Texas Instruments TI-99 / 4A

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Texas Instruments TI-99 / 4A
TI99-IMG 7143.jpg
logo
Manufacturer United StatesUnited States Texas Instruments (TI)
Type Home computers
publication United StatesUnited States May 31, 1981
End of production world October 28, 1983
Factory price United StatesUnited States525 USD (1981) 1490 DM (1981)GermanyGermany
processor 16-bit TMS9900
  • 16-bit data bus
  • 3 MHz clock frequency
  • 64 KB address space
random access memory 16 KB RAM (max. 52 KB)
256 bytes SRAM (16-bit CPU-RAM)
graphic 8-bit TMS9918A (NTSC)
8-bit TMS9928A (SECAM)
8-bit TMS9929A (PAL)
  • Max. 256 × 192 pixels
  • Max. 40 × 24 characters
  • Max. 15 colors
  • Max. 32 sprites
Sound 8-bit TMS9919
  • 3 tone generators
  • 1 noise generator
Disk Plug-in modules (max. 30 KB)
Compact cassettes (max. C60)
5¼ inch diskettes (max. 89 KB)
operating system TI-BASIC interpreter (primary)
GPL interpreter (secondary)
predecessor TI-99/4 (1979)
successor TI-99/2 (no series production)
TI-99/8 (no series production)
Geneve 9640 (1987)

When Texas Instruments TI-99 / 4A (short TI-99 / 4A , commonly known as "Neunundneunziger" ) is, to a home computer of the US technology group and at the beginning of the 1980s the world's leading semiconductor manufacturer Texas Instruments (TI). The computer has a 16-bit main processor , which was very powerful for the time , 16  kilobytes of working memory (RAM), 26 kilobytes of permanent memory (ROM) as well as special components for image and sound output. It was first presented to the world at the Summer Consumer Electronics Show held in Chicago from May 31 to June 3, 1981 .

Like most contemporary home and small computer has also the TI-99 / 4A via an interpreter , with the aid of the computer in a proprietary dialect of the programming language BASIC operated and can be programmed. Compared to its predecessor model TI-99/4 - the first series-produced 16-bit home computer - the color and fuel-capable TI-99 / 4A is characterized above all by improved graphics capabilities, a more comfortable keyboard and a lower price. The computer, which was advertised intensively with these features, was available for USD 525 when it was launched in North America in 1981 and  shortly afterwards for DM 1,490 in West Germany.

At the end of 1982 the TI-99 / 4A temporarily achieved market leadership in its device class. However, increasing competition from manufacturers such as Commodore , Atari and Sinclair , a failed marketing strategy and above-average production costs led to steadily growing financial losses for the manufacturer as early as the summer of 1982. As a result, TI announced on October 28, 1983 its withdrawal from the home computer market and ceased production of the TI-99 / 4A. A total of around 2.8 to 3 million devices were sold worldwide. This makes the TI-99 / 4A the first 16-bit computer to be widely used among private users. The special relevance of the TI-99 / 4A in terms of technology history is derived from this fact.

history

Weaknesses of the previous model TI-99/4

TI-99/4 (1979)

The predecessor model TI-99/4 was made ready for series production at the end of 1979, but could not be delivered in large numbers until the beginning of 1980. In addition, the TI-99/4 was initially not approved for operation with commercially available televisions, as TI was not able to meet the strict requirements of the US Federal Communications Commission (FCC) for radio interference suppression from RF modulators . The computer, which was then only offered as a package with an expensive Zenith color monitor, remained unaffordable for most private users with a package price of initially 1150 USD in North America, which was increased to 1400 USD by autumn 1980, and at 2700 DM in West Germany.

In addition, the TI-99/4 suffered from technical defects. This included in particular the stiff chewing gum keyboard, which does not include all standard characters and is therefore unsuitable for entering large amounts of data . Graphics skills were also limited. For example, the computer cannot display bitmap graphics or lowercase letters, which makes it almost unusable for word processing purposes. Further production delays, a software offer with only 30 titles at the end of 1980, limited BASIC programming options and sometimes disparaging reviews in the specialist press gave the TI-99/4 a rather mediocre image.

Sluggish sales finally led TI to offer the computer individually at a significantly lower price of 600 USD or 1500 DM - without success, the TI-99/4 remained a slow seller. Those responsible at TI then initiated a thorough revision and further development of the previous model to the TI-99 / 4A in the fall of 1980 in order to finally be able to offer a competitive home computer.

Further development of the previous model to the TI-99 / 4A

TI-99 / 4A (1981)

The head of consumer electronics named Peter Bonfield suggested by the revision of the previous model, the replacement of the originating from the Group's own production 16-bit CPU TMS9900 through the purchase of cheaper 11 USD 8-bit CPU Z80 of Zilog . However, managing director Mark Shepperd did not want to use the technically backward microprocessor from a third-party manufacturer . In addition, TI's semiconductor division hoped to make large profits within the group on the sale of the TMS9900, which cost only $ 2.25 to manufacture. In November 1980 Bonfield was replaced by Don Bynum, who took over the technical direction of the revision of the TI-99/4 (code name "Ranger" ) and kept the TMS9900.

The sound chip, I / O module and system bus also remained largely unchanged. In order to reduce the production costs to 340 USD, however, more highly integrated versions of the circuits were used. The expansion port has been modified to expand its functionality. By omitting the pocket calculator function Equation Calculator , the extensive permanent memory has been slimmed down by 5 KB. The main memory has also been reduced by 256 bytes, with the associated possible problems with existing programs being accepted.

The decisive difference to the previous model was the improvements to the TMS9918 graphics chip, which enable the display of lower case letters, bitmap graphics and operation with SECAM and PAL televisions. In contrast to its predecessor, the new model could therefore also be offered on markets outside of North America. The graphics chip built into the US version of the new computer was named "TMS9918A". The attached, for Engl. "Advanced" (German: "further developed") capital letter "A" was added to the model name of the TI-99/4 in the course of the search for a suitable name for the successor model.

There have also been changes to the exterior: The TI-99 / 4A does not have a loudspeaker or microphone connection. The console now had a typewriter keyboard with an additional function key and auto-repeat function. TI also commissioned the development of new peripheral devices. The TI-99 / 4A was finally ready for the market in the summer of 1981 through the verification of the electromagnetic compatibility of the computer and the HF modulator with the FCC.

Marketing and price development

TI Goleta, California branch
TI advertising partner Bill Cosby (1982-83)
Competitive model Commodore VC20 (1981)

In contrast to the case of the globally successful home computers from Commodore and Atari, which are mostly manufactured in the low-wage countries of Southeast Asia , the TI-99 / 4A, which is manufactured in the Texan cities of Lubbock , Abilene and Austin , in Almelo in the Netherlands and Rieti in Italy , remained notable in North America, Great Britain , West Germany, France, Italy and the Netherlands. TI had established sales structures in the United States when it was launched, and the TI-99 / 4A was available in its own stores as well as independent specialty stores, department stores and supermarkets. Alternatively, the computer could be obtained directly from the factory via mail order.

Initial sales success and market leadership

For a TI-99 / 4A, the middlemen had to pay around USD 340 in the summer of 1981, while the actual retail price of USD 550 was initially slightly higher than the recommended retail price of USD 525. Weekly production at this point was just under 8,000 units. Based on optimistic sales forecasts, sales manager William J. Turner had the list price gradually lowered to initially $ 450 and then $ 375 by the end of 1981. The profit margin could be kept at a stable level of 40 percent per computer by reducing production costs.

In February 1982 TI had to temporarily take the TI-99 / 4A off the market due to defective power supplies. The group suffered financial losses of USD 50 million as a result. To overcome this crisis, that is, to boost sales, Turner decided to market it more aggressively and then lowered the price to USD 300, accompanied by an advertising campaign with the slogan “TI's Home Computer. This is the one ” , for which the well-known comedian Bill Cosby was hired and rewarded with USD 1 million per year. At the behest of Turner, who was promoted to director of the entertainment electronics department in August 1982, TI entered into an open price war with its main competitor Commodore and its home computer VC20 . Turner was rightly hoping for large orders from the most important retail chains such as JC Penney , Sears Roebuck , K-Mart and Toys “R” Us . Discounts of $ 100 reduced the effective retail price to below $ 200 on September 1, 1982, fueling rumors that TI was holding stocks of up to 50,000 unsold units. TI advertising partner Cosby joked with the public at these discounts for the TI-99 / 4A about how easy it is to sell a home computer if you give customers a reward of $ 100 for it.

Turner's aggressive marketing strategy led to a significant increase in demand and expansion of production in the fall of 1982. For every VC20 sold, there were three copies of the technically superior TI-99 / 4A. Monthly production between July and December 1982 was around 150,000 units, while the sales network now comprised 12,000 sales outlets. At peak times, up to 5,000 units were being produced per day. A further reduction in production costs did not succeed, however, and profits per computer sold fell by 50 percent. The entertainment electronics division's sales grew to $ 200 million, a ten-fold increase in a short period of time. A total of around 500,000 copies were sold in 1982. With 575,000 users and a market share of around 35 percent, the TI-99 / 4A was considered the most widely used home computer in the United States at the turn of the year 1982/83.

In the following year, demand remained initially high. Around 30,000 units a week were sold in January 1983 alone. Orders from dealers also remained at a high level. In April 1983 the number of units sold reached the million mark. In Europe, however, this success could not be continued; In West Germany, TI managed to gain a market share of only 8 percent by the end of 1983. Wolfgang Glöckle from the German TI branch then stated in an interview that the group had now "made the breakthrough for home computers in Germany as well."

