Atari 8-bit family
The Atari 8-bit family is a series of 8-bit home computers introduced by Atari, Inc. in 1979 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 co-processor chips. This architecture enabled graphics and sound capabilities more advanced than most contemporary machines, and gaming on the platform was a major draw. The first-person space combat simulator Star Raiders is considered the platform's killer app. The systems launched with a series of plug and play peripherals that used the Atari SIO serial bus system, an early analog of USB.
The Atari 800, with a full keyboard and dual-width cartridge slot cover
|Manufacturer||Atari, Inc. (1979–1984)|
Atari Corporation (1984–1992)
|Release date||November 1979|
|Introductory price||Atari 400: US$550 (equivalent to $1,899 in 2018)|
Atari 800: US$1,000 (equivalent to $3,452 in 2018)
|Units sold||4 million|
|Operating system||Custom OS|
Atari DOS (optional)
|CPU||MOS Technology 6502B|
@ 1.79 MHz (NTSC)
@ 1.77 MHz (PAL)
|Graphics||384 pixels per TV line, 256 colors, 8 × sprites, raster interrupts|
|Sound||4 × oscillators with noise mixing|
or 2 × AM digital
|Connectivity||2 or 4 × Atari joystick port|
1 × Atari SIO
0-1 × PBI
0-1 × Composite monitor
1-2 × ROM cartridge
|Related articles||Atari 5200|
To meet stringent FCC requirements, much of the circuitry of the original machines is enclosed in a cast aluminum block, which made them physically robust but expensive to produce. The 400 and 800 were replaced by the XL series in 1983, then the XE models in 1985. The XL and XE are lighter in construction and less expensive to build, while also having Atari BASIC built-in and reducing the number of joystick ports from 4 to 2. The 130XE, released in 1985, increased the memory to 128K of bank-switched RAM.
The Atari 8-bit computer line sold two million units during its major production run between late 1979 and mid-1985. They were not only sold through dedicated computer retailers, but department stores such as Sears, using an in-store demo to attract customers. The primary competition in the worldwide market came several years later when the Commodore 64, the first computer to offer similar graphics performance, was introduced in 1982. 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.
In 1992, Atari Corporation officially dropped all remaining support of the 8-bit line.
The "Atari 8-bit family" label was not contemporaneous. Atari, Inc., used the term "Atari 800 [or 400] home computer system," often combining the system 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 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") 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.
What they ended up with was essentially a greatly updated version of the 2600, fixing its major limitations but sharing a similar design philosophy. The newer design would be faster than the 2600 with better graphics and sound hardware. Work on the chips for the new system continued throughout 1978 and focused on much-improved video hardware known as the CTIA (the 2600 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 2600. Warner 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. 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 2600 lacks bitmap graphics and a character generator. All on-screen graphics are created using Player-Missile graphics (sprites) and a simple background using fixed patterns. The CTIA was designed on the same model, and likewise mainly used sprites for drawing. Instead of expanding the CTIA to handle these tasks, the designers introduced an entirely new chip for this purpose, the Alphanumeric Television Interface Controller, or ANTIC. The CTIA and ANTIC work together to produce a complete display, with the CTIA in charge of sprites and producing color video output, and the ANTIC in charge of bitmap (or "playfield" in Atari terms) and character graphics.
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 Atari secretaries). 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 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 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.
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 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.
As the design process for the new machines continued, there were ongoing questions about what the Candy should be - the basic design required a keyboard in many situations and 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 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 around 7,900 bytes, leaving no room for extensions for graphics and sound. The company contracted with a local consulting firm, Shepardson Microsystems, to complete the port. They recommended writing a new version from scratch, resulting in Atari BASIC.
At the time the machines were being designed, the Federal Communications Commission (FCC) mandated that consumer devices had to have extremely low signal leakage in the television frequency range. A device known as an RF modulator is normally used for television output, and these are difficult to shield to the levels being mandated by the FCC. Other manufacturers had avoided this problem using composite monitors on computers such as the PET or TRS-80.
