Atari 8-bit family

Atari 8-bit family

The Atari 800, featuring a full keyboard and dual-width cartridge slot cover.
Type	Home computer
Release date	November 1979
Discontinued	January 1992
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	4× 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

The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips. Over the following decade several versions of the same basic design were released, including the original Atari 400 and 800 and their successors, the XL and XE series of computers. Overall, the Atari 8-bit computer line was a commercial success, selling two million units through its major production run between late 1979 and mid-1985,^[1] a total of around 4 million units.^{[citation needed]}

History

Origins

Design of the 8-bit series of machines started at Atari Inc. as soon as the Atari 2600 games console was released in late 1977. The engineering team from Atari Grass Valley Research Center (originally "Cyan Engineering")^[2] 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 1980, three years after the 2600's introduction. What they ended up with was essentially a "corrected" version of the 2600, fixing its more obvious limitations.^[3] 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.

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".^[4] Ray Kassar, the then-new CEO of Atari from Warner Communications, wanted the new chips to be used in a home computer to challenge Apple. 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.

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.

The early machines: 400 and 800

Atari 400 (1979). Featuring a membrane keyboard and single-width cartridge slot cover.

Internal components of the Atari 800 without the heavy aluminum RF shielding. Although the main board has a card edge connector on the rear, it was inside the aluminum shield and unavailable for use.

Atari 800, internal components: * Plastic guide for installing cards/cartridges * Processor board (was hidden inside the aluminum shield) * OS ROM board * Interior of ROM cartridge * 16 kilobyte memory board * 16 kilobyte memory board * 16 kilobyte memory board * Main system board * External I/O and power supply board

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).^[5] 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 would include 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, while Candy used a plastic "membrane keyboard", non-accessible internal slots for memory, and only RF output for video.

At the time, the Federal Communications Commission (FCC) mandated that signal leakage protection in the television frequency range had to be extremely high. As the Atari machines had TV circuitry inside them, they were subject to this rule and 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 devices to connect to the computer through a single shielded connector. What internal slots existed were reserved for ROM and RAM modules.

An overarching goal for the new computer systems was user-friendliness. The Atari computers were designed to minimize handling of bare circuit boards or chips 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 did not require the user enter commands to boot the system. The OS, large and comprehensive for its time, would boot 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 would go to the "Memo Pad" mode allowing the user to type using the built-in full screen editor.

Atari had 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 all of Atari's attempts to pare it down to 8 KB failed. Eventually they farmed out the work to a local consulting firm, Shepardson Microsystems, who recommended writing their own version from scratch, which was eventually delivered (on external cartridge) as Atari BASIC.

The machines were announced in late 1979^[5] as the 400 and 800, although they were not widely available until 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.

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.^[1] Because of this, developers were generally unwilling to use the 800-only right cartridge slot.

Liz

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 tended to ship with much more RAM and an upgraded keyboard.

Another major change was the introduction of the FCC ratings specifically for digital devices in homes and offices. One of the ratings, known as Class B, mandated that the device's RF emissions were to be low enough not to interfere with other devices, such as radios and TVs. Now computers needed just enough shielding to prevent interference (both ways), not prevent any emissions from leaking out. This requirement enabled lighter, less expensive shielding than the previous 400 and 800 computers.

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 Atari 5200/7800 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

1200XL

Atari 1200XL

Released in late 1982, the 1200XL was an odd hybrid of features from the Sweet 8/16 projects. 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. In general terms the 1200XL most closely matched the "high end" Sweet 16 concept.

However the 1200XL also 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 SIO again. Frustrating this was the fact that the +12V pin in the SIO port was left unconnected; only +5V power was available although some devices made use of the +12V line. 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.

The 1200XL ended up with functionality similar to the existing 800, but at a hefty price point. For all of these reasons the 1200XL sold poorly. There is an often-repeated story, perhaps apocryphal, that 800 sales shot up after the release of the 1200XL, as existing owners tried to snap them up before they disappeared.^[6] The machine was discontinued in 1983. There was no PAL version of the 1200XL.

Newer XL machines

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

An Atari 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, but this time Tramiel's supply was stronger than TI's, and he could turn the tables.

