Atari 400/800/XL/XE a series of 8-bit home computers introduced by Atari

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Atari 400/800/XL/XE

The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 as the Atari 400 and Atari 800 and manufactured until 1992. All of the machines in the family are technically similar and differ primarily in packaging. They are based on the MOS Technology 6502 CPU running at 1.79 MHz, and were the first home computers designed with custom coprocessor chips. This architecture enabled graphics and sound more advanced than contemporary machines, and gaming was a major draw. First-person space combat simulator Star Raiders is considered the platform's killer app. The systems launched with plug-and-play peripherals using the Atari SIO serial bus, an early analog of USB.

The Atari 400 and 800 differ primarily in packaging. The 400 has a pressure-sensitive, spillproof membrane keyboard and initially shipped with 8 KB of RAM. The 800 has a conventional keyboard, a second (rarely used) cartridge slot, and slots that allow easy RAM upgrades to 48K. Both models were replaced by the XL series in 1983, then–after the company was sold and reestablished as Atari Corporation–the XE models in 1985. The XL and XE are lighter in construction, have two joystick ports instead of four, and Atari BASIC is built-in. The 130XE has 128 KB of bank-switched RAM.

According to Atari, four million owners of Atari's home computer and 5200 games machines existed in 1984 ("Atari expect the new Lucasfilm software to stimulate sales of future games machines while tapping an existing market of 4 million owners of Atari's home computer and 5200 games machines", Business Week May 21, 1984). According to Jeremy Reimer, two million Atari 8-bit computers were sold during its major production run between late 1979 and mid-1985. They were sold through dedicated computer retailers and department stores, such as Sears, using an in-store demo to attract customers. The primary competition in the worldwide market came when the Commodore 64, with similar graphics performance, was introduced in 1982. In 1992, Atari Corporation officially dropped all remaining support for the 8-bit line.

The "Atari 8-bit family" label was not contemporaneous. Atari, Inc., used the term "Atari 800 home computer system", often combining the model names into "Atari 400/800" or simply "Atari home computers".


Design of the 8-bit series of machines started at Atari as soon as the Atari Video Computer System was released in late 1977. While designing the VCS in 1976, the engineering team from Atari Grass Valley Research Center (originally Cyan Engineering) felt the system would have a three-year lifespan before becoming obsolete. They started blue sky designs for a new console that would be ready to replace it around 1979.

What they ended up with was essentially a greatly updated version of the VCS, fixing its major limitations but sharing a similar design philosophy. The newer design would be faster and with better graphics and sound hardware. Work on the chips for the new system continued throughout 1978 and focused on much-improved video coprocessor known as the CTIA (the VCS version was the TIA).

During the early development period, the home computer era began in earnest with the TRS-80, Commodore PET, and Apple II—what Byte magazine dubbed the "1977 Trinity." Nolan Bushnell sold Atari to Warner Communications for $28 million in 1976 in order to raise funds for the launch of the VCS. Warner had recently hired Ray Kassar to act as the CEO of the company. Kassar felt the chipset should be used in a home computer to challenge Apple. To adapt the machine to this role, it needed to support character graphics, some form of expansion for peripherals, and run the then-universal BASIC programming language.

The VCS lacks bitmap graphics and a character generator. All on-screen graphics are created using sprites and a simple background generated by data loaded by the CPU into single-scan-line video registers. The then-Atari engineer Jay Miner developed the multimedia-chips for the Atari 8-bit family. The CTIA display chip was designed on the same principle, including sprites and background (playfield) graphics, but to reduce load on the main CPU, the task of loading video registers/buffers on the fly was delegated to a newly-designed dedicated graphics microprocessor, the Alphanumeric Television Interface Controller, or ANTIC. The CTIA and ANTIC work together to produce a complete display, with ANTIC fetching and buffering per-scan-line video data from the video frame-buffer and sprite memory in RAM, plus character set memory (for character modes), and feeding these data on-the-fly to the CTIA, which processes the sprite and playfield data in the light of its own color, sprite and graphics handling registers to produce the final color video output.

The resulting system was far in advance of anything then available on the market. Commodore was developing their own video driver in-house at the time, but Chuck Peddle, lead designer of the 6502 used in the VCS and the new machines, saw the Atari work during a visit to Grass Valley. He realized the Commodore design would not be competitive but he was under a strict non-disclosure agreement with Atari, and was unable to tell anyone at Commodore to give up on their own design. Peddle later commented that "the thing that Jay did, just kicked everybody's butt."


"Colleen" (named after two Atari secretaries). Atari would market Colleen as a computer and Candy as a game machine or hybrid game console. Colleen included user-accessible expansion slots for RAM and ROM, two 8 KB ROM cartridge slots, RF and monitor output (including two pins for separate luma and chroma, allowing a complete S-Video output) and a full keyboard. Candy was initially designed as a game console, lacking a keyboard and input/output ports, although an external keyboard was planned that could be plugged into joystick ports 3 and 4. At the time, plans called for both to have a separate audio port supporting cassette tapes as a storage medium.

A goal for the new systems was user-friendliness. One executive stated, "Does the end user care about the architecture of the machine? The answer is no. 'What will it do for me?' That's his major concern. ... why try to scare the consumer off by making it so he or she has to have a double E or be a computer programmer to utilize the full capabilities of a personal computer?" Cartridges would for example, Atari believed, make the computers easier to use. To minimize handling of bare circuit boards or chips, as was common with other systems of that period, the computers were designed with enclosed modules for memory, ROM cartridges, with keyed connectors to prevent them being plugged into the wrong slot. The operating system boots automatically, loading drivers from devices on the serial bus (SIO). The DOS system for managing floppy storage was menu-driven. When no software is loaded, rather than leaving the user at a blank screen or machine language monitor, the OS goes to the "Memo Pad" mode allowing the user to type using the built-in full-screen editor.

As the design process for the new machines continued, there were questions about what the Candy should be. There was a running argument about whether the keyboard would be external or built in. By the summer of 1978, education had become a focus for the new systems. While the Colleen design was largely complete by May 1978, it was not until early 1979 that the decision was made that Candy would also be a complete computer, but one intended for children. As such, it would feature a new keyboard designed to be resistant to liquid spills.

Atari intended to port Microsoft BASIC to the machine as an 8 KB ROM cartridge. However, the existing 6502 version from Microsoft was around 7,900 bytes, leaving no room for extensions for graphics and sound. The company contracted with local consulting firm Shepardson Microsystems to complete the port. They recommended writing a new version from scratch, resulting in Atari BASIC.