Apple solved the problem by leaving those components out of the Apple II, and instead contracted M&R Enterprises to sell them under the name "Sup'R'Mod". The FCC required the entire device generating the signals to be tested as a whole, but as the RF modulator was sold by a 3rd party it was not considered to be part of the Apple II and could pass testing on its own. One of Atari's existing sales partners, Sears, did not consider such a solution to be suitable for off-the-shelf sales, so Atari could not use Apple's solution and the machine would have to meet the new specifications with a built-in RF modulator.
In a July 1977 visit with the engineering staff, a Texas Instruments (TI) salesman presented a new possibility in the form of an inexpensive fibre optic cable with built-in transceivers. During the meeting, Joe Decuir proposed using this in a similar fashion to Apple's solution by placing an RF modulator on one end, thereby completely isolating any electrical signals so that the computer itself would have no RF components. His manager, Wade Tuma, later 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 that machine's 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.
To meet the off-the-shelf requirement while including internal TV circuitry, the machines needed to be heavily shielded. Both 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, nor room to route a cable outside the case to communicate with external devices.
After announcing the intent to enter the home computer market in December 1978, the machines were first presented at the Winter CES in January 1979 as the 400 and 800.
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. By the time they were released, RAM prices had started to fall, so the machines were instead both released with 8 KB, using 4kx1 DRAMs. Further drops in memory prices during 1980 led to both machines shipping with completely maxed-out RAM; 16k and 48k respectively, using 16kx1 DRAMs. The user-installable RAM modules in the 800 initially had plastic casings but this proved to have overheating issues especially since the triple-voltage DRAM used at this time naturally tended to run hot, so the casings were removed. Later, the expansion cover was held down with screws instead of the easier to open plastic latches.
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. Paddle controllers were wired in pairs, and eight players could play Super Breakout. 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. 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 machines in the family omitted the slot.
Creative Computing mentioned the Atari machines in an April 1979 overview of the CES show. Calling Atari "the videogame people", it went on to state they came with "some fantastic educational, entertainment and home applications software." In an August 1979 interview Atari's Peter Rosenthal suggested that demand might be low until the 1980-81 time frame, when he predicted about one million home computers being sold. The April 1980 issue compared the machines with the Commodore PET, focused mostly on the BASIC dialects.
Ted Nelson reviewed the computer in the magazine in June 1980, calling it "an extraordinary graphics box". Describing his and a friend's "shouting and cheering and clapping" during a demo of Star Raiders, Nelson wrote that he was so impressed that "I've been in computer graphics for twenty years, and I lay awake night after night trying to understand how the Atari machine did what it did". He described the machine as "something else" before criticizing the company for a lack of developer documentation. Nelson concluded by stating "The Atari is like the human body - a terrific machine, but (a) they won't give you access to the documentation, and (b) I'd sure like to meet the guy that designed it."
Kilobaud Microcomputing wrote in September 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.
InfoWorld favorably reviewed the 800'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".
Despite planning an extensive advertising campaign for 1980, 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 $10-13 million from more than 50,000 computers.
In 1982, Atari started the Sweet 8 (or "Liz NY") and Sweet 16 projects to create an upgraded set of machines that were much easier to build and less costly to produce. Atari also ordered a custom version of the 6502, initially labelled "6502C," but eventually known as SALLY to differentiate it from a standard 6502C. SALLY was incorporated into late-production 400/800 machines, all subsequent XL/XE machines, and the 5200 and 7800 consoles.
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. 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.
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, the rechristened 1200XL was presented at the Winter CES on January 6–9, 1983 and shipped in March 1983. 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.
The 1200XL omitted several features, or they were poorly implemented. The PBI expansion connector from the original 1000X design was left off, making the design rely entirely on the SIO port again. The +12V pin in the SIO port was left unconnected; only +5V power was available which made a few devices stop working. 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.
Announced with a $1000 price, the 1200XL was released at $899. 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. Considered as a whole, the differences between the 1200 and earlier machines was minor, or even retrograde.
