Atari 8-bit family

Atari 8-bit family

The Atari 800, featuring a full keyboard and dual-width cartridge slot cover.
Manufacturer Atari, Inc. (1979–1984)
Atari Corp. (1984–1992)
Type Home computer
Release date November 1979 (1979-11)
Introductory price US$ 495 (400, 1979)
Discontinued January 1992 (1992-01)
Units sold 4 million
Operating system Atari 8-bit OS
CPU MOS Technology 6502B
@ 1.79 MHz (NTSC version)
@ 1.77 MHz (PAL version)
Graphics 384 pixels per TV line, 256 colors, 8× sprites, raster interrupts
Sound oscillators with noise mixing,
or 2× AM digital
Connectivity 2× (or 4×) Joystick, 1× Atari SIO, 1× (or 0×) PBI, 1× (or 0×) Composite Monitor,1× (or 2×) ROM cartridge
Successor Atari ST
Related articles Atari 5200

The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 [1] and manufactured until 1992. All of the machines in the family are similar and differ primarily in packaging. They are based on the MOS Technology 6502 CPU running at 1.79 MHz,[lower-alpha 1], and were the first home computers designed with custom co-processor chips. This architecture allowed the Atari designs to offer graphics and sound capabilities that were more advanced than contemporary machines like the Apple II or Commodore PET, and gaming on the platform was a major draw; Star Raiders is widely considered the platform's killer app.

The original Atari 400 and 800 models were released with a series of plug-n-play peripherals that used Atari's "SIO" serial bus system, an early analog of the modern USB.[2][lower-alpha 2] To meet stringent FCC requirements, the early machines were completely enclosed in a solid cast aluminum block, which made them physically robust but expensive to produce. Over the following decade, the original models were replaced by the XL and XE series which had the same basic logical design, but were of much lighter construction and less expensive to build.

The Atari 8-bit computer line sold two million units during its major production run between late 1979 and mid-1985.[3] They were not only sold through dedicated computer retailers, but department stores such as Sears, using an in-store demo to attract customers.[4] The primary competition in the worldwide market was, starting in 1982, the Commodore 64. This was the first computer to offer similar graphics performance, and went on to be the best selling computer of the 8-bit era. Atari also found a strong market in Eastern Europe and had something of a renaissance in the early 1990s as these countries joined a uniting Europe.

On January 1, 1992, Atari corp. officially dropped all remaining support of the 8-bit line.[5]



Design of the 8-bit series of machines started at Atari as soon as the Atari 2600 games console was released in late 1977. While designing the 2600 in 1976, the engineering team from Atari Grass Valley Research Center (originally "Cyan Engineering")[6] felt that the 2600 would have about 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.[7]

What they ended up with was essentially a greatly updated version of the 2600, fixing its more obvious limitations but sharing a similar overall design philosophy.[7] The newer design would be faster than the 2600, have better graphics, and would include much better sound hardware. Work on the chips for the new system continued throughout 1978 and focused on much-improved video hardware known as the Alphanumeric Television Interface Controller, or ANTIC and the Color Television Interface Adaptor, or CTIA.[8]

During this gestation the home computer era began in earnest in the form of the TRS-80, Commodore PET, and Apple II family—what Byte Magazine would dub the "1977 Trinity".[9] Warner Communications had purchased Atari from Nolan Bushnell for $28 million in 1976 in order to fund the launch of the 2600. Atari had recently sent Ray Kassar to act as the CEO of the company. Kassar felt the chipset should be used in a home computer to challenge Apple.[2] In order to adapt the machine to this role, it would need to support character graphics, include some form of expansion for peripherals, and run the then-universal BASIC programming language.[7]

The need for character graphics led to the introduction of the ANTIC, a co-processor built to generate conventional bitmap graphics and characters providing a number of different modes with varying color support and resolution. Like the earlier TIA of the 2600, the CTIA was designed to produce Player-Missile graphics (sprites) and expanded to provide the color for the ANTIC's playfield graphics. ANTIC and CTIA work in concert to produce the complete display.[10]

The early machines: 400 and 800

Atari 400 (1979). Featuring a membrane keyboard and single-width cartridge slot cover.
The Atari 800 with the top flap removed, showing the expansion cards and two cartridge slots.
The Atari 800 used large expansion cards for the RAM, ROM and processor. Most Atari 800s shipped with three of these 16KB RAM cards, for a total of 48KB.