Sales crisis and cessation of production

TI-99 / 4A "QI" (1983)
Side view (left)
Side view (right)
Rear view

With the Commodore 64 (C64) and Sinclair ZX Spectrum in particular, the TI-99 / 4A faced new competition from summer 1982. TI then considered developing an improved TI-99 / 4A with 64 KB of RAM and CP / M capability, in order to catch up with the more powerful C64 in particular. However, after chief developer Bynum resigned in April 1983, these plans were dropped. With a view to the VC20, which now only costs 99 USD, TI also lowered the price for the TI-99 / 4A in June 1983 to 150 USD and 550 DM. This meant that the sales price was only 25 USD above the manufacturing cost of 125 USD.

Meanwhile, production continued to run at full speed. Turner's sales forecasts turned out to be illusory. From April 1983 onwards, increasing numbers of items were sent back from the US sales offices to the corporate headquarters, as they had turned out to be unsaleable. Turner was then relieved of his post and replaced in May by J. Fred Bucy, who ended the collaboration with Cosby and initiated a new advertising campaign with a stronger focus on the education market. For the West German market, for example, the slogan “You learn by playing” was used. Jerry Junkins was put in charge of sales, who immediately closed several production facilities, ordered a new overhaul of the electronics and reduced the sales price to USD 99. The dramatic price decline of the TI-99 / 4A spoke Everett Purdy, vice president of supply chain services merchandise, in the prestigious New York Times by a in the computer industry unprecedented "self-destruct pattern" (Engl. "Self-destruct pattern" ) . From the revision, the beige version of the TI-99 / 4A emerged in June 1983 without aluminum cladding and status display. With the computers of the Atari XL series brought onto the market at the same time , the TI-99 / 4A received further serious competition.

By August 1983, the number of integrated circuits had been reduced from 42 to 35. In addition, the computer received a power supply with improved thermal management. In addition, this last model version of the TI-99 / 4A, bearing the unofficial name affix "QI" ( "quality improved" ), was provided with a slightly modified operating system that prevented the plug-in modules from Atarisoft and a few others, which were only equipped with EPROM chips, from failing unpopular third-party provider, and was supposed to boost sales of TI's own program releases. As part of these marketing efforts, the prices for peripheral devices were also reduced by 50 percent. However, these measures did not change the declining attractiveness of the computer - customers increasingly turned to the C64.

TI had already canceled the market launch of the TI-99/2, which was designed for the lower market segment, in July. At Bucy's behest, the development of the TI-99/8 (code name "Armadillo" ), which was intended to be the successor to the TI-99 / 4A, was discontinued when there were rumors in the fall of IBM entering the home computer business and a low-end computer from Apple came up.

As early as the summer of 1983, the consumer electronics division's debt was $ 119 million. By the end of the year, that amount rose to nearly $ 223 million. Since the price war with Commodore threatened to drive the entire group into bankruptcy, the group management announced the withdrawal from the home computer market on October 28, citing the losses, which had been driven up by the lack of reorders and full warehouses. In order to preserve the company's image, customer service was maintained for a long time and the production of new software was announced. Letters from the company management were enclosed with new devices, which contained a reference to the maintenance of the one-year warranty on the part of TI as well as a hotline telephone number ( 800–TI–CARES) via which customer questions related to the discontinuation of production of the TI-99 / 4A were answered.

Inventory sales at bargain prices

Competitive model Commodore 64 (1982)

For the Christmas business of 1983, the price was temporarily reduced to 50 USD, which temporarily reduced the sales success of the C64. In Great Britain, the price fell to £ 100 and thus on the level of the local, technically less powerful and only with rubber keys equipped cheap computer Sinclair ZX Spectrum 16K .

In West Germany the price fell to DM 475 by September 1983. To create additional incentives to buy, TI extended the warranty on new devices from six months to a full year from October. In addition, the computer continued to be advertised. At the beginning of November the TI-99 / 4A only cost 398 DM with a further sharp decline, which prompted Vobis managing director Theo Lieven to comment that “you can't get into computer technology cheaper and better”.

In the last two months of 1983 approximately 150,000 units were sold worldwide. The Texans made a loss of no less than USD 50 per computer sold. In January 1984 the total number of copies sold reached the 2.5 million mark.

At the beginning of 1984, the sell-out of the TI-99 / 4A continued at an undiminished rate. In West Germany, the price plummeted to 150 DM. In the course of the warehouse sales for 298 DM, TI-Germany even sold its no longer needed home computer exhibition stands, including a TI-99 / 4A and a game bundle comprising 17 titles. While the warehouses of TI and various third-party suppliers in the United States still had plenty of peripheral devices, accessories and software, the comparatively small West German market soon experienced supply bottlenecks. This gave rise to the curious case of a supply and price anomaly in German-speaking countries : The high number of customers who still owned the TI-99 / 4A in the course of sales at low prices caused the demand for software and accessories to skyrocket. Since both were hardly available anymore due to the cessation of production in the autumn of 1983, prices for used goods soon exceeded those for new goods.

On March 28, 1984, TI officially ceased sales of any products associated with the TI-99 / 4A. The Triton mail order company from San Francisco took over the remaining stock. The inventory sales, some of which went beyond 1984, brought the total number of units sold close to the three million mark. Around 150,000 devices were used in western Germany, Austria and Switzerland. With these sales figures, the TI-99 / 4A is considered to be the first 16-bit microcomputer to be widely used by private users.

Due to its advanced 16-bit main processor, the TI-99 / 4A was still very popular for a few years, also in West Germany. At the end of 1985 a used, functional TI-99 / 4A cost an average of about 130 DM there.

Development of the recommended retail price for the TI-99 / 4A in the USA and West Germany

country 6/1981 1/1982 4/1982 10/1982 1/1983 2/1983 4/1983 5/1983 9/1983 1/1984
United StatesUnited States $ 525.00 $ 450.00 $ 399.00 $ 299.95 $ 299.95 $ 249.95 $ 225.00 $ 149.95 $ 100.00 $ 49.95
GermanyGermany 1490.00 DM 1490.00 DM 1490.00 DM 998.00 DM 998.00 DM na * na * 550.00 DM 475.00 DM 150.00 DM

* not available

successor

With the desktop computer Geneve 9640, an unofficial successor to the TI-99 / 4A, produced by the American manufacturer Myarc, appeared in early 1987 for 998 DM.

The successor model is, in the strict sense, a technically improved clone of the TI-99/8 prototype. The Geneve 9640 was equipped with a TMS9995 16-bit main processor that was 95 percent software-compatible with the TMS9900, the RGB-compatible graphics chip that was software-compatible with the TMS9918A and allowed the display of 512 colors, a Yamaha V9938, 512 KB RAM, 128 KB dedicated VRAM and a The 64 KB ROM software emulator of the predecessor model resides in the permanent memory, with the help of which the plug-in modules of the TI-99 / 4A could be used on the Geneve 9640. The operating system used was the MDOS (short for Myarc Disk Operating System ) , which was specially programmed for the computer and supported graphical user interfaces . The Geneve 9640, capable of displaying 80 characters per line and operating at a clock frequency of 12 MHz, also had a real-time clock , voice output, a mouse connection, TI-99 / 4A-compatible joystick connections and a remote, IBM-PC-compatible keyboard.

hardware

The electronics of the TI-99 / 4A essentially consist of a main processor, several special components, a working memory and a permanent memory. These system components are attached to a motherboard and connected to one another via the conductor tracks of the system bus. With the exception of a few memory chips, all electronic assemblies are produced in-house. This corresponds to the corporate philosophy of TI at the time, which was based on the experience gained in the development and sale of pocket calculators. In addition, the housing, keyboard, interfaces and power supply are part of the computer's hardware.

Main processor

With the TMS9900, the TI-99 / 4A has a complex 16-bit main processor with DIP housing and 64 connection pins, which is considered a "quantum leap" in the history of microelectronics. The TMS9900 was the world's first 16-bit microprocessor implemented on a single chip. The TMS9900, which was ready for series production in 1976, belongs to the second generation of microprocessors developed by TI and replaced the successful 4-bit microprocessors such as the TMS1000 , which were mostly used for control purposes in electronic devices . The TMS9900 was not only used in the home computer sector, but also in the high-priced mini-computers of the TI-990 series - for example in the early models TI-990/4 (1976) and TI-990/5 (1979). In addition to the civil sector, the TMS9900 was also used in the military sector.

The TMS9900 is equipped with an arithmetic-logic unit that functions as a hard-wired electronic arithmetic unit , which is designed for processing 16-bit data words and calculating addresses. The CPU is also equipped with NMOS logic and can be clocked with frequencies of up to 3.3 MHz. In the TI-99 / 4A, however, the TMS9900 only runs at 3 MHz for reasons of synchronization with the graphics chip. This clock frequency is generated by the TIM9904 clock module or the TIM9904A of the same construction, which is connected to an external quartz crystal and works with four phase-shifted clock signals in the form of square-wave signals . These are generated from a basic frequency of 40 MHz using transistor-transistor logic . The TMS9900 takes 2–31 microseconds (µs) to execute a command. This results in an average working speed of around 0.3 million instructions per second (MIPS). The number of transistors implemented in the TMS9900 is around 8,000.