The press warned that the 1200XL was too expensive. Compute! stated in an early 1983 editorial:
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:
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, author of Atari BASIC, co-founder of Optimized Systems Software, and columnist for Compute!, in May 1983 criticized the computer's features and price:
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. By mid-1983 the computer was sold for $600-700. It was discontinued in June 1983. There was no PAL version of the 1200XL.
Newer XL machines
By this point in time Atari was involved in what would soon develop into a full-blown price war. Several years earlier, Commodore was a major calculator vendor, selling designs based on a Texas Instruments (TI) chipset. TI decided to enter the market themselves and suddenly raised the prices to other vendors, nearly putting Commodore out of business.
To ensure this would not happen again, Jack Tramiel of Commodore International purchased MOS Technology to ensure his supply of the 6502 for his computers. When TI introduced the TI-99, Tramiel turned the tables on them by pricing his machines below theirs. A price war ensued, causing a dramatic 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, but by mid-1983 it was $165 and the 400 was under $150. Although Atari had never been a deliberate target of Tramiel's wrath, the Commodore/TI price war affected the entire market. 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.
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 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.
Atari had difficulty in transitioning manufacturing to Asia after closing its US factory. Originally intended to replace the 1200XL in mid-1983, the new models did not arrive until late that year. Although the 600XL/800XL 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. Brian Moriarty stated in ANALOG Computing that Atari "fail[ed] to keep up with Christmas orders for the 600 and 800XLs", reporting that as of late November 1983 the 800XL had not appeared in Massachusetts stores while 600XL "quantities are so limited that it's almost impossible to obtain".
Although the 800XL would ultimately be the most popular computer sold by Atari, the company was unable to defend its market share, and the ongoing race to the bottom reduced Atari's profits. Prices continued to erode; by November 1983 one toy store chain sold the 800XL for $149.97, $10 above the wholesale price. After losing $563 million in the first nine months of the year, Atari that month announced that prices would rise in January, stating that it "has no intention of participating in these suicidal price wars". The 600XL and 800XL's prices in early 1984 were $50 higher than for the Commodore VIC-20 and 64, and a rumor stated that the company planned to discontinue hardware and only sell software. 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.
The 1400XL and the 1450XLD had their delivery dates pushed back, and in the end, the 1400XL was cancelled 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. The 1850XLD was to have been based on the custom chipset in the Amiga Lorraine (later to become the Commodore Amiga).
ANALOG Computing, writing about the 600XL in January 1984, stated that "the Commodore 64 and Tandy CoCo look like toys by comparison." The magazine approved of its not using the 1200XL's keyboard layout, and predicted that the XL's parallel bus "actually makes the 600 more expandable than a 400 or 800". While disapproving of the use of an operating system closer to the 1200XL's than the 400 and 800's, and the "inadequate and frankly disappointing" documentation, ANALOG concluded that "our first impression ... is mixed but mostly optimistic". The magazine warned, however, that because of "Atari's sluggish marketing", unless existing customers persuaded others to buy the XL models, "we'll all end up marching to the beat of a drummer whose initials are IBM'.
Tramiel takeover, declining market
Although Commodore emerged intact from the computer price wars, conflict 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 Tramiel took over, 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 cancelled, often with the new management 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. 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". 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.
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. "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".
Computer Gaming World that month stated "games don't come out for the Atari first anymore". In April the magazine published a survey of ten 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. 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", and in 1987 MicroProse explicitly denied rumors that it would release Gunship for the Atari, stating that the market was too small. Lack of products remained a problem, Antic stating in May 1988 that "the biggest problem facing Atarians today is the difficulty of finding software and other products for our computers. Product unavailability is especially severe for the 8-bit Atari". The magazine urged readers to "SUPPORT Atari software publishers by buying the programs you want—DON'T trade illegal copies with your friends!"
Tramiel era: XE series
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-Compatible Eight Bit). 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.
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.