Management identified two sweet spots for the new computers: a low-end version known as Candy, and a higher-end machine known as Colleen (named after two attractive Atari secretaries).[11] The primary difference between the two models was marketing; Atari marketed Colleen as a computer, and Candy as a game machine or hybrid game console. Colleen includes user-accessible expansion slots for RAM and ROM, two 8 KB cartridge slots, RF and monitor output (including two pins for separate luma and chroma) and a full keyboard. Candy was initially packaged as a games 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.[12]

At the time, the Federal Communications Commission (FCC) mandated that signal leakage protection in the television frequency range had to be extremely effective for consumer devices. Other manufacturers had avoided this problem by leaving out those components, as in the Apple II,[13] or, using composite monitors like the PET or TRS-80.[lower-alpha 3] One of their existing sales partners, Sears, demanded that the machines meet the FCC's requirements so they could be sold off-the-shelf.[2]

To meet this requirement while including internal TV circuitry, they needed to be heavily shielded. Both machines were built around very strong cast aluminum shields forming a partial Faraday cage, with the various components screwed down onto this internal framework. This had the advantage of producing an extremely sturdy computer, although at the disadvantage of added manufacturing expense and complexity. The FCC ruling also made it difficult to have any sizable holes in the case, which eliminated expansion slots or cards that communicated with the outside world via their own connectors. Instead, Atari designed the Serial Input/Output (SIO) computer bus, a daisy-chainable system that allowed multiple, auto-configuring devices to connect to the computer through a single shielded connector. The internal slots were reserved for ROM and RAM modules; they did not have the control lines necessary for a fully functional expansion card.[2]

An overarching 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.[14] To minimize handling of bare circuit boards or chips as common with upgrades or even initial set up of other systems of that period, the computers were designed with enclosed modules for memory, ROM cartridges, and keyed connectors. The system does not require the user enter commands to boot the system; the operating system boots automatically, loading drivers from devices on the serial bus (SIO). The DOS system for managing floppy storage is menu driven. When no software was 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 (a la the TV Typewriter) using the built-in full screen editor.[10]

As the design process for the new machines continued, there was ongoing questions about what the Candy would be - the basic design required a keyboard in many situations and the argument continued on whether it would be external or built in.[15] By the summer of 1978, education had become a focus for the new systems. While the Colleen design is largely complete by May 1978, it is not until early 1979 that the decision was made that Candy would be a complete computer, but one aimed at children. As such, it would feature a new keyboard designed to be proof from minor liquid spills.[16]

Atari originally intended to port Microsoft BASIC to the machine, as had most other vendors, intending to supply it on an 8 KB ROM cartridge. However the existing 6502 version from Microsoft was 12 KB, and Atari's attempts to pare it down to 8 KB failed. The company contracted with a local consulting firm, Shepardson Microsystems which recommended writing its own version from scratch, resulting in Atari BASIC.[17]

After announcing the intent to enter the home computer market in December 1978,[18] the machines were first presented at the Winter CES in January 1979 as the 400 and 800.[19] The computers shipped in November 1979, much closer to the original design date. The names originally referred to the amount of memory, 4 KB RAM in the 400 and 8 KB in the 800. However, by the time they were released the prices on RAM had started to fall, so the machines were instead both released with 8 KB. As memory prices continued to fall Atari eventually supplied the 800 fully expanded to 48 KB, using up all the slots. Overheating problems with the memory modules eventually led Atari to remove the module's casings, leaving them as "bare" boards. Later, the expansion cover was held down with screws instead of the easier to open plastic latches.[20]

Both computers have four joystick ports, but only a few games such as M.U.L.E. use them all to permit four simultaneous players. With paddles, eight players could play Super Breakout.[21] The Atari 400, despite its membrane keyboard and single internal ROM cartridge slot, outsold the full keyboard and RAM expandable Atari 800 by a 2-to-1 margin.[3] Atari intended cartridges in the 800's right slot to supplement those in the left, but only a few right-slot cartridges were produced (just one by March 1983), and later computers omitted the slot.[22][21]


Despite planning an extensive advertising campaign for 1980,[14] Atari found competing with microcomputers from market leaders Commodore, Apple, and Tandy difficult. By mid-1981 it had reportedly lost $10 million on sales of $10 million.[23] The 400 and 800 were complex and expensive machines to build, consisting of multiple circuit boards mostly enclosed by massive die-cast aluminum shielding. Additionally, the machine was designed to add RAM only through cards, though it soon shipped fully expanded right from the factory. Soldering that RAM to the motherboard would be much less expensive than the connectors and separate cards needed in the 800. At the same time the 400 did not compete technically with some of the newer machines appearing in the early 1980s, which generally came standard with much more RAM and an upgraded keyboard.