Die-Photo of a CPU of the type TMS9900 (1976)

The TMS9900 has an instruction set of 69 instructions including multiplication and division. This also includes the then unusual, step-by-step troubleshooting ( “single-step debugging” ) on a pure software basis X- jump command . The instruction set has five functional groups: instructions for data transfer, arithmetic instructions, logic instructions, processor control instructions and program control instructions. The TMS9900 command words can be 2–6 bytes. For data transfers and memory access, the CPU implemented in memory-memory architecture also has separate 16-bit bus structures that allow the management of an address space of 64 KB via direct memory access and memory mapping . In addition, the TMS9900 uses three internal 16-bit hardware registers for fast intermediate storage of data. These include the program counter (PC), the status register (ST) and the so-called “workspace pointer” (WP).

The WP, also known as "work area pointer" or "pointer register" in German, is special in that it stores its register contents not on the CPU itself, but externally in a special area of ​​the main memory ( "workspace" ). This CPU-RAM allows the use of a large number of up to 16 software registers, between which it is possible to jump back and forth without loss of data. In addition to the contents of the PC, ST and WP, ​​this includes the base address of the CRU control bus, the XOP address and eleven freely usable registers for data, addresses or a shift command counter . The possibility of jumping back and forth between the software registers facilitates the processing of interrupts as well as the quick context change between different register sets, e.g. B. between various subroutines. In principle, the WP even enables the computer to multitask . However, this is bought with a slight loss of speed, since when accessing the CPU-RAM, the corresponding memory address must first be transmitted by the WP and a read / write command must be carried out. The TMS9900 offers 17 hardware and 16 software interrupts, for a total of 33 interrupt levels.

Graphics chip

Game scene from Car Wars (1981)
in Graphics II mode
Game scene from Parsec (1982)
in Graphics II mode

The 8-bit graphics chip of the TI-99 / 4A was manufactured in three different versions: TMS9918A and TMS9928A for the 525-line format of the NTSC or SECAM standard and the TMS9929A ​​for the 625-line format of the PAL - Standard. To operate the computer with PAL televisions, however, an additional, separate HF modulator must be used.

The TMS9918A achieves a maximum resolution of 256 × 192 pixels, has a palette of 15 colors (plus transparency) and is able to display up to 32 sprites at the same time. Due to this high number of sprites and the associated collision detection capability , the TMS9918A was one of the most powerful graphics chips at the time. The size and resolution of the additional storage space required can be varied. 8 × 8, 16 × 16 and 32 × 32 pixels, each in monochrome representation, are possible natively. By superimposing sprites in different colors, multicolored objects with sprite properties can be generated.

The graphics chip, equipped with 40 connection pins, not only generates the video signal , but also manages the graphics memory of up to 16 KB required for storing, retrieving and updating the screen data . This also includes the memory space required for up to 256 alphanumeric characters, punctuation marks and graphic symbols of the freely programmable character set . The preset alphanumeric characters correspond to the 95 printable characters of the ASCII code (character codes 32–127 of the ASCII character table ). The graphic symbols can be combined to form simple block graphics . Since part of the main memory is used for the graphics memory, the size of the program memory available depends on the graphics mode used. A total of four graphic modes are available as required:

  • In text mode, 40 × 24 characters with a size of 6 × 8 pixels can be displayed. A color is available for the background and text. Sprites are not possible. About 3 KB of graphics memory are required for text mode.
  • In multi-color mode, all 15 colors and the use of sprites, but not text, are possible. The screen is divided into 32 × 24, i.e. 768 areas. These each consist of four 4 × 4 pixel blocks, the colors of which can be freely selected. The multi-color mode requires 1,728 bytes as graphics memory.
  • In the text and fuel-enabled Graphics I mode, an image is generated in maximum resolution, with the screen again being divided into 32 × 24, i.e. 768 areas with a size of 8 × 8 pixels. These can each take on two colors and be filled with either characters or graphic symbols. This requires up to 2,848 bytes of graphics memory. This graphics mode is the only one that can be programmed in TI BASIC.
  • In the text and fuel-capable Graphics II mode, the screen is divided into three areas with 256 areas each at maximum resolution. Each third of the screen has its own character set with up to 256 entries. If required, each of the 8 × 8 pixel 768 areas can be programmed individually as bitmap graphics , which, however, requires the use of machine language or GPL . Each of the eight lines of an area can take on two different colors. So all 15 colors can be used within one area. This uses up to 12 KB of graphics memory.

According to the data sheet, the three analog color outputs of the TMS9918A deliver the following levels:

Color code colour Y RY BY
0 transparent - - -
1 black 0% 47% 47%
2 medium green 53% 7% 20%
3 light green 67% 17% 27%
4th dark blue 40% 40% 100%
5 light blue 53% 43% 93%
6th dark red 47% 83% 30%
7th cyan 73% 0% 70%
8th medium red 53% 93% 27%
9 light red 67% 93% 27%
10 dark yellow 73% 57% 7%
11 light yellow 80% 57% 17%
12 dark green 47% 13% 23%
13 magenta 53% 73% 67%
14th gray 80% 47% 47%
15th white 100% 47% 47%

In the case of light red, it is noteworthy that converting the color difference signals to RGB would result in an inadmissible value of 113 percent for the red channel. The value RY should be a maximum of 80 percent. However, this is not a misprint in the data sheet. If the signals of the chip are measured with an oscilloscope , the table in the data sheet proves to be correct. An error in the chip design drives the red channel into saturation during a subsequent RGB conversion .

It should also be noted that at the beginning of the 1980s, only the cathode ray tube was available for displaying images on monitors or televisions . However, their playback function is not linear. This is why the values ​​are given a gamma correction factor which is 1.6 for cathode ray tubes in televisions (for comparison: 1.8 for Macintosh monitors and 2.2 for PC monitors). The colors of the TMS9918A appear paler on modern flat screens , unless this fact is taken into account.

The color "transparent" appeared as black on the TI-99 / 4A because the graphics chip's ability to work with an external video source was not used.

The illustrative colors in the table above take all of these details into account.

Sound chip

The TMS9919 is responsible for the sound output 8-bit sound chip of the TI-99 / 4A. The as "Complex sound generator" designated TMS9919 has three individually programmable tone generators and a noise generator , the same four tones or sounds to 16 can produce different volume levels. The distance between the selectable volume levels is 2 decibels, the maximum volume is 28 decibels.

The three tone generators work with square waves , the noise generator with pseudo-random noise (English "periodic noise" ) and white noise (English "white noise" ). The tone generators produce audible tones within a spectrum of five octaves, ranging from 110 Hertz to 44 Kilohertz. The tone length can be between 1 millisecond and 4.25 seconds. The TMS9919 has 16 connection pins and uses the DIN socket on the rear to transmit the audio signal to the loudspeaker of the connected output device.

I / O block

The TMS9901 is a multifunctional I / O module with 22 connection pins. It supports the CPU in input and output operations, such as input via the keyboard, the use of external storage devices or joysticks. Read out data can be forwarded to any location in the main memory via direct memory access. Internally, the TMS9901 has a priority scheduler , an encoder , a real-time clock , a control unit for communication with the control bus and three buffers for the intermediate storage of data.

Memory chips and memory organization

The main memory of the TI-99 / 4A consists of eight 1-bit DRAM chips of the type TMS4116 with 16 connection pins and a storage capacity of 2 KB each. In addition, there are two non-volatile 8-bit SRAM chips from Motorola , each with 128 bytes of memory and 24 connection pins. They are also known as “ scratch pads” and serve as CPU RAM. Due to their high access speed, the SRAM chips are considered to be high-speed storage.

The permanent memory of the TI-99 / 4A consists exclusively of mask-programmed ROM chips. He has two u. a. the operating system kernel ( "System Monitor" ) and the interpreter of the so-called "Graphics Programming Language" (GPL) containing 16-bit ROM chips with 24 connection pins and a storage capacity of 4 KB each. In addition, the computer has three charge-coupled 8-bit GROM chips ( "Graphics Read-Only Memories" ) with 16 connection pins and a storage volume of 6 KB each. These read-only memory chips, produced exclusively by TI, are primarily used to hold subroutines written in the GPL and are implemented using memory map technology. In addition to an 8-bit data bus, the GROM chips have a read-only memory which, with the help of mask-programmed firmware, emulates an on-board command counter ( “program counter” ). Internally, this takes on the task of setting and counting memory addresses instead of the corresponding CPU register.

This makes it possible to dispense with the central reading of the memory cells by the CPU via direct memory access, which is otherwise common with ROM chips. Instead, the address pointer of the on-board command counter initially sets a specific address from which memory contents are then continuously read out. These memory contents are stored in a local buffer memory for further use by the CPU. After each read operation, the address counter of the GROM chip is automatically increased without the need to set the address again. In this way, a large volume of data can be accessed relatively quickly via just one input. TI made it possible to dispense with the use of the high-speed ROMs that were common at the time, but expensive. Therefore TI had the invention of the automatically incrementing address counter built into the firmware of the GROM chip ( “auto-incrementing memory” ) patented.

The 64 KB address space is divided into eight 8 KB blocks each reserved by the operating system for different, predefined areas of responsibility. The operating system ROM may be a. Reserved for the control unit of the floppy disk drive, the RS232 interfaces of the PES and the printer control. It is sometimes referred to as "console ROM". The device driver ROM ( "DSR-ROM" for "Device Service Routines" ) was unusual for the time, as it allowed the use of peripheral devices without using up the main memory or making changes to the computer. It is sometimes referred to as “peripheral ROM”.