Although Atari had never been a deliberate target of Tramiel's wrath, they, along with the rest of the market, were dragged into "his" 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.

Starting with the 1200XL design as the basis for a new line, 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. While the 1200XL fit onto a single board, the new designs were even smaller, simpler, and as a result much less expensive. But 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.

Several versions of the new design, the 600XL, 800XL, 1400XL and 1450XLD were announced at the 1983 Summer CES. The machines had Atari BASIC built into the ROM of the computer and the PBI at the back that allowed external expansion. The machines looked similar to the 1200XL, but were smaller back to front, the 600 being somewhat smaller than the 800 front-to-back (similar to the original Sweet 8 project). The 1400 and 1450 both 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.

The main circuit board of an Atari 800XL

However, the production move ran into unexpected delays. Originally intended to replace the 1200XL in mid-83, the machines did not arrive until late in 1983. 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 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.^[7] 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 eventually 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.^[8] The 1850XLD was to have been based on the custom chipset in the Amiga Lorraine^[9] (later to become the Commodore Amiga).

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 soon 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 protoype 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 Jack Tramiel was primarily focused on developing the 68000-based Atari ST system and bringing in ex-Commodore engineers to work on the ST line.

Tramiel era: XE series and XE Game System

Atari 130XE

Atari XE Game System

Jack Tramiel's Atari Corporation produced the final machines in the 8-bit series, which 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 was functionally equivalent to the 800XL minus the PBI connection. The 65XE (European version) and the 130XE had 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. The 130XE shipped with 128 KB of memory, accessible through bank-selection, and was aimed to appeal at the mass market.^[10]

An additional 800XE was available in Europe (mostly Eastern Europe), which was essentially a 65XE repackaged in order to ride on the popularity of the original 800XL in Europe.^{[citation needed]} Unfortunately, the 65XE and 800XE machines sold in Eastern Europe had a buggy GTIA chip, specifically those machines made in China in 1991.

Finally, with the resurgence of the gaming industry brought on by Nintendo, Atari Corp. brought out the XE Game System (XEGS), released in 1987. The XE Game System was sold bundled with a detachable keyboard, a joystick and a light gun (XG-1), and a couple of game cartridges (Bug Hunt and Flight Simulator II). The XE Game System was essentially a repackaged 65XE, and was compatible with almost all Atari 8-bit software and hardware as a result. Bad marketing and a lack of newer releases hampered sales.

On January 1, 1992, Atari corp. officially dropped all remaining support of the 8-bit line.^[11]

Design

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 set/get 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

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.

CTIA/GTIA

The Color Television Interface Adaptor^[12] (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^[12] (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.^[13]

The CTIA/GTIA receives Playfield graphics information from ANTIC and also controls Player/Missile Graphics (aka sprites). The functionality includes 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.

POKEY

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 and dual-core and quad-core versions of the chip are used in several Atari coin-op arcade machines of the 80s, including Missile Command and Asteroids Deluxe, among others.^[14]

Computer models

• 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 slots (up to 48 KB). Later PAL versions have the 6502C processor.
• 1200XL (1982) – new aluminum and smoked plastic cases, 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 had a monitor port, 800XL have 64 KB and monitor output. Both have built-in BASIC and an expansion port known as the Parallel Bus Interface (PBI).
• 800XLF – 800XL with Atari FREDDIE chip and BASIC rev. C. Released in Europe only.
• 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 U.S./Canadian version of the 65XE has no ECI or PBI.
• XE Game System (1987) – a game machine in a light beige case, with a detachable full-travel but slightly "mushy" keyboard (similar in style and feel to that of the Atari ST).
• 800XE – the final machine in the series. Styling the same as 65XE and 130XE. A 130XE with 128 KB RAM. Mainly seen in Eastern Europe.