Through this period, the issue of television interference was turning into a major issue with the FCC. The Apple II had avoided the problem by placing the RF modulator in an external box and selling it through a 3rd party. This avoided the problem that the FCC wanted to test the system as a whole, but a 3rd party product could not be considered part of the Apple II. Texas Instruments (TI) provided a better solution; in July 1977 they showed Atari engineers an inexpensive fibre optic connector that Joe Decuir proposed using as the connector for an RF modulator which could be considered completely separate from the base unit. His manager, Wade Tuma, shot down the idea saying "The FCC would never let us get away with that stunt." Unknown to Atari, TI was designing its own computer, the TI-99/4, and decided to use Decuir's idea. As Tuma had predicted, the FCC rejected the design and this led to delays in its release. TI was in the home district of the current speaker of the house, Jim Wright, and the issue blew up into a minor political battle.[24]

The FCC responded by creating two "classes" of devices under the original standard, Class A for industrial equipment, and Class B for consumer devices. At first it appeared this would solve the problems, but in 1981, the FCC made the issue even worse by demanding all computer devices be tested at their labs, rather than the manufacturer labs as had been the case in the past. Additionally, they stated that any add-on devices also had to be tested, and defined this in such a way that it included plug-in peripherals. At this point a number of companies, notably Atari, began to loudly complain that the FCC was in danger of putting them out of business. When the rules came into effect Radio Shack cancelled production of their TRS-80 Model I and substituted the shielded all-in-one Model III.[25]

The solution ultimately came due to a previous decision by the FCC that handheld calculators could meet Class B requirements with a simple self-verification process, as opposed to a complete testing procedure. They claimed that "Obviously size, power requirements and capability of the device will determine whether it is subject to certification or not."[26] As the battle continued, manufacturers increasingly claimed their devices fell into this second category, and the rules were eventually rendered toothless. At this point Atari, and other companies, were able to make machines with much less shielding and less expensive self-administered testing.

In 1982 Atari started the Sweet 8 (or "Liz NY") and Sweet 16 projects to take advantage of these changes. The result was an upgraded set of machines otherwise similar to the 400 and 800, but much easier to build and less costly to produce. Whereas the previous machines had individual circuit boards mounted inside and outside the internal shield, in the new design a single board supported all of the circuitry and the much thinner shielding was attached to it. This reduction in complexity was helped by improvements in chip making since the original machines were released, allowing a number of separate chips in the original systems to be condensed into one. Atari also ordered a custom version of the 6502, initially labeled "6502C" but eventually known as SALLY to differentiate it from a standard 6502C, which added a single pin that allowed four support chips to be removed. The SALLY was incorporated into late-production 400/800 machines, all subsequent XL/XE machines and the Atari 5200 and 7800 game systems.

Like the earlier machines, the Sweet 8/16 was intended to be released in two versions as the 1000 with 16 KB and the 1000X with 64 KB; RAM was still expensive enough to make this distinction worthwhile. In order to support expansion for high-end systems, similar to the card slots used in the Apple II or S-100 machines, the 1000 series also supported the Parallel Bus Interface (PBI), a single expansion slot on the back of the machine. An external chassis could be plugged into the PBI, supporting card slots for further expansion.

XL Series


Atari 1200XL

For reasons that are not clear in historical sources, the original Liz plans were dropped and only one machine using the new design was released. Announced at a New York City press conference on December 13, 1982,[27][28] the rechristened 1200XL was presented at the Winter CES on January 6–9, 1983[29] and shipped in March 1983.[30] Notable features were 64 KB of RAM, built-in self test, redesigned keyboard (featuring four function keys and a HELP key), and redesigned cable port layout.[22]

The 1200XL included a number of missing or poorly implemented features. The PBI expansion connector from the original 1000X design was left off, making the design rely entirely on the SIO port again. Frustrating this was the fact that the +12V pin in the SIO port was left unconnected; only +5V power was available which made a few devices stop working.[lower-alpha 4] An improved video circuit provided more chroma for a more colorful image, but the chroma line was not connected to the monitor port, the only place that could make use of it. Even the re-arrangement of the ports made some joysticks and cartridges difficult or impossible to use. Changes made to the operating system to support the new hardware also resulted in compatibility problems with some older software that did not follow published guidelines. Considered as a whole, the differences between the 1200 and earlier machines was minor, or even retrograde.

The machine was released at $899.[29] This was $100 less than the announced price of the 800 at its release in 1979, but by this time the 800 was available at much lower price points. The press warned that the 1200XL was too expensive. Compute! stated in an early 1983 editorial:[31]

We're hard pressed to figure out what Atari is up to ... We're concerned about the emperor's new clothes because the actual features of the XL seem off base when compared to the competition. For example, the Atari 800[, less than $700] ... we're concerned that the 1200XL has been introduced to fill a nonexistent hole in Atari's product line.

John Anderson, writing in Creative Computing's Outpost: Atari column echoed these comments:[32]

If it had been announced at $499 instead of $899, it would have been a welcome addition to the Atari computer line... The 1200 has met with nearly universal insouciance in the microcomputer community, and for good reason. It has an extra 16K in a designer case, without a right cartridge slot, expansion slots, or a third and fourth controller jack. It has no standard parallel or RS-232 ports. Only substantive price cuts will help its image in any tangible way.