Memory usage of the TI-99 / 4A

Address range use
$0000-$1FFF Operating system or console ROM
$2000-$3FFF 32 KB RAM memory expansion
$4000-$5FFF Device driver or peripheral ROM
$6000-$7FFF Plug-in module ROM or RAM
$8000-$9FFF Graphics memory, GROM, sound and speech output, CPU-RAM
$A000-$BFFF 32 KB RAM memory expansion
$C000-$DFFF 32 KB RAM memory expansion
$E000-$FFFF 32 KB RAM memory expansion

System bus

The computer architecture of the TI-99 / 4A differs significantly from that of other contemporary home computers, because it is a hybrid of the classic 8-bit architecture (8-bit data bus width for special components and RAM) and 16-bit, which was not yet common in the home computer sector at the time Architecture (16-bit main processor, 16-bit data bus width for SRAM and ROM). The main processor communicates with the various electronic components via the data lines of the system bus , which consists of the three components data bus , address bus and control bus .

Data bus

The data bus is used to transfer data between the individual system components. With the two SRAM chips and the two ROM chips, only a small number of the system components are connected directly to the main processor via a bidirectional 16-bit data bus. Beyond this core area a functioning as Busconverter makes multiplexer for a reduction of the data bus width to 8 bits. In this way, all 8-bit system components such as graphics chips, sound chips or GROM chips can be controlled by the CPU with the appropriate word length. However, this serialization significantly reduces the execution speed of the overall system compared to computers with a pure 16-bit architecture.

The expansion port and module slot can also only be reached by the main processor via the slower 8-bit area of ​​the data bus. In addition, there is another limitation with the DRAM chips: the CPU can only access the areas of the main memory that are not currently used for video signal and image repetition when executing programs in TI BASIC or machine language via the time-consuming detour via the 8-bit graphics chip.

Address bus

The address bus unidirectionally transmits memory addresses between the main processor and memory chips for the purpose of passing on the information as to which memory cell is to be read or written next. The CPU stores the desired address as a binary pattern on the address bus before it is sent, which works with the 16-bit bus width typical for 8-bit architectures.

The various system components are controlled by the address bus with a variable word length. The 16 address lines of the expansion port enable the CPU to manage a max. 48 KB of extended RAM and peripheral devices with up to 16 KB of device driver ROM. The 13 address lines attached to the module slot allow the operation of plug-in modules with an address space of 8 KB. This additional memory can either be supplied by ROM or RAM chips. However, GROM chips whose memory is managed by an address decoder ( "Memory Address Decoder" ) were used far more frequently . The 4 KB of the two 16-bit ROM chips are covered by twelve address lines. Eight address lines are sufficient for the 256 bytes of the two SRAM chips.

There is a special feature with the GROM chips. Although these are memory chips, they are not connected to the address bus via their own conductor tracks. Instead, the address decoder is linked on the input side with the six more significant bits of the address bus and uses chip select signals to inform the two coprocessors for graphics and sound as well as the GROM chips who is taking part in the memory operations that are currently starting.

Control bus

The TI development team called the TI-99 / 4A's unidirectional control bus the Communications Register Unit (CRU). This synchronous 1-bit shift register is used by the CPU to control both internal and external system components via serial data transmission . For this purpose, control information is sent bit by bit to the corresponding system components, for example to regulate the direction of data flow on the system bus. In addition to read / write control, interrupts and bus access are also regulated from the control bus. With the aid of the status line, individual status bits can be sent to each individual system component to check operational readiness . System components can also be activated or deactivated in this way. In addition, the CRU is entrusted with the task of synchronizing the computer and peripheral devices, which is accomplished via hold, interrupt and acknowledgment signals.

The TMS9900 has three conductor tracks with their own connection pins, specially designed for the use of the CRU: CRUIN for reading out memory cells, CRUOUT ​​for sending data and CRUCLK for writing data. In addition, twelve conductor tracks of the address bus are used for the control bus.

casing

The original version of the TI-99 / 4A has a rectangular plastic housing "in a metallic look with a black keyboard", which is clad on the top with brushed aluminum and has a futuristic space-age design. The slots in the housing were adopted from the design of the TI-99/4. Behind it was a loudspeaker that was left out on the TI-99 / 4A. That's why they serve as ventilation slots for cooling the electronics. In addition, the computer has a main switch , a status display and a slot to accommodate plug-in modules , but no reset button . The calculator weighs 2.3 kg without the power supply and measures 25.9 cm × 38.1 cm × 7.1 cm (length × width × height). The power regulator located under the free area in front of the module slot tends to get very high temperatures during continuous operation. This part of the case was jokingly referred to as the "coffee cup warmer".

keyboard

The TI-99 / 4A's QWERTY mechanical typewriter keyboard has 48 alphanumeric keys and a layout that is far removed from today's standards. There is no version with a German keyboard layout. The keys on the main block are arranged in five rows. Only a function key to the right of the space bar is part of the equipment. Apart from the very wide space bar and the right shift key , all other special keys are the same size as the simple alphanumeric keys. A numeric keypad for entering large numbers of numbers is missing, as is a tab key in the main block. For this the computer waits with a lockable switchover lock .

The function key does not serve the usual functions such as help, search or delete, but just like the control key, the multiple assignment of individual keys. While the letter keys usually have double assignments, almost all of the numeric keys have even three assignments. To make operation easier, the multiple assignments are shown on a keyboard template above the keypad. The most important editing functions as well as some frequently used commands of the TI BASIC can be activated by pressing the function key and certain number keys at the same time. The arrow keys are unusual in that they are not located in a separate cursor block, but can only be activated via double-assigned letter keys in the main block. The keyboard is connected to the motherboard via a 15-pin connector and a corresponding cable bundle .

Double assignments via the function key

Letter key W E R T U I O P A S D F G Z X C
+ FCTN ~ [ ] - ? ' " : { } \ ´

Interfaces

The TI-99 / 4A has six interfaces . On the left there is a nine-pin Sub-D socket which can be used to connect joysticks, paddles or comparable digital control devices. Despite their external similarity, the assignment of the nine poles is not compatible with the standard set by the Atari joysticks at the time. Unlike most home computers, there is only one joystick connector. The expansion port is on the right. This is a circuit board connector with 44 contacts embedded in the housing , which is sealed with a protective cover when not in use. The expansion port enables a direct connection to the system bus. Floppy drives, printers and modems , but also memory expansions, etc. can be connected to the computer.

On the back there is another nine-pin Sub-D socket on the left, which is designed for connecting standard cassette recorders. To the right of the cassette interface there is a four-pin connector for the power supply unit. The computer has a five-pin (NTSC) or six-pin DIN socket (PAL / SECAM) on the right-hand side. Using this socket, the computer can be operated with a monitor or, via an additional RF modulator, with a television set. The audio signal is also output via the DIN socket. The module slot has 18 contacts that are intended to accommodate the circuit board connectors used in the plug-in modules.

Peripherals

TI-99 / 4A with two joysticks connected to the joystick port via a breakout cable (1982)

In addition to the peripheral devices specially developed by TI for the TI-99 / 4A, the so-called “sidecars” of the predecessor model TI-99/4 can also be used. In addition, there are other additions from third-party manufacturers such as A / D Electronics, Axiom, Boxcar Peripherals, CorComp, Doryt Systems, Horizon, ISC, Millers Graphics, Myarc, Navarone, Newport Controls, Percom Data and Triton, some of which were only available after the TI-99 / 4A shipped in 1983.

The date and place of manufacture of all TI products manufactured in the early 1980s can be determined by their serial numbers : These each consist of a number with up to six digits followed by a combination of three letters and a four-digit number. The letters ATAdenote the TI branch in Abilene, ATDstands for Austin, LTALubbock, ACHAlmelo (Netherlands) and RCIRieti (Italy). The first two digits of the following four-digit number refer to the calendar week of the corresponding year of production identified by the last two digits.

Peripheral Expansion System

TI-99 / 4A with TI voice module, TI color monitor plus start menu and Peripheral Expansion System (1982)

The sidecars turned out to be impractical when used with the TI-99/4 due to their high space requirements and the abundance of cables on the desk. As an alternative developed TI then the on the Winter Consumer Electronics Show 1982 presented "Peripheral Expansion System" (PES) with the type number PHP1200. The device with its own power supply has eight slots for the expansion cards of the peripheral devices to be connected, a slot for accommodating up to two 5¼-inch floppy disk drives with a single overall height, a fan for cooling and an interface card supplied for connection to the computer. The PES came on the American market in two almost identical, compatible versions in a sturdy metal housing. Adapted versions were produced for the European sales areas and the mains voltages that are common there . The German version was available in September 1983 as a package with the TI-99 / 4A for 1,500 DM. A total of 250,000 copies of the PES, which cost around USD 250, were sold.

The expansion cards, which were new in this form at the time, have solid metal or plastic housings together with a status display and have a 30-pin circuit board connector on the underside that connects to the PES. They work just as easily as today's plug-and-play cards and can be used as soon as they are inserted without having to install a driver . The following list provides an overview of the extensions produced by TI:

  • PHP1220 RS-232 interface card ( "RS-232 interface" )
  • PHP1240 drive controller card (Engl. "Disk Controller" )
  • PHP1250 5¼-inch disk drive ( "Disk Memory Drive" )
  • PHP1260 32 KB RAM memory card ( "32 kilobyte memory expansion" )
  • PHP1270 P code interpreter card ( "P code version 4.0" )
  • PHP1280 P code interpreter card with UCSD Pascal integrated development environment ( "Pascal Development System" )

RS-232 interface card

RS-232 interface card (1982)
Drive Control Card (1982)
Rear of the PES with slots for expansion cards (1982)
Front of the PES with slots for expansion cards (1982)
Front of the PES with 5¼-inch floppy disk drive (1982)

The offered at the time of 174.95 USD RS232 interface card has two connectors: A according to the eponymous RS232 executed standard socket 25 connection pins and two serial ports for connection to RS232C compliant peripherals and designed as a parallel port socket 16 connection pins. The driver software for implementing the transmission protocols is housed in a 4 KB ROM chip on the circuit board of the RS232 interface card and allows data transmission to be controlled between local and remote computers using the appropriate TI Extended BASIC commands.