• Prototypes/Vaporware (Never Officially Released)
  • 1400XL – Similar to the 1200XL but with a PBI, FREDDIE chip, built-in modem and speech synthesis chip. Cancelled by Atari.
  • 1450XLD – basically 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.[1]
  • 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. Never released
  • 1090XL expansion system, 5 slots in a large case (never released, small numbers leaked out)
  • 1055 3½" floppy drive [2]
  • XF351 3½" floppy drive [3]
  • XF354 3½" floppy drive

Peripherals

Atari 1020 4-color Plotter

During the lifetime of their 8-bit series, Atari released a large number of peripherals. These included:

• Several dedicated cassette tape drives. All were similar, and capable of recording at 600 bit/s on a standard audio cassette. (Unlike some computer systems, it was not possible to use a standard cassette deck with the Atari for this purpose.)
• Various 5.25-inch floppy disk drives, including single, enhanced and true double-density models.
• Several printers of various types; dot matrix, thermal, 4-color plotter and letter-quality daisy wheel.
• Modems, including one model with an acoustic coupler and other direct-connect models.
• Other peripherals, including a Centronics/RS-232 expansion system, numeric keypad, memory module, 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. Devices on the bus have their own IDs and peripherals 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.

Software

Operating system

Built-in

The startup screen of early Atari 8-bit models when no program is loaded. The Memo Pad allows the user to type onscreen using the built-in full screen editor.

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 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. Early models 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.

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

Other software

Amongst the many pieces of software released for the 8-bit Atari computers, a large number of programming languages were implemented, including:-

• Assemblers, via the Atari Assembler Editor, Atari Macro Assembler, MAC/65, and several others.
• BASIC; Atari BASIC was the "standard" BASIC implementation for the 8-bit family, originally a ROM cartridge, and built-in from the 600XL/800XL onwards. Other BASICs included Atari Microsoft BASIC, BASIC A+, BASIC XL, Turbo Basic XL, and Advan BASIC.
• C (Programming Language), via the Deep Blue C, Lightspeed C and cc65 compiler.
• Other languages including LOGO (Atari LOGO), LISP (INTER-LISP/65), PILOT (Atari PILOT), several versions each of Forth and Pascal, Action! (a high performance Atari-specific language from OSS), and WSFN (which stands for nothing).

More recently, cross platform development tools (most commonly run on PCs), have become popular for retrocomputing software development.

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 capabilites 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

Map Modes

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.

Software-driven modes

Due to the 8-bit Ataris' flexibility, it was possible (with clever programming) to create a number of software-driven pseudo-"modes" beyond those directly supported in hardware. These included pseudo-256-color 80 pixel × 1 TV line tall modes and 80 character × 24 text lines displays. One difficulty with these modes was that the grating on PAL and NTSC televisions is very different, as is the update speed and resolution, and so often they would display well on European systems and awfully on US ones, or vice versa. For the same reason they may not display well – or display rather too well – on emulators.

It was also possible by using the Display List Interrupt facility to display far more than the usual number of sprites on the screen, with more colours than available. This is done by writing machine language routines to change the values of hardware registers at different vertical positions on the screen. The machine language routines modifying hardware registers allowed the programmer to move the sprites around and change their colours 'on the fly'. The same technique could be employed to display far more colours than seemingly allowed in any particular graphics mode, which could be mixed and altered at will.

Because the screen memory could be accessed by two pointers and relocated anywhere in available memory, it was also extremely easy to implement hardware scrolling and page flipping to enable easy game design and programming.

There are many examples of demo programs available on the internet, displaying these and other features.

See also

• History of Atari
• A.N.A.L.O.G. magazine
• Antic magazine
• Atari User magazine
• Page 6 magazine
• De Re Atari published by the Atari Program Exchange
• ANTIC
• CTIA and GTIA
• POKEY
• List of Atari 8-bit family emulators

Footnotes

References

External links

General

• The Atari History Museum
• Atari 8-Bit Computers: Frequently Asked Questions
• The Atari 8-bit Computer WebRing
• Stan Veit's Atari 800 History
• ATARI 65 XE with arabic keyboard
• Gamasutra's "A History of Gaming Platforms: Atari 8-bit Computers" by Bill Loguidice and Matt Barton
• Gamasutra's "The History of Atari" Part 1:1971-77 | Part 2:1978-81, by Steve Fulton

Technical information

• Another source of chipset information
• De Re Atari published by the Atari Program Exchange

Software, games, music, demos

• Atari SAP Music Archive
• Atari Archives
• XL Search – A searchable index of files from numerous Atari FTP archives and websites
• Reminiscing: 8-Bit Atari Games
• Database of Atari games, demos and software