Bill Wilkinson, co-founder of Optimized Systems Software and columnist for Compute!, in May 1983 criticized the computer's features and price:[33]

So how do I rate the 1200XL in overall features and performance? Quite honestly, it depends entirely on what the price of the machine is. At anything under $450, it's a terrific bargain ... it should be able to sell for half the cost of the 800. However, the indications are that the price of the 800 will be dropped and that the 1200 will cost more than the 800. If so, buy an 800 quick!

There is an often-repeated story, perhaps apocryphal, that 800 sales rose after the release of the 1200XL, as people bought them before they disappeared.[34] The machine was discontinued in June 1983. There was no PAL version of the 1200XL.

Newer XL machines

Atari 600XL. This machine featured a slightly shallower case than the 800XL.

By this point in time Atari was involved in what would soon develop into a full-blown price war when Jack Tramiel of Commodore International was attempting to undercut his old enemy Texas Instruments. TI had undercut Commodore's calculator business only a few years earlier, almost driving him from the market. To ensure this would not happen again, Tramiel purchased MOS Technology to ensure his supply line, and this time he could turn the tables. The result was a breathtaking decline in home computer prices, reducing them as much as eight times over a period of a few months.

In May 1981 the Atari 800's price was $1,050[35] but by July 1983 was $165.[36] Although Atari had never been a deliberate target of Tramiel's wrath, they, along with the rest of the market, were dragged into the price war in order to maintain market share. The timing was particularly bad for Atari; the 1200XL was a flop, and the earlier machines were too expensive to produce to be able to compete at the rapidly falling price points. The solution was to replace the 1200XL with a machine that users would again trust, while at the same time lowering the production costs to the point where they could compete with Commodore.

To do this, Atari engineers were able to add a number of new IC's to take over the functions of many of those remaining in the 1200XL. This resulted in an even simpler main PCB design, and slightly smaller cases to house it. A new lineup was announced at the 1983 Summer CES, closely following the original Liz/Sweet concepts.The 600XL was essentially the Liz NY model, and the spiritual replacement for the 400, while the 800XL would replace both the 800 and 1200XL. The machines looked similar to the 1200XL, but were smaller back to front, the 600 being somewhat smaller as it lacked one row of memory chips on the PCB. The high-end 1400XL and 1450XLD added a built-in 300 baud modem and a voice synthesizer, and the 1450XLD also included a built-in double-sided floppy disk drive in an enlarged case, with a slot for a second drive. The machines had Atari BASIC built into the ROM of the computer and the PBI at the back that allowed external expansion.

An Atari 800XL
The main circuit board of an Atari 800XL

By this point, in early 1983, the price war rapidly drove prices downward. Atari, attempting to beat this downward pressure, took the opportunity to move production of the new machines to the far east, where they could be produced at even lower cost. However, the production move ran into unexpected delays. Originally intended to replace the 1200XL in mid-83, the machines did not arrive until late the year. Although the 600/800 were well positioned in terms of price and features, during the critical Christmas season they were available only in small numbers while the Commodore 64 was widely available. Although the 800XL would ultimately be the most popular computer sold by Atari, it was unable to defend Atari's marketshare, and the race to the bottom gutted their profits.[37] The 600XL and 800XL's prices in early 1984 were $50 higher than for the Commodore VIC-20 and 64,[38] and a rumor stated that the company planned to discontinue hardware and only sell software.[39] Combined with the simultaneous effects of the video game crash of 1983, Atari was soon losing millions of dollars a day. Their owners, Warner Communications, became desperate to sell off the division.

Through this process the 1400XL and the 1450XLD had their delivery dates pushed back, first by the priority given to the 600XL/800XL, and later by the 3600 System. In the end the 1400XL was canceled outright, and the 1450XLD so delayed that it would never ship. Other prototypes which never made it to market include the 1600XL, 1650XLD, and 1850XLD. The 1600XL was to have been a dual-processor model capable of running 6502 and 80186 code, while the 1650XLD was a similar machine in the 1450XLD case. These were canceled when James J. Morgan became CEO and wanted Atari to return to its video game roots.[40] The 1850XLD was to have been based on the custom chipset in the Amiga Lorraine[41] (later to become the Commodore Amiga).