A maximum of two peripheral devices can be connected to the RS232 socket at the same time using a so-called Y cable, whereby the data transfer rates of 110, 300, 600, 1,200, 2,400, 4,800 and 9,600 baud that can be set by the software  are relatively low. Higher data transfer rates can be achieved via the parallel 8-bit interface , which was not, however, pin-compatible with the Centronics standard that was widespread at the time . When using a suitable adapter cable, printers, plotters and terminals from third-party manufacturers equipped with a Centronics interface can be connected. A maximum of two RS232 interface cards can be operated simultaneously with the PES.

Drive control card

In the drive control card is one with a floppy-disk controller of type FD1771 from Western Digital as well as an 8-KB ROM chip equipped control unit to manage up to three 5¼-inch floppy drives. The floppy disk controller performs all disk operations and controls the motors and magnetic read / write heads of the connected drive mechanisms . The permanent memory contains the four device driver routines required for this. In addition, the control unit also manages the diskette table of contents with their indexed files. The tables of contents are stored in sectors 0 and 1 of the first track.

The drive control card can only be operated with the eighth slot, which is located directly next to the drive bay. The connection to the drive mechanism is made via a suitable cable that is connected to the 34-pin connector on the rear. Two more drives can be daisy- chained to the first floppy disk drive. Around USD 300 had to be invested for a drive control card including the plug-in module with the diskette operating system Disk Manager , which is indispensable for commissioning .

5¼ inch floppy disk drive

The 5¼-inch floppy disk drive, which cost around USD 400 at the time, has a floppy disk slot with a flap lock and a status display on the front. On the back there is a cable for connection to the internal power supply of the PES and another 34-pin cable for connection to the drive control card.

The drive mechanism uses a magnetic read / write head with an average access time of 463 milliseconds . The drive allows a data volume of up to 89 KB to be stored on one disk side ( Single Sided ) in single density ( Single Density ). 40 tracks with nine sectors each are used per disk side.

32 KB RAM memory card

The 32-KB RAM-memory card 16 has the company Mostek on originating 1-bit DRAM chips of the type MK4116 with connection pins 16 and a capacity of 2 KB. The additional DRAM chips increase the freely programmable main memory of the TI-99 / 4A to 48 KB RAM. This means that the computer has reached its highest level of expansion in terms of storage capacity. Using the mini memory plug-in module, however, a further 4 KB of SRAM can be added to the system, bringing the working memory to a total of 52 KB.

The additional main memory is connected to the data bus of the PES via eight data lines. As with the factory-installed main memory, data can only be written to or read from the memory cells of the expansion card with an 8-bit word length. The memory card has an automatic self-test function for hardware fault localization and is simply inserted into one of the slots of the PES for commissioning before the computer is switched on. The new price at the time was 300 USD.

P-code interpreter card

With the help of the P-code interpreter card, the high-level compiler language UCSD-Pascal can be operated with the TI-99 / 4A. Instead of an actual one, the P-code interpreter card only has a virtual CPU with its own hardware-independent instruction set, the so-called "pseudo machine", and one made up of a 2 KB ROM chip, a 4 KB ROM chip and eight 6 -KB-GROM-Chips existing permanent storage of a total of 54 KB . In addition to the software emulation of the hypothetical CPU, which is not based on any actually used microprocessor, it contains a convenient P-code interpreter that can process UCSD Pascal software developed for other systems.

The P-code interpreter card can only be used if, in addition to a 32 KB RAM memory expansion, a floppy disk drive or cassette recorder is connected to the computer. With the help of a switch on the back it can be activated before starting up the computer. If the card is activated, the P-code interpreter is initialized within 30–60 seconds after switching on. Then the command mode of the P-code interpreter is executed.

In addition to the P-code interpreter card, a UCSD Pascal software package was launched in 1982 for USD 499.95. It consists of the following components:

  • PHD5063 UCSD Pascal Compiler (converts programs written in Pascal into pseudocode , which is then translated into machine language by the P-code interpreter)
  • PHD5064 UCSD Pascal System Assembler / Linker (software package with programming environment for assembler language and linker )
  • PHD5065 UCSD Pascal System Editor / Filer / Utilities (software package with 40-character text editor and modern floppy operating system including time stamps and auxiliary programs )

Other storage devices and storage media

Program recorder

TI program recorder with side dials and connections (1982)
Audio example of a TI-BASIC file

The TI-99 / 4A could be operated with commercially available cassette recorders ; But TI did nevertheless a specially tailored to the computer program recorder (Engl. "TI Program Recorder" ) with a data transfer rate of 450 baud out. The device with the type number PHP2700 has all the usual properties of a cassette recorder, but is also optimized for use as a storage device. The price was $ 70.

The program recorder is tailored to compact cassettes in the C60 format with 30 minutes playback time per side and was offered in two variants adapted to the design of the two versions of the TI-99 / 4A. In addition to buttons for record, play, rewind and forward, pause and eject, it has two rotary controls for volume ( "Volume Control" ) and tone ( "Tone Control" ), a built-in loudspeaker, a standard microphone and one Pause button. In addition, the program recorder is equipped with a counter and has three connections for a connection to the console ( "Ear Phone Jack" , "Mic Jack" and "Remote Jack" ). The power is supplied internally via four baby cells with a total of 6 volts or externally either via a direct current adapter ( "DC adapter" ) or the power grid ( "AC input" ).

The device was known for its reliability, but also its slowness. Both properties result from the redundant recording method, which deviates from the Kansas City standard . All data records are recorded twice and checksum bytes are also used to detect data transmission errors. To read in the data, the timer of the TMS9901 measures the exact lengths of the half-waves of the audio signal and transfers them in binary code that the computer can understand . A long half-wave (689.37 Hz) means a zero, while two short half-waves (1379 Hz) mean a one. When recording a new file, the magnetic tape is first fast forwarded a few seconds and then a continuous tone is recorded at a constant frequency.

The typical TI sound resulting from this process was familiar to every user and was even used in the leading medium of television at the time. The specialist book author and TI-99 / 4A expert Rainer Heigenmoser worked as a technical advisor in the three-part German-language ARD television series Bastard (1989), which was the topic of computer crime . A fax machine is shown at one point. The overdub used for the operating noise during fax transmission does not come from a fax machine, but from a TI-99 / 4A that stores data on a cassette.

Plug-in modules

Plug-in module circuit board with GROM chip and circuit board connector (1983)

In contrast to the storage media prevailing at the time, such as compact cassettes or floppy disks, the plug-in modules ( Solid State Software Cartridges or Command Modules ) do not have the annoying loading times due to the use of read-only memories. However, in contrast to these data carriers, the plug-in modules cannot be copied and can only be written to when using EPROM or battery-buffered RAM chips. The plug-in modules were also relatively expensive due to the relatively high production costs of around USD 6 per unit.

The plug-in module boards, protected by rectangular plastic housings, have a board connector with 18 contacts and usually contain a 6 KB GROM chip. In contrast to conventional practice, this is not copied into the comparatively small main memory of the TI-99 / 4A, but used as an additional memory bank. The so-called “multimodules” have several GROM chips with additional programs, between which you can choose using the address decoder. A total of up to 30 KB GROM can be added. Therefore there are five slots on the plug-in module boards. You can also add up to 8 KB EPROM or 4 KB RAM. TI signed contracts with a number of third-party vendors such as Imagic, Milton Bradley, Walt Disney and Addison-Wesley, which allowed these companies to develop their own cartridge software, with the manufacture of the patented GROM chips and the distribution of the finished cartridges in their hands from TI remained.

Other output devices

Color monitor

TI produced a 10-inch color monitor ( "TI Color Monitor" ) with a maximum resolution of 720 × 300 pixels specifically for the TI-99 / 4A . The device with the type number PHA4100A has its own power supply as well as numerous controls, for example for setting color intensity, contrast or brightness. It was produced in its own versions for the NTSC, PAL and SECAM standards. It cost around $ 400.

Language module

TI developed a speech module ( "Solid State Speech Synthesizer" ) for its predecessor TI-99/4 as early as 1979 , which equipped the computer with the ability for artificial speech output at a price of around 100 USD and also with the TI-99 / 4A can be used. The voice synthesis was a specialty of TI and was explored in a specially established department. However, it was still in its infancy at the time.

An 8-bit TMS5200 voice chip , which belongs to the second generation of the special chips for voice synthesis developed by TI, is built into the voice module . The TMS5200 has a buffer for voice data and 4-bit control bus structures. In addition, the voice module has two specially developed 16 KB voice ROM chips of the type TMS6100 with highly compressed voice files. These are made up of digital representations of voiced and unvoiced phonemes that can be called up again and again and thus save memory . This was called " Linear Predictive Coding " by the TI developers . These language files can be read in from the language chip via direct serial access. The voice chip simulates a filter model of the vocal tract and feeds it with the imported data in order to generate a synthetic waveform . The output of this filter model goes through a digital-to-analog converter , which is then used as an audio signal and passed on to the computer's audio output. The language ROM chips also have 373 preprogrammed words that can be called up directly from the TI BASIC and which can be combined to form simple sentences. Some arcade games such as Parsec make use of the capabilities of the language module to create a realistic gaming atmosphere.

printer

In autumn 1982 TI launched a black and white matrix printer ( "TI 99/4 Impact Printer" ) with the type number PHP2500 for around USD 750 . This is a standard Epson MX80 printer bearing the TI logo . The device can handle four fonts and prints either 40, 66, 80 or 132 characters per line at a printing speed of 80 characters per second. Graphics can be put on paper in two different resolutions: 480 pixels per line ( “normal density” ) or 960 pixels per line ( “dual density” ). On the top there are control buttons for sheet feed, line feed and direct printing. The device has a serial RS-232 socket and a parallel interface on the rear.