The XE line suffered from severe reliability issues. The quality of the PCBs was poor, with thin, easily damaged wire traces, and most machines were equipped from the factory with Micron Technologies 64kx1 RAM chips, which had a high failure rate. It was a common practice to install at least one RAM chip from a better-quality brand such as NEC so the computers would pass factory Q/C inspection.
XE Game System
Atari 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.
End of support and legacy
The aging 8-bit line found a market in parts of Europe during the late 1980s and a few current arcade titles such as Gauntlet and Arkanoid were ported for it. Datasoft was one of the last significant North American companies to develop Atari 8-bit software, continuing to put out new games for them until the company closed its doors in 1988.
In 1992, Atari Corp. officially dropped all remaining support for the 8-bit family.
In 2006 Atari consultant and historian Curt Vendel, who designed the Atari Flashback for Atari, Inc. in 2004, claimed that Atari released the 8-bit chipset into the public domain. There is agreement in the community that Atari authorized the distribution of the Atari 800's ROM with the Xformer 2.5 emulator, which makes the ROM legally available today as freeware.
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 the address space that is visible to the 6502. Some of the coprocessors use data stored in RAM, notably ANTIC's display buffer and Display List, 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 a sequence of instructions known as a display list. An instruction adds one row of the specified graphics mode to the display. Each mode varies based on whether it represents text or a bitmap, the resolution and number of colors, and its vertical height in scan lines. An instruction also indicates if it contains an interrupt, if fine scrolling is enabled, and optionally where to fetch the display data from memory.
Since each row can be specified individually, the programmer can create displays containing different text or bitmapped graphics modes on one screen, where the data can be fetched from arbitrary, non-sequential memory addresses.
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 stream then passes to GTIA which applies the playfield colors and incorporates Player/Missile graphics (sprites) for final output to a TV or composite monitor. Once the display list is set-up, the display is generated without any direct CPU intervention.
There are 15 character and bitmap modes. In low-resolution modes, 2 or 4 colors per display line can be set. In high-resolution mode, one color can be set per line, but the luminance values of the foreground and background can be adjusted. High resolution bitmap mode (320x192 graphics) produces NTSC artifacts which are "tinted" depending on the color values; it was normally impossible to get color with this mode on PAL machines.
For text modes, the character set is easily redirected by changing a register, allowing the user to create custom character sets. 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 (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 (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.
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 chroma signals, which are mixed to form an analog 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 chip (Peripheral Interface Adapter, 6520) commands and IRQs, plus controlling the 4 joystick movements on 400/800 and later RAM banks and/or ROM(OS/BASIC/Self-test) enables for XL/XE lines). 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—was used in many Atari coin-op arcade machines of the 1980s, including Centipede and Millipede, Missile Command, Asteroids Deluxe, Major Havoc, and Return of the Jedi.
- 400 and 800 (1979) – original machines in beige cases, 400 has a membrane keyboard, 800 has full-travel keys, two cartridge ports, monitor output. Both machines have expandable memory (up to 48 KB), the slots were easily accessible in the 800. Later PAL versions have the 6502C processor.
- 1200XL (1983) – new aluminum and smoked plastic case, 64 KB of RAM, only two joystick ports. Help key, four function keys. Older software, if it was written improperly, caused compatibility problems with the new OS.
- 600XL and 800XL (1983) – replacements for the 400, 800 and 1200XL sans function keys. 600XL has 16 KB of memory, PAL versions have a monitor port, 800XL has 64 KB and monitor output. Both have built-in BASIC and an expansion port known as the Parallel Bus Interface (PBI). Last produced PAL units were marked "800XLF" on the motherboard and contained the Atari FREDDIE chip and BASIC rev. C.
- 65XE and 130XE (1985) – A repackaged 800XLF with new cases and keyboards. The 130XE has 128 KB of RAM and an Enhanced Cartridge Interface (ECI) instead of a PBI. The first revisions of the 65XE had no ECI or PBI, while the later ones contained the ECI. The 65XE was relabelled as 800XE on some European markets.