Tramiel takeover, declining market

Although Commodore emerged intact from the computer price wars, fighting inside Commodore soon led to Jack Tramiel's ousting in January 1984. Looking to re-enter the market, he purchased the Atari consumer division in July 1984 from Warner for an extremely low price. When Jack Tramiel took over Atari the high-end XL models were canceled and the low-end XLs were redesigned into the XE series. Nearly all Atari's research, design and prototype projects were arbitrarily cancelled, often with the new management completely ignorant of the nature of the projects. This included the Amiga-based 1850XLD system and other existing 68000 prototypes while Tramiel focused on developing the 68000-based Atari ST system and bringing in ex-Commodore engineers to work on the ST line.

Atari sold about 700,000 computers in 1984, compared to Commodore's two million.[42] As his new company prepared to ship the Atari ST in 1985, Tramiel stated that sales of Atari 8-bit computers were "very, very slow".[43] They were never an important part of Atari's business compared to video games, and it is possible that the 8-bit line was never profitable for the company despite selling almost 1.5 million computers by early 1986.[23][39][36]

By that year the Atari software market was decreasing in size. Antic magazine stated in an editorial in May 1985 that it had received many letters complaining that software companies were ignoring the Atari market, and urged readers to contact the companies' leaders.[44] "The Atari 800 computer has been in existence since 1979. Six years is a pretty long time for a computer to last. Unfortunately, its age is starting to show", ANALOG Computing wrote in February 1986. The magazine stated that while its software library was comparable in size to that of other computers, "now—and even more so in the future—there is going to be less software being made for the Atari 8-bit computers", warning that 1985 only saw a "trickle" of major new titles and that 1986 "will be even leaner".[45]

Computer Gaming World that month stated "games don't come out for the Atari first anymore".[46] In April the magazine published a survey of 10 game publishers which found that they planned to release 19 Atari games in 1986, compared to 43 for Commodore 64, 48 for Apple II, 31 for IBM PC, 20 for Atari ST, and 24 for Amiga; only the Macintosh's 17 was fewer. Companies stated that one reason for not publishing for Atari was the unusually high amount of software piracy on the computer, partly caused by the Happy Drive.[47][48][49] The magazine warned later that year, "Is this the end for Atari 800 games? It certainly looks like it might be from where I write",[48] and in 1987 MicroProse explicitly denied rumors that it would release Gunship for the Atari, stating that the market was too small.[50]

Tramiel era: XE series

Atari 130XE
Atari XE Game System

Tramiel, originally from Poland, retained strong links with eastern Europe. When these countries began to remove themselves from the Warsaw Pact, capped by the fall of the Berlin Wall in 1989, he was able to use these relationships to open new business opportunities for the company. To address the need for a very low cost machine suitable for sales into these regions, where the economies were still post-communist and the exchange rates very high, Atari introduced the last machines in the 8-bit series to hit very low price points.

These were the 65XE and 130XE (XE stood for XL-Expanded). They were announced in 1985, at the same time as the initial models in the Atari ST series, and visually resembled the Atari ST. Originally intended to be called the 900XLF, the 65XE had 64 KB of RAM and was functionally equivalent to the 800XL minus the PBI connection. The 130XE had 128 KB of memory, accessible through bank-selection, and the Enhanced Cartridge Interface (ECI), which was electronically almost compatible with the Parallel Bus Interface (PBI), but physically smaller, since it was located next to the standard 400/800-compatible Cartridge Interface and provided only those signals that did not exist in the latter; ECI peripherals were expected to plug into both the standard Cartridge Interface and the ECI port. Later revisions of the 65XE contained the ECI port as well. The 130XE was aimed to appeal at the mass market.[51]

The 65XE was marketed as 800XE in Germany and Czechoslovakia, in order to ride on the popularity of the original 800XL in those markets. Being available on market from 1987, all 800XE units contained the ECI port.[52]

XE Game System

See also: Atari XEGS

By this time, Nintendo demonstrated that a market for a dedicated video game console existed, prompting Atari to re-enter the market. Instead of using their existing consoles, they released the XE Game System (XEGS) in 1987. The XE Game System is a repackaged 65XE and is compatible with almost all Atari 8-bit software and hardware as a result. The XE Game System was sold bundled with a detachable keyboard, a joystick and a light gun (XG-1), and two game cartridges (Bug Hunt and Flight Simulator II). Most of the games were older titles, such as Necromancer and Blue Max (both originally published by Synapse, not Atari), ported to cartridge format.

Production Timeline

Production timeline dates retrieved from Atari 8-Bit Computers F.A.Q.,[52] and Chronology of Personal Computers.[53]

End of support and legacy

On January 1, 1992, Atari corp. officially dropped all remaining support of the 8-bit family.[5]

In 2006 Atari veteran Curt Vendel, who designed the Atari Flashback for Atari, Inc. in 2004,[54] claimed that Atari released the 8-bit chipset into the public domain.[55]

Also, there is agreement in the community that Atari authorized the distribution of the Atari 800's ROM with the X-Former 2.5 emulator, which makes the ROM legally available today as freeware.[56][57]


The processor board for the Atari 800, showing the 6502, ANTIC and CTIA chips.