Other input devices

TI produced dual joysticks ( "Wired Remote Controllers" ) with the type number PHP1100 for the TI-99 / 4A, which could not be connected to any other computer without an adapter . Two joysticks offered in the package were connected to the joystick connection of the computer via a common cable and their signals were continuously queried by the I / O module, accepting reduced response times. These control units each have a control stick with eight possible settings and a wide fire button. They cost around $ 35.

Remote data transmission

For the data transmission developed specifically TI one as early as 1979 acoustic executed modem (Engl. "TI Telephone Coupler" ), which can transfer data at a speed of 300 baud. The device with the type number PHP1600 has a power connection and two slide switches for switching on / off, initializing the test run and setting the data transmission method. The substance may have alternating operation (Engl. "Half-duplex" ) and back-operation (Engl. "Full-duplex" ). For operation, a connection to the computer must be established via one of the RS-232 interfaces. The acoustic coupler cost around USD 200 at the time.

software

At the end of 1983, around 800 different program titles were available for the TI-99 / 4A on various data carriers, including programming languages , application software , educational software, and computer games . The majority of these programs (approx. 700) were provided by licensees , the rest comes from Texas Instruments itself. Since only about every tenth owner of the TI-99 / 4A bought the expensive PES with the corresponding floppy disk drive, the software was mainly on plug-in modules released. Even after the official end of production, new games for the computer, for example from Atarisoft, were released for a few years.

All of the system software required to operate the TI-99 / 4A, including the BASIC interpreter, is stored in the built-in read-only memory and is therefore ready for use immediately after switching on without booting .

System programs

Operating system kernel and system routines

The configuration of the hardware of the TI-99 / 4A and the built-in TI BASIC takes over from the responsible for data, device and process management kernel existing as well as numerous system routines operating system . This includes the initialization routine after switching on ( "power up" ) and various mathematical functions on the GROM chips. The ROM chips contain the system programs for executing interrupts for screen layout, keyboard queries and operation of peripheral devices, for controlling the cassette interface and various auxiliary routines, for example for calculating floating point numbers. After switching on the computer, all entry points ( pointers ) and all existing GROM modules are initialized, the device driver for the cassette recorder is configured and the start screen and start menu are then generated.

Floppy operating systems

To operate the TI-99 / 4A with 5¼-inch diskette drives, the Disk Manager diskette operating system, which is not supplied with the diskette drives and is supplied on a plug-in module, was developed. This floppy operating system can be used to format floppy disks and manage files (save, delete, copy and rename). Up to 127 files can be accommodated on each disk side. It is also possible to provide files with write protection and to carry out function tests for the floppy disk drives.

A later version of the disk system software, released in March 1983 under the title Disk Manager 2 , allows both sides of the disk to be used without manually turning the disk. In order to take advantage of this possibility, the user had to have the appropriate devices from third-party manufacturers, as TI itself did not offer drives with the required number of two read / write heads.

Native programming languages

TI BASIC

TI BASIC start screen with sample program

TI BASIC acts as both a user interface and a programming environment and has 82 commands, instructions , functions and variables . If it is selected in the Start menu, the startup message appears on the screen TI BASIC READYand the waiting for input prompt the command mode (Engl. "Command Mode" ). In addition, TI BASIC knows the programming mode ( "Edit Mode" ) and the program execution mode ( "Run Mode" ).

Pressing the Enter key causes the interpreter to execute commands. The programming mode can be activated by using line numbers at the beginning of the command line. The cursor can be maneuvered to any position on the screen using the arrow keys . The program RUNexecution is initiated by entering the command. Running programs can be stopped by pressing the break button . The computer is then back in command mode. TI BASIC can be exited either with the QUITcommand, which irretrievably deletes the program memory, or the BYEcommand, which allows the contents of the program memory to be called up later. Both commands lead the user back to the start screen.

TI-BASIC programs can only be stored in the areas of the main memory that are not used as graphics memory. The core of the TI-BASIC interpreter is in the ROM memory area from $18C8to $1C9A. The ROM chips also contain a jump table for the TI-BASIC routines in the GROM chips. Together, the TI-BASIC interpreter and routines have a storage volume of 14 KB.

Graphics Programming Language

The Graphics Programming Language (GPL) is a high-level instruction language developed by TI with a total of 59 instructions. The main task of the GPL is to provide a professional programming environment to use all hardware features of the on-board chipset, some of which are not accessible in TI BASIC. With the help of the GPL, for example, high-resolution bitmap graphics can be programmed and the sound generation options of the TMS9919 sound chip can be fully exploited.

Less convenient than TI BASIC, but more user-friendly than assembly language, the GPL, which allows direct access to the graphics memory via a special buffer, uses many commands identical to the command set of the TMS9900. As a "very close to the processor" intermediate language, it is therefore considerably faster when executing programs than the TI-BASIC interpreter. However, this property is rarely used in everyday applications, because the GPL, which is not mentioned in the TI-99 / 4A user manual and for which there was no programming manual authorized by TI on the free market, was not intended as a user interface. In the basic configuration, the computer can only be operated with TI-BASIC commands entered via command lines.

Despite its proximity to the processor, the GPL code with a total of 12 KB ROM cannot be executed directly by the TMS9900, but only using the built-in GPL interpreter. This occupies the ROM memory area from $0024to $08FF. The GPL interpreter is programmed in assembly language. In order to prevent the creation of pirated copies and the production of unauthorized software by third parties, he does not copy GPL subroutines into the freely accessible main memory before execution, but executes them directly in the GROM, saving space and protecting against unauthorized access.

The boundaries between GPL and TI-BASIC interpreters are fluid, as individual GPL commands such as PARSE, CONTor RTNBonly for the BASIC interpreter, but not the main processor can understand. Since TI BASIC is programmed exclusively in GPL code and BASIC programs have to be processed by both the TI-BASIC and the GPL interpreter before they can be executed, the BASIC dialect of the TI-99 / 4A is in comparison to slower than other home computers.

Optional high level programming languages

TI Extended BASIC

Shortly after the TI-99 / 4A was launched, TI recognized the slowness of the double interpreted TI BASIC as a problem. The BASIC expansion TI Extended BASIC was therefore released in the summer of 1981. In West Germany it was only available from 1984 and was sold under license by Mechatronic in Sindelfingen .

The TI Extended BASIC, which is largely downwardly compatible, offers a range of additional capabilities and an instruction set that has been expanded by 35 commands, instructions, functions, subroutines and logical operators compared to the basic version . It has an autoboot function, allows the use of subroutines in machine language and the display of up to 28 sprites. Strings can contain up to 154 characters and variables can contain up to 15 characters. In addition, TI Extended BASIC allows very convenient error handling, increases the number of dimensions available for fields ( "arrays" ) from three to seven and even provides commands for copy protection measures . In addition, several commands can be entered in a single program line to save memory. Since most of the TI Extended BASIC is written in machine language instead of in GPL code, the execution of programs is noticeably accelerated. The increase in speed is roughly twice that of the TI BASIC. Because of these properties, the TI Extended BASIC was compared by the specialist book author Rainer Heigenmoser with a luxury model from the British car manufacturer " Rolls Royce ", while the original TI BASIC reminded the author more of a small car like the " VW Beetle ".

With 32 KB ROM, TI Extended BASIC is extremely extensive and takes up another 2 KB of the working memory. This means that only 14 KB are available for graphics and program memory, which leads to a noticeable reduction in programming options. However, a memory expansion is not absolutely necessary for operation, provided that memory-saving programming techniques are used.

TI FORTH

TI FORTH is a dialect developed by TI of the stack-based , assembly-related and therefore fast high-level compiler language Forth . In addition to an operating system, TI FORTH provides a diskette-based integrated development environment with 64 characters per line, high-resolution bitmap graphics and interrupt routines. In addition to a 32 KB RAM memory expansion, TI FORTH also requires the editor / assembler plug-in module. Another Forth version was developed by Wycove Systems.

TI LOGO and the continuation TI LOGO II , which comes with an extended command set, printer functions and additional graphic capabilities, are also dialects of the high-level functional interpreter language of the same name, produced by TI. They serve to impart mathematical, logical and communicative skills to children as well as their practice in using computers. A 32 KB RAM memory expansion is required for operation with compact cassette, floppy disk or plug-in module. A greatly simplified trial version with limited programming options called Early Learning LOGO Fun could also be operated without a memory expansion.

TI PILOT

Also TI PILOT is a realized TI offshoot of interpreter-level language of the same name and enables the development of exercises, tests and interactive learning programs for computer-based learning. This programming language can only be operated with a 32 KB RAM memory extension, floppy disk drive and P-code interpreter card.

UCSD Pascal

Assembly language

An optimal utilization of the hardware of the TI-99 / 4A is only possible through the use of assembler language and a translation program (English " assembler " ), which converts the program instructions of the source text ( "source code" ) into machine language. TI offered a corresponding software package called Editor / Assembler , which included a cartridge, two floppy disks and a comprehensive operating manual. In addition to the editor and assembler, the software also contained a debugger for eliminating programming errors.

