already established a successful path as a large computer manufacturer and was the world's largest semiconductor manufacturer. TI was extensively producing microcircuits and digital integrated circuits, providing a competitive edge in the microcomputer field. TI aimed to dominate the market, and in the mid-1970s, it released its first scientific calculator, pushing out previous customers like Commodore and gaining an advantage in the calculator market. It was anticipated that if TI released a competitive system, the microcomputer market would also be reshaped.

During the development period, several companies attempting to enter the home computer market faced strong regulations from the Federal Communications Commission (FCC). The FCC established new regulations to address interference issues with consumer devices connected directly to TVs, and since most televisions at the time had only one antenna input, RF modulators were needed to connect computers, leading to potential signal interference issues.

TI constantly fought with the FCC to resolve these regulatory issues. TI attempted to address the regulatory problems in laboratories and Congress, but as the launch date approached, they could not resolve the issue. Therefore, TI modified Zenith Electronics' televisions to serve as computer monitors, eliminating the RF modulator and connecting directly to the TV using composite video signals. As a result, the initial price of the 99/4 was set at $1,150, equivalent to about $4,253 in 2023.

However, the 99/4 struggled with poor sales. There was little software available, and most developers did not port products to TI's 16-bit CPU. The machine received negative reviews across nearly all reviews at launch. Issues such as the keyboard, lack of lowercase support, limited expandability, and software shortages were highlighted. In July 1980, Adam Osborne noted that the 99/4 was priced at $1,400, more expensive than the popular Apple II at $950, indicating sales difficulties. By the summer of 1981, TI had sold fewer than 20,000 units, significantly less than Apple, RadioShack, or Atari. The 99/4 was described as "incredibly expensive, particularly with its strange keyboard, non-standard BASIC, and software shortages."

After the failure of the 99/4, TI launched the 99/4A model in 1981 to recover. This model offered a typewriter-style keyboard and added more expansion options. Initially priced at $525, the price was continuously lowered. In early 1982, TI reduced the price to $200 and featured Bill Cosby in advertisements. After the price drop, sales of the 99/4A surged, but many issues persisted. TI continued to lower prices, and the 99/4A remained on the market until spring 1983, with many retailers selling stock for as low as $49. TI decided to discontinue the 99/4A in March 1984, with total shipments reaching 2.8 million units. The 99/4A is recorded as one of the first major systems to be discontinued in the home computer market, followed by systems like Coleco Adam, Mattel Aquarius, Timex Sinclair 1000, and IBM PCjr, which faced similar fates.

To build a complete 16-bit system, TI had to redesign many of its existing 8-bit support chips. However, TI decided to use most of the existing devices in the system. As a result, only part of the system was 16-bit, while the rest used a second 8-bit computer bus.

One of the key features of the TMS9900 is the inclusion of multiple sets of processor registers. This design originated from minicomputers, where time-sharing or multitasking operating systems were typically run, or real-time computing was used. In these environments, the ability to switch quickly between programs was advantageous, so the TMS9900 could store multiple sets of 16-bit registers in main memory and quickly switch context by changing a single workspace pointer register.

The new design included 256 bytes of random access memory (RAM) on the 16-bit bus to store up to 8 sets of registers. This RAM area is known as "scratchpad memory." All instructions for the processor are 16-bit, so the 8KB of internal system read-only memory (ROM) is also located on the 16-bit side. In fact, the program counter, status register, and workspace pointer register are implemented on the chip itself.

On the 8-bit side of the system, most of the RAM and nearly all support chips are located, particularly the video display controller (VDP). All access to the VDP system is executed 8 bits at a time. The system's RAM is managed by the VDP, and the CPU can only access memory when the VDP is not using it. This results in user programs and data being read through two machine cycles, effectively halving the speed. According to TI's former microprocessor manager who oversaw the development of the TMS9900, this offsets the performance advantage of the 16-bit processor.

The machine language instructions of the TMS9900 require word alignment, necessitating a minimum of 16 bits for each instruction. At the time, memory was expensive, making the size of this format a concern. Additionally, programming the 8-bit side of the system with 16-bit code was somewhat complex. To address this, TI developed a pseudo-assembly language called "Graphic Programming Language" (GPL). GPL is interpreted by the CPU and dynamically translates GPL instructions into one or more TMS9900 instructions. GPL includes utility routines such as clearing memory blocks. All software initially distributed on ROM cartridges was written using GPL, sometimes referred to as GROM.

At launch, the system included only TI's built-in BASIC interpreter as the sole user-accessible programming language. According to Creative Computing Benchmark, it runs at about half the speed of the Apple II.