The Atari machines consist of a 6502 as the main processor, a combination of ANTIC and GTIA chips to provide graphics, and the POKEY chip to handle sound and serial input/output. These "support" chips are controlled via a series of registers that can be user-controlled via memory load/store instructions running on the 6502. For example, the GTIA uses a series of registers to select colors for the screen; these colors can be changed by inserting the correct values into its registers, which are mapped into "memory" that is visible to the 6502. Some parts of the system also use some of the machine's RAM as a buffer, notably the ANTIC's display buffer and its Display List (essentially a small program written in the chip's simple machine language that tells ANTIC how to interpret that data and turn it into a display), as well as GTIA's Player/Missile (sprite) information.

The custom hardware features enable the computers to perform many functions directly in hardware, such as smooth background scrolling, that would need to be done in software in most other computers. Graphics and sound demos were part of Atari's earliest developer information and used as marketing materials with computers running in-store demos.


ANTIC is a microprocessor which processes display instructions. A complete sequence of instructions is known as a Display List. Each instruction describes how a single "line" on the screen is to be displayed (specifying one of several character or graphics modes available), where it is displayed, if it contains interrupts, if fine scrolling is enabled or not, and optionally where to load data from memory (text or graphics information). Since each line can be programmed individually, this feature enables the programmer to create displays made up of mixed graphics and text, as well as different graphics modes on one screen without using CPU intervention. The Display List and the largely unrestricted access to memory enables the machine to quickly coarse or fine "scroll" the screen vertically or horizontally by means of a few memory writes.

ANTIC reads this Display List and the display data using DMA (Direct Memory Access), then translates the result into a pixel data stream representing the playfield text and graphics. This data stream then passes to GTIA which applies the playfield colors and incorporates the Player/Missile graphics (sprites) for final output to a TV or composite monitor. In the middle of this ANTIC also performs DMA to update GTIA's Player/Missile image data on each scan line. Once the Display List and DMA parameters are set the display is generated automatically without any direct CPU intervention.

Additionally, the character set is easily redirected by changing a register, allowing the user to create their own character sets with relative ease. Depending on the text mode used the character set can occur on any 1K or 512 byte page boundary in the 64K address space. Fast and efficient animation can be achieved by simply changing the register to point to different character sets. ANTIC includes additional register controls over character display that permit it to invert (flip upside down) the character matrix. A register control can also modify the state of reverse video characters which can be used to produce blinking text.


The Color Television Interface Adaptor[58] (CTIA) is the graphics chip used in early Atari 400/800 home computers. It is the successor to the TIA chip used in the Atari 2600. According to Joe Decuir, George McLeod designed the CTIA in 1977. The CTIA chip was replaced with the Graphic Television Interface Adaptor[58] (GTIA) in later revisions of the 400 and 800 and all other members of the Atari 8-bit family. GTIA, also designed by George McLeod, adds three new color interpretation modes for ANTIC's Playfield graphics that enables the display of more colors on the screen than previously available.[59]

The CTIA/GTIA receives Playfield graphics information from ANTIC and applies colors to the pixels from a 128 or 256 color palette depending on the color interpretation mode in effect. CTIA/GTIA also controls Player/Missile Graphics (aka sprites) functionality including collision detection between displayed objects (Players, Missiles, and ANTIC's Playfield), display priority control over objects, and color/luminance control of all displayed objects. CTIA/GTIA outputs separate digital luminance and chrominance signals, which are mixed to form an analogue composite video signal.

The CTIA/GTIA is responsible for reading the console keys Option, Select, Start, and operating the keyboard speaker in the Atari 400/800. In later computer models the audio output for the keyboard speaker is mixed with the audio out for transmission to the TV/video monitor. CTIA/GTIA is also responsible for reading the joystick triggers.

Certain 65XE and 800XE machines sold in Eastern Europe had a buggy GTIA chip, specifically those machines made in China in 1991.