Programs in assembly language are much faster than those in higher programming languages and have the advantage over the even faster machine language that their instruction set can be handled more easily through the use of understandable and easily remembered abbreviations ( " mnemonics " ). Most programming beginners, however, preferred the less powerful, but easier to use, higher programming languages ​​such as Pascal or BASIC.

Application programs

A number of application programs have been created for the TI-99 / 4A, but many of them can only be operated with a 32 KB RAM memory extension and a floppy disk drive. This applies to file management programs such as Personal Report Generator and Personal Tax Plan as well as to the word processing program TI Writer or the spreadsheet program Microsoft Multiplan .

One of the most popular plug-in modules was the Mini Memory memory expansion , which also contains auxiliary programs such as a machine language monitor. Mini Memory equips the computer with 14 KB of additional memory, 6 KB of which is allocated to the GROM and 4 KB to the simple ROM. In addition, it is equipped with 4 KB battery-buffered SRAM. Shorter BASIC and machine language programs can be saved directly on the module without additional storage devices. Alternatively, TI-BASIC subroutines and a troubleshooting program can also be started. When using a 32 KB RAM memory card, Mini Memory allows direct access to its additional RAM.

The telecommunications program Terminal Emulator II , which was also published on the plug-in module and which enables the computer to be networked via an acoustic coupler, also enjoyed great popularity . In addition, the telecommunication software expands the application possibilities of the speech module with additional functions.

Tutorials

Control data logo

One of the most popular learning programs for the TI-99 / 4A was the Miliken Home Math Series with titles that were devoted to teaching basic arithmetic, percentages and decimal fractions. Also Addison-Wesley sat on educational software on mathematics and brought the cartridges of computer Math Games out series. The Minnesota Educational Computing Consortium developed learning programs for the humanities, social sciences, and science. The Control Data Corporation did for high school graduates of all ages and disciplines which Plato courseware series out. Scott Foresman, a publisher specializing in primary school children, published learning programs with artificial speech output, which were primarily aimed at improving reading skills.

TI itself focused on spelling and brought a six-stranded series entitled Scholastic Spelling , a then futuristic acting program for synthesized voice called text-to-speech and a practice program called Touch Typing Tutor for learning touch writing out. The graphically elaborate title Microsurgeon with its unusual game mechanics represents a mixture of arcade game and learning program .

Games

Parker logo
SEGA logo
Imagic logo

The 40 or so arcade games that appeared on plug-in modules were the most popular game genre for the TI-99 / 4A. The most popular arcade games, which typically cost anywhere from $ 11 to $ 45, included TI-produced titles such as Alpiner , The Attack , Blasto , Car Wars , Chisholm Trail , Choplifter , M * A * S * H , Munchman , TI Invaders , TI Trek and Tombstone City . The shoot 'em up Parsec from 1982 is considered the best game or even the “ killer application ” for the computer. Some particularly popular titles were also published on floppy disk for just under USD 20, but required a 32 KB RAM memory expansion in addition to a floppy disk drive.

The most successful third-party games included ported titles such as Dig-Dug , Donkey Kong , Jungle Hunt , Moon Patrol , Pac-Man, and Pole Position by Atarisoft (with an alternative case design), Q-Bert by Parker Brothers , Buck Rogers, and Star Trek by Sega , Space Bandits from Milton Bradley , the Frogger Clone Princess & Frog from Romox and Super Demon Attack from Imagic .

The most successful strategy game was Hunt the Wumpus . Backgammon , blackjack and poker and video chess were available for board games . Sports fans could have fun with titles like football or indoor soccer . The first flight simulation was Dow-4 Gazelle by John T. Dow. With bankroll one was from want Polyoptics also economic simulation published. The biplane aerial combat simulation Spad XIII , which was only published in 1987 and represents the first real 3D flight simulation for the TI-99 / 4A, also comes from the same company .

Adventures were also a popular genre of games. Above all, the titles by Scott Adams such as Ghost Town , Mystery Fun House or Voodoo Castle , which can be found on a compact cassette or diskette , should be mentioned in this context. The graphically lavish RPG adventure Tunnels of Doom , on the other hand, was so extensive that it had to be delivered on two data carriers.

See also : Category: TI-99 / 4A game .

Magazines

Several national and international magazines dealt with all questions about the TI-99 / 4A and provided their readers with test reports, purchase advice, building instructions, repair tips, classified ads and program printouts for games, applications and auxiliary programs.

English speaking world

The 99'er magazine was the most important magazine for the TI-99 / 4A and appeared from May 1981 initially every two weeks, from November 1982 then once a month under the full title 99'er Home Computer Magazine . The main focus was on the programming languages TI LOGO and TI PILOT . Interspersed crossword puzzles and cartoons provided for a loosening up. The 99 magazine was taken off the market in November 1983 .

The magazine MICROpendium , initially published under the title Home Computer Compendium , appeared monthly from February 1984 to June 1999 in Round Rock (Texas). It thus filled the gap left by the 99 magazine. With its emphatically neutral reporting, a simple black and white layout and a low price of 1.50 USD, the MICROpendium was able to hold its own for 15 years, but ultimately had to be discontinued due to insufficient sales.

German-speaking area

From 1983 to 1987 the Fiedler-Verlag in Vienna published the TI-99 Journal on a monthly basis . For 11 DM it had a multi-colored front page and also contained articles about other TI products. From the beginning of 1984 to 1987, the TI-Aktuell-Verlag in Lohhof, then later by the München-Aktuell-Verlags-GmbH, published the magazine TI-Revue, which was published at irregular intervals approximately every two months : The magazine for TI PC & TI- 99 / 4A for initially 4.80 DM. The specialist publisher Reinhold Hasse from Bendorf also published the TI specialist magazine , which dealt with the TI-99 / 4A and the programmable pocket calculator TI-59 .

In addition, the periodical TI-99 Software was self-published from 1981 with reports on current developments in the field of software for all TI home computers. In 1982 the magazine was first renamed TI Software Home Computer Magazine - trade magazine for users of the TI-99 / 4A . From 1983 the cumbersome addition was removed from the title of the magazine.

emulation

Over the years, numerous emulators of the TI-99 / 4A have appeared on various hardware platforms . In the 1990s they were popular on the IBM PC or the Commodore Amiga , but also on other computers. After these carrier systems became technically obsolete, new emulators were developed for more modern computers. There are four regularly updated emulators of the TI-99 / 4A on the Internet, some of which run on the current, in some cases somewhat older versions of the widely used MS Windows , OS X and Linux operating systems .

Current emulators

Home Screen of the TI-99 / 4A Emulator V9t9 (2014)

The emulator PC99 or PC99A was written by Greg Hill, Mark van Coppenolle and Mike Wright from the US company CaDD Electronics for IBM PC compatibles . Both the standard version PC99 and the accelerated version PC99A run under the operating systems PC DOS 5.0 (or higher), Windows 95 and Windows 98 . We recommend using at least one Intel 80486 with a clock frequency of 66 MHz. In addition, computers with CPUs of the types Pentium II , III , and IV or AMD K6-III can be used. Additional system requirements include a VGA video card , free hard disk space of at least 10 MB and a 3½-inch floppy disk drive.

The emulator V9t9 was programmed by Edward Swartz in Java code and can be downloaded as freeware from the Internet. The scope of services includes u. a. UCSD-Pascal, a P-code interpreter and an emulation of the TI matrix printer. The V9t9 runs on the MS Windows, OS X or Linux operating systems. The Win994a-TI-99 / 4A simulator comes from Cory Burr and is also available as freeware. He works on modern PCs under MS Windows. Finally, the MESS emulator system supports both the TI-99/4 and the TI-99 / 4A including the language module and expansion cards, although the corresponding ROM content is required for their emulation.

reception

Contemporary

The TI-99 / 4A received mostly positive reviews in the trade press and was even described as “one of the best home computers” that “has been on the market so far.” The computer received praise for its user-friendliness , its hardware expandability, and its opposite the previous model improved keyboard, its convincing color and sound capabilities, its ability for speech synthesis, its "compact [s], slim [s]" design, its robustness, its versatility and the extensive range of software. In addition, the existence of several computer magazines exclusively related to the TI-99 / 4A, such as the 99'er magazine or the TI specialist magazine, and the resulting easy availability of information on the computer were positively highlighted.

However, the still too small size of the new keyboard as well as its numerous multiple assignments, the thermal management of the internal power regulator, the below-average sound capabilities, the limited set of commands of the TI BASIC and the low operating speed of the TI BASIC interpreter, reminiscent of the British cheap computer Sinclair ZX81 , were criticized .

Retrospective

TI-99 / 4A as an exhibit in the Musée Bolo of the ETH Lausanne
TI headquarters in Dallas, Texas
Power regulator of the TI-99 / 4A without electrical fuse

The TI-99 / 4A is mentioned as an important home computer in almost all technical-historical overview presentations. Many engineering museums exhibit the computer, and it can also be found on many websites related to the history of home computers. In addition, there is an active retrocomputing scene in favor of the preservation of well-preserved specimens and other products connected to the computer . This means that the TI-99 / 4A has a firm place in the collective memory , although it is not as highly valued as the C64, Apple II , Sinclair ZX Spectrum or the Atari home computers .