- XE Game System (1987) – a game machine in a light beige case, with a detachable full-travel keyboard similar in style and feel to that of the Atari ST.
- 1400XL – Similar to the 1200XL but with a PBI, FREDDIE chip, built-in modem and a Votrax SC-01 speech synthesis chip. Cancelled.
- 1450XLD – a 1400XL with built-in 5¼″ disk drive and expansion bay for a second 5¼″ disk drive. Code named Dynasty. Made it to pre-production, but got abandoned by Tramiel.
- 1600XL – codenamed Shakti, this was dual-processor system with 6502 and 80186 processors and two built-in 5¼″ floppy disk drives.
- 1850XL - codenamed Mickey, this was to use the "Lorraine" (aka "Amiga") custom graphics chips
- 900XLF – redesigned 800XLF. Became the 65XE.
- 65XEM – 65XE with AMY sound synthesis chip. Cancelled.
- 65XEP – "portable" 65XE with 3.5" disk drive, 5" green CRT and battery pack.
During the lifetime of the 8-bit series, Atari released a large number of peripherals including cassette tape drives, 5.25-inch floppy drives, printers, modems, a touch tablet, and an 80-column display module.
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 peripherals made them cost more than the equivalent "dumb" devices used by other systems of the 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. 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, which became the platform's killer app, akin to VisiCalc for the Apple II in its ability to persuade customers to buy the computer.
Chris Crawford and others at Atari published detailed technical information in De Re Atari. In 1982 Atari published both the Atari Home Computer System Hardware Manual and an annotated source listing of the operating system. These resources resulted in many books and articles about programming the computer's custom hardware.
Because of graphics superior to that of the Apple II 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.
The Atari 8-bit computers came with an operating system built into the ROM. The Atari 400/800 had the following:
- OS Rev. A - 10 KB ROM (3 chips) early machines.
- OS Rev. B - 10 KB ROM (3 chips) bug fixes. Most common for 400/800.
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.
- OS Rev. 10 - 16 KB ROM (2 chips) for 1200XL Rev A
- OS Rev. 11 - 16 KB ROM (2 chips) for 1200XL Rev B (bug fixes)
- OS Rev. 1 - 16 KB ROM for 600XL
- OS Rev. 2 - 16 KB ROM for 800XL
- OS Rev. 3 - 16 KB ROM for 800XE/130XE
- OS Rev. 4 - 32 KB ROM (16 KB OS + 8 KB BASIC + 8 KB Missile Command) for XEGS
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
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.
- DOS 1.0 - Initial DOS for Atari.
- DOS 2.0S, 2.0D - Improved over DOS 1.0, became the standard for the 810 disk drive. 2.0D was for the never-released 815 drive.
- DOS 3.0 - Came with 1050 drive. Used a different disk format from previous DOSes, and was incompatible with DOS 2.0, making it very unpopular.
- DOS 2.5 - Replaced DOS 3.0 with later 1050s. Functionally identical to DOS 2.0S, but able to read and write enhanced Density disks.
- DOS 4.0 - Designed for 1450XLD, cancelled, rights given back to the author.
- DOS XE - Designed for the XF551 drive.
Playfield graphics capabilities
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.
|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.|
|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|
|C||14 (XL OS)||128/160/192||1||16/20/24||2||1|
|E||15 (XL OS)||128/160/192||1||32/40/48||4||1|
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.|
- 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
- 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.
- 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.
- There is an "Atari key" between the / and shift, whereas a typical keyboard would extend the shift key into this area.
- A 6502C was simply a version of the 6502 that was able to run at speeds up to 4 MHz. The A models ran at 1, and the B's at 2. The basis for SALLY was a 6502B.
- The +12V was typically used to power RS-232 devices, which now required an external power source.
- No cash was required, instead Warner had the right to purchase $240 million in long-term notes and warrants, and Tramiel had an option to buy up to $100 million in Warner stock.
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