The third custom support chip, named POKEY, is responsible for reading the keyboard, generating sound and serial communications (in conjunction with the PIA). It also provides timers, a random number generator (for generating acoustic noise as well as random numbers), and maskable interrupts. POKEY has four semi-independent audio channels, each with its own frequency, noise and volume control. Each 8-bit channel has its own audio control register which select the noise content and volume. For higher sound frequency resolution (quality), two of the audio channels can be combined for more accurate sound (frequency can be defined with 16-bit value instead of usual 8-bit). The name POKEY comes from the words "POtentiometer" and "KEYboard", which are two of the I/O devices that POKEY interfaces with (the potentiometer is the mechanism used by the paddle). The POKEY chip—as well as its dual- and quad-core versions—were used in several Atari coin-op arcade machines of the 80s, including Missile Command and Asteroids Deluxe, among others.[60]

Computer models



Atari 1020 four-color Plotter

During the lifetime of their eight-bit series, Atari released a large number of peripherals. These included:

Atari's peripherals used the proprietary Atari SIO port, which allowed them to be daisy chained together into a single string. A primary goal of the Atari computer design was user-friendliness which was assisted by the SIO bus. Since only one kind of connector plug is used for all devices the Atari computer was easy for novice users to expand. Atari SIO devices used an early form of plug-n-play. Peripherals on the bus have their own IDs, and can deliver downloadable drivers to the Atari computer during the boot process. However, the additional electronics in these "intelligent" peripherals made them cost more than the equivalent "dumb" devices used by other systems of that era.


Atari at first did not disclose technical information for its computers, except to software developers who agreed to keep it secret, possibly to increase its own software sales.[62] Cartridge software was so rare at first that InfoWorld joked in 1980 that Atari owners might have considered turning the slot "into a fancy ashtray". The magazine advised them to "clear out those cobwebs" for Atari's Star Raiders,[63] which became the platform's killer app, akin to VisiCalc for the Apple II in its ability to persuade customers to buy the computer.[64]

Chris Crawford and others at Atari eventually published detailed information in De Re Atari.[65] Because of graphics superior to that of the Apple II[66] and Atari's home-oriented marketing, games dominated its software library. A 1984 compendium of reviews used 198 pages for games compared to 167 for all others.[67]

Operating system


The Atari 8-bit computers came with an operating system built into the ROM. The Atari 400/800 had the following:

The XL/XE Atari 8-bit models all had OS revisions due to added hardware features and changes. But this created compatibility issues with some of the older software. Atari responded with the Translator Disk, a floppy disk which loaded the older 400/800 Rev. 'B' or Rev. 'A' OS into the XL/XE computers.

The XL/XE models that followed the 1200XL also came with the Atari BASIC ROM built in, which could be disabled at startup by holding down the silver OPTION key to the right of the keyboard; the earlier-manufactured 1200XL required an Atari BASIC cartridge for that functionality. Early models with built-in BASIC came with the notoriously buggy revision B. Later models used revision C.

Disk Operating System

Main article: Atari DOS

The standard Atari OS only contained very low-level routines for accessing floppy disk drives. An extra layer, a disk operating system, was required to assist in organizing file system-level disk access. This was known as Atari DOS, and like most home computer DOSes of the era, had to be booted from floppy disk at every power-on or reset. Unlike most DOSs, Atari DOS was entirely menu-driven.

Several third-party replacement DOSes were also available, sometimes quite advanced, such as SpartaDOS X.

Playfield graphics capabilities

Moiré pattern in 320 horizontal pixel graphics mode. The colors are artifacts of displaying hi-res pixels which are half the size of the NTSC color clock.

While the ANTIC chip allows a variety of different Playfield modes and widths, the original Atari Operating System included with the Atari 800/400 computers provides easy access to a limited subset of these graphics modes. These are exposed to users through Atari BASIC via the "GRAPHICS" command, and to some other languages, via similar system calls. Oddly, the modes not directly supported by the original OS and BASIC are modes most useful for games. The later version of the OS used in the Atari 8-bit XL/XE computers added support for most of these "missing" graphics modes.

ANTIC text modes support soft, redefineable character sets. ANTIC has four different methods of glyph rendering related to the text modes: Normal, Descenders, Single color character matrix, and Multiple colors per character matrix.

The ANTIC chip uses a Display List and other settings to create these modes. Any graphics mode in the default CTIA/GTIA color interpretation can be freely mixed without CPU intervention by changing instructions in the Display List.

The actual ANTIC screen geometry is not fixed. The hardware can be directed to display a narrow Playfield (128 color clocks/256 hi-res pixels wide), the normal width Playfield (160 color clocks/320 hi-res pixels wide), and a wide, overscan Playfield (192 color clocks/384 hi-res pixels wide) by setting a register value. While the Operating System's default height for creating graphics modes is 192 scan lines ANTIC can display vertical overscan up to 240 TV scan lines tall by creating a custom Display List.

The Display List capabilities provide horizontal and vertical coarse scrolling requiring minimal CPU direction. Furthermore, the ANTIC hardware supports horizontal and vertical fine scrolling—shifting the display of screen data incrementally by single pixels (color clocks) horizontally and single scan lines vertically.