Three aspects are typical of the technical history of the TI-99 / 4A. Firstly, it is considered technologically advanced, which is mainly attributed to its 16-bit CPU and the "excellent graphics properties for the time". Second, due to the peculiarities of its computer architecture, the computer is often viewed as an exotic "outsider" whose development has ended in an evolutionary dead end. Third, the TI-99 / 4A is considered to have ultimately failed in the market despite its respectable sales figures and has even been described as “perhaps the most hapless system on the home computer market”. This finding goes hand in hand with intensive research into the causes of this failure, which awakened memories of the 1961 bankruptcy of a Bremen car manufacturer , which heralded the end of the economic miracle :

“The TI-99 / 4A was one of the most comfortable and easy-to-use home computers ever to hit the market. The Borgward of the computer industry. "

- Dietmar Eirich u. Sabine Quinten-Eirich: The Heyne Computer Lexicon (1984)

The TI-99 / 4A's comparatively short market presence cannot be attributed to a single cause. Rather, a whole bunch of different misconduct led to the premature cessation of production of the computer. These include marketing errors, design errors, inadequate system documentation, certain peculiarities of TI's corporate culture and the preference for plug-in modules as the main storage medium.

Marketing mistake

TI made some serious marketing mistakes. Sales manager Turner relied almost exclusively on price reductions, instead of explaining to potential buyers the undoubted technical advantages of the TI-99 / 4A, such as the powerful 16-bit main processor, through suitable advertising measures. Considering the use of the TMS9900, which is around five times more expensive than conventional 8-bit CPUs at USD 20, and the associated high production costs, this is all the more astonishing. Nevertheless, TI embarked on a risky price war with the low-cost supplier Commodore, led by Jack Tramiel , and suffered a bitter defeat. In this context, a rather colloquial comment by the then Spectravideo managing director Harry Fox has become famous : "TI got suckered by Jack" (German translation: "TI was tricked by Jack").

Design flaw

The TI-99 / 4A suffered from a number of design flaws, the first being the double interpreted and therefore slow TI BASIC. In the benchmark tests usually carried out in BASIC at the time, the computer performed poorly despite the 16-bit CPU and ended up behind competing models such as the VC20, C64 or Apple II.

Storage organization also had its disadvantages. The 16 KB working memory served as graphics and program memory at the same time. In the high-resolution and therefore graphics- memory-intensive Graphics II mode, for example, only 4 KB were available for the program memory . More extensive TI-BASIC programs can therefore only be implemented in the less powerful Graphics I mode. Programming in machine language also required a very expensive memory expansion. In addition, such external memories could only be addressed with 8 bits by the 16-bit processor. The multiplexer, acting as a bus converter, converted each corresponding 16-bit access of the TMS9900 into two 8-bit accesses to the external memory. The wait states generated in this way noticeably reduced the working speed of the computer.

Due to the unsuitable keyboard layout for typing with the ten-finger system, the TI-99 / 4A could not establish itself as an office computer. In addition, the power regulator built into the console was not fitted with an electrical fuse, which increased the risk of electric shock. On top of that, the joystick connection was not Atari compatible and therefore did not meet the de facto standard of the time. Those who switched from other systems had to purchase new joysticks, which made the computer less attractive.

System documentation and software development

TI wanted to maintain sole control of software development to maximize profit. The top management therefore operated a business-damaging secrecy against the express advice of chief developer Bynum and renounced an open documentation of the operating system, GPL and computer architecture. This made software production more difficult for third-party providers unless they negotiated costly and profit-minimizing cooperation agreements with TI. Anyone who succeeded in developing commercial programs for the TI-99 / 4A was threatened with legal action. This approach deterred professional software houses as well as the creative hacker scene from dealing with the computer and its already little common CPU. Although the concept of a closed architecture was initially relaxed in the summer of 1981, it was resumed after the onset of the price war with Commodore in September 1982. It was not until 1985 that a West German publisher published a complete listing of the operating system, including the GPL routines, which was not supported by TI.

The company management also believed that it could single-handedly fulfill all of the customer's program requirements. Around $ 20 million is invested in software development each year. On the other hand, the licensing and porting of tried and tested user software such as Microsoft BASIC , Visicalc , WordStar and many games, which was common at the time and expected by customers, was dispensed with. As a result, the software developed for the TI-99 / 4A, with the exception of the tutorials, remained rather mediocre.

In 1983, realizations of Steven Spielberg 's globally successful movie ET - The Extra Terrestrial were developed for various hardware platforms, including the TI-99 / 4A and the market-leading Atari 2600 game console . When Spielberg happened to find out about the significantly lower quality of the Atari 2600 version, he simply withdrew the license from TI for fear of financial losses. The Atari 2600 version of ET the Extra-Terrestrial became one of the biggest flops in video game history and is now considered the epitome of the video game crash that began that same year .

Corporate culture

Lubbock, Texas, seat of the consumer electronics department from 1977

TI's corporate culture, which was then characterized by conservatism and self-referentiality , also contributed to the failure of the TI-99 / 4A. Out of arrogance, the technology giant refrained from developing a conventional 8-bit microprocessor based on the example of smaller but highly innovative manufacturers such as Zilog , MOS Technology or Intel , although the trend was clearly in the direction of 8-bit architectures. Since the company philosophy ruled out the use of third-party microprocessors and the company's own 16-bit CPU could not establish itself on the market, the planning of the TI-99 / 4A was not based on performance features that could be achieved or customer requirements, but on a computer that would match the TMS9900 although TI had not even developed suitable 16-bit coprocessors at the time. TI was also unable to produce cheaper chips for the TI-99 / 4A in its own semiconductor factories and thus achieve a reduction in production costs.

The company's top management was also convinced that they could do without enticing experienced computer technicians. This aspect of the corporate culture of the time is evident in the 1977 relocation of the headquarters of the entertainment electronics department from the megacity of Dallas to the sleepy cotton metropolis of Lubbock. For established computer experts from the liberal milieu of California's Silicon Valley , the prospect of a life in the deepest Texas province was usually no incentive to switch to TI. When developing the TI-99 / 4A, there was no outside spirit that would critically question the established corporate philosophy.

Cartridges and pirated copies

For months after its launch, TI did not offer any external storage devices for the TI-99 / 4A, not even a program recorder. Instead, the group initially relied almost exclusively on the relatively expensive plug-in modules. The young people, who formed an important group of buyers, could often not afford them and therefore preferred home computer systems whose software appeared on the cheaper compact cassettes or floppy disks. These storage media also had the advantage that the pirated copies that were common among young people at the time were easier to make and to exchange with one another. Plug-in modules, however, prevented this practice.

Literature (selection)

English

  • Ronald G. Albright: The Orphan Chronicles. San Dimas: Millers Graphics 1985, ISBN 0-931831-01-6 .
  • Raymond J. Herold: Compute! 'S Guide to TI-99 / 4A Sound and Graphics. Greensboro: Compute! -Publications 1984, ISBN 0-942386-46-9 .
  • Gary Phillips et al. David Reese: The Texas Instruments User's Encyclopedia. Los Angeles: The Book Company 1984, ISBN 0-912003-15-4 .
  • C. Regena [d. i. Cheryl R. Whitelaw]: Programmer's Reference Guide to the TI-99 / 4A. Greensboro: Compute! -Publications 1983, ISBN 0-942386-12-4 .
  • William B. Sanders: The Elementary TI-99 / 4A. Chatsworth: Datamost 1983, ISBN 0-88190-247-0 .
  • Brian Starfire: The Best Texas Instruments Software. New York: Beekman House 1984, ISBN 0-517-42476-2 .
  • Brian Starfire: The User's Guide To Texas Instruments TI-99 / 4A Computers, Software & Peripherals. New York: Beekman House 1983, ISBN 0-517-41450-3 .

German

  • Heiner Martin: The operating system of the TI-99 / 4A intern. Baden-Baden: Verlag für Technik und Handwerk 1985, ISBN 3-88180-008-5 .
  • Alma et al. Johann Peschetz: 99 Special I: Programming manual for advanced users of Texas Instruments home computers. Freising: TI Learning Center 1983, ISBN 3-88078-043-9 .
  • Georg-Peter Raabe u. Klaus-Jürgen Schmidt: Play, learn, work with the TI-99 / 4A. Düsseldorf: Sybex 1984, ISBN 3-88745-039-6 .
  • Karl P. Schwinn: TI-99 Tips & Tricks: A treasure trove for TI-99 users. Düsseldorf: Data-Becker 1983, ISBN 3-89011-006-1 .
  • Guido Pahlberg: TI-99 / 4A: color, graphics, sound, games. Vaterstetten: IWT Verlag 1983, ISBN 3-88322-045-0 .
  • Texas Instruments Deutschland GmbH (ed.): TI-99 / 4A: Create game programs yourself. Part 1. Freising: Texas Instruments Deutschland GmbH Learning Center 1984, ISBN 3-88078-047-1
  • Texas Instruments Deutschland GmbH (ed.): TI-99 / 4A: Create game programs yourself. Part 2. Freising: Texas Instruments Deutschland GmbH Learning Center 1984, ISBN 3-88078-048-X

Web links

Commons : Texas Instruments TI-99  - collection of images, videos and audio files

General information

Games encyclopedia

Current emulators

  • PC99 / PC99A emulator for IBM-PC compatible
  • V9t9 emulator for the operating systems MS-Windows, OS X and Linux
  • Win994a-TI-99 simulator emulator for the MS-Windows operating system
  • MESS multisystem emulator for the operating systems MS-Windows, OS X and Linux
  • TI-99 / SIM emulator for Linux, OS X and MS-Windows

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This article was added to the list of excellent articles on March 7, 2015 in this version .