Science Fair Project Encyclopedia
Atari 8-bit family
Atari built a series of 8-bit home computers based on the MOS Technology 6502 CPU, starting in 1979. Over the next decade several versions of the same basic design would be released, but the models remained largely identical internally.
As soon as the Atari 2600 was released the engineering team went back to design its eventual replacement. The newer design would be faster, have better graphics, and include much better sound hardware. Work continued throughout 1978, primarily working on the much-improved video hardware known as the CTIA (the 2600 used a chip known as the TIA).
However, at this point, the home computer revolution took off in the form of the Apple II family, Commodore PET and TRS-80. Atari management saw this as a golden opportunity to re-purpose the machines, and started research on what would be needed to produce a workable home computer of their own. This included support for character graphics (something the 2600 didn't support), some form of expansion for peripherals, the BASIC programming language, and a keyboard.
All aspects of the machine were considered open to new solutions, and the machine ended up with its own BASIC, a wonderfully simple peripheral system known as SIO (Serial I/O), and a very powerful character/display driver known as ANTIC. Unlike the 2600 where the video was controlled solely by the TIA moving sprites (known as player/missile graphics in Atari lingo) around a colored background, in the new machines the ANTIC did most of the work drawing the screen (including the ATASCII characters), which the GTIA then colored and added the sprites. This separation of duties allowed both chips to be as powerful as possible, and the machine's graphics were the best on the market until the release of the Commodore 64 in 1982.
The ANTIC was one of the first graphical Co-processors ever, with its own machine language and memory access, which was made possible by using a non-standard 6502 chip, nicknamed SALLY, that could be halted when the ANTIC needed memory access. (This processor was later identified as 6502c.)
Another custom support chip, named POKEY, was responsible for reading the keyboard, generating sound and serial communication (The latter in conjunction with the PIA). The same POKEY chip was also a very common solution for sound effects and music in arcade games in the 1980s, producing a distinctive square wave flavor that is popular among chip tune aficionados.
Eventually they identified two "sweet spots" for such machines, the low-end Candy and high-end Colleen. Both ran at 1.79 MHz (PAL version, European) or 1.77 MHz (NTSC version, US), which made them almost twice as fast as most machines of the era; the Apple II and Commodore PET ran at 1 MHz, the TRS-80 was at 2.03 MHz but was actually about 1/2 of the speed due to its processor, the Zilog Z80's, design. The primary difference between the two was expandability, Colleen would include a number of memory slots, monitor output and a full keyboard, while Candy used a plastic "membrane keyboard" and didn't include any memory slots. Both machines were built like tanks with huge internal aluminum shields, a side effect of meeting a FCC specification that was soon to be removed anyway (the first model of the TRS-80 actually never met that FCC spec).
The machines were brought to market in February 1979 as the 400 and 800, although they weren't widely available until late 1979. The names originally referred to the amount of memory, 4KB RAM in the 400 and 8KB in the 800. However by the time they were released the prices on RAM had started to fall, so the machines were instead released with 8KB and 16KB respectively, making the naming somewhat superfluous. The 800's expansion system allowed it to be fitted with up to 48KB RAM. The ATARI BASIC interpreter came as a ROM cartridge (later, a more advanced Microsoft BASIC would also become available).
The 800 was rather complex and expensive to build and the 400 didn't compete technically with some of the newer machines appearing in the early 1980s, so in 1982 Atari started the Sweet 16 project to address these issues. The result was an upgraded set of machines otherwise similar to the 400 and 800, but much cheaper to produce. Newer fabs allowed a number of chips in the original systems to be condensed into one. For comparison the original 800 used seven separate circuit boards (many of them small), while the new machines used only one. Sweet 16 also addressed problems with the 800 by adding a new expansion chassis as well. Like the earlier machines, the Sweet 16 was intended to be released as the 1000 with 16KB and the 1000XL with 64KB.
But when the machines were actually released there was only one version, the 1200XL. A number of problems in this machine, including a change in its operating system which made many programs written for the 400/800 computers incompatible, made the machine a flop. This was quickly addressed in the hastily-completed 600XL and 800XL, which were largely identical to the original Sweet 16 specifications. However the 1200XL was released at potentially the exact wrong time. By the time the new machines replaced it the Commodore 64 had already become the market leader, and Atari was unable to address this. This also triggered the demise of the 1450XLD, which boasted a built-in 3½" diskdrive but was never released.
The final machines in the series were there 130XE and 65XE. These were really cut-down versions of the 600XL and 800XL in much cheaper cases, a result of Jack Tramiel's efforts to wring every dollar out of the platform before finally killing it. The X in XE stood for XL-Compatible.
A theory for why the number 65 was used for the first machine in the XE series is because Atari wanted their machine-numbers to correspond with the amount of RAM they came with, but as Commodore already used the numbers 64 and 128, Atari decided to add one to 64 and chose 65. All subsequent model-numbers were multiples of 65 instead of 64. This numbering-scheme was also used in the Atari ST line of computers as well.
An additional 800XE was available in Europe (mostly Eastern Europe), it was basically a 130XE with half the memory. Almost as an afterthought, there was also the XE Game System (XEGS), released in 1987. Launched at the very end of the family's market life, the XEGS was sold bundled with its detachable keyboard, a joystick and a lightgun, and a couple of game cartridges.
- 400 and 800 (1979) – original machines in beige cases, 400 had membrane keyboard, 800 had full-travel keys
- 1200XL (1982) – new aluminum and smoked plastic cases, 64KB of RAM, new but buggy OS and BASIC, which made it a market flop
- 1450XLD – basically a 1200XL with built in 3½" diskdrive (never released, small numbers (5) leaked out)
- 800XL and 600XL (1982) – replacements for the failed 1200XL, basically fixed the OS and BASIC bugs and added an expansion port; the 16KB 600XL was later dropped
- 130XE and 65XE (1985) – 800XLs repackaged with highly inexpensive cases and keyboards with 128KB of RAM