The video display system was designed with careful consideration of the NTSC video timing for color output. The system CPU clock and video hardware are synchronized to one-half the NTSC clock frequency. Consequently, the pixel output of all display modes is based on the size of the NTSC color clock which is the minimum size needed to guarantee correct and consistent color regardless of the pixel location on the screen. The fundamental accuracy of the pixel color output allows horizontal fine scrolling without color "strobing"—unsightly hue changes in pixels based on horizontal position caused when signal timing does not provide the TV/monitor hardware adequate time to reach the correct color.

Character modes

ANTIC Text Mode OS mode Characters (or Bytes) Per Mode Line TV Scan Lines per Mode Line Colors Colors per Character Matrix Characters in Font Matrix Pixel Size (Color Clocks x Scan Lines) Matrix Map (Color Clocks x Scan Lines) Matrix Map (Pixels x Pixels ) Notes
2 0 32/40/48 8 1.5 1 128 1/2 x 1 4 x 8 8 x 8 High-res pixels. High bit of character displays the character data in inverse (values $80 to $FF)
3 N/A 32/40/48 10 1.5 1 128 1/2 x 1 4 x 8/10 8 x 8 High-res pixels. Lowercase characters are displayed 2 scan lines lower allowing descenders.
4 12 (XL OS) 32/40/48 8 5 4 128 1 x 1 4 x 8 4 x 8 Two bits per pixel allowing 4 colors inside one character matrix. When the high bit of the character is set a fifth color replaces one of the other four.
5 13 (XL OS) 32/40/48 16 5 4 128 1 x 2 4 x 16 4 x 8 Color same as above Antic Mode 4. Characters are twice as tall.
6 1 16/20/24 8 5 1 64 1 x 1 8 x 8 8 x 8 One color per character matrix. The two high bits of each character value specify the color of the character allowing a choice of four colors.
7 2 16/20/24 16 5 1 64 1 x 2 8 x 16 8 x 8 Color same as above Antic Mode 6. Characters are twice as tall.

Map modes

ANTIC Map Mode OS Mode Pixels Per Mode Line (narrow/normal/wide) TV Scan Lines per Mode Line Bytes per Mode Line (narrow/normal/wide) Colors Color Clocks per Pixel
8 3 32/40/48 8 8/10/12 4 4
9 4 64/80/96 4 8/10/12 2 2
A 5 64/80/96 4 16/20/24 4 2
B 6 128/160/192 2 16/20/24 2 1
C 14 (XL OS) 128/160/192 1 16/20/24 2 1
D 7 128/160/192 2 32/40/48 4 1
E 15 (XL OS) 128/160/192 1 32/40/48 4 1
F 8 256/320/384 1 32/40/48 1.5 1/2

GTIA modes

GTIA modes are Antic Mode F displays with an alternate color interpretation option enabled via a GTIA register. The full color expression of these GTIA modes can be engaged in Antic text modes 2 and 3, though these will also requires a custom character set to achieve practical use of the colors.

ANTIC Map Mode OS Mode Pixels Per Mode Line (narrow/normal/wide) TV Scan Lines per Mode Line Bytes per Mode Line (narrow/normal/wide) Colors Color Clocks per Pixel Notes
F 9 64/80/96 1 32/40/48 16* 2 16 shades of the background color.
F 10 64/80/96 1 32/40/48 9 2 uses all 9 playfield and player/missile color registers.
F 11 64/80/96 1 32/40/48 16* 2 15 color hues all in the same luminance specified by the background color register, though the background color is black.


Kilobaud Microcomputing wrote in 1980 that the Atari 800 "looks deceptively like a video game machine, [but had] the strongest and tightest chassis I have seen since Raquel Welch. It weighs about ten pounds ... The large amount of engineering and design in the physical part of the system is evident". The reviewer also praised the documentation as "show[ing] the way manuals should be done", and the "excellent 'feel'" of the keyboard.[68] InfoWorld favorably reviewed the computer's performance, graphics, and ROM cartridges, but disliked the documentation and cautioned that the unusual right shift key location might make the computer "unsuitable for serious word processing". Noting that the amount of software and hardware available for the computer "is no match for that of the Apple II or the TRS-80", the magazine concluded that the 800 "is an impressive machine that has not yet reached its full computing potential".[35]

See also


  1. Computers that used analog televisions as their primary output device, including the vast majority of designs in the home computer era, used odd clock speeds to match the precise timing of the television signal. Due to differences between the NTSC and PAL television systems, European computers often ran slightly slower than North American versions
  2. One of the 8-bit's engineers, Joe Decuir, would later work on the USB system while working at Microsoft, and is one of the contributors to the original USB patents.
  3. The TRS-80 did use a slightly modified black and white television as a monitor. It was notorious for causing interference, and production was cancelled when the more stringent FCC requirements came into effect on January 1, 1981.
  4. The +12V was typically used to power RS-232 devices, which now required an external power source.


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External links


Technical information

Software, games, music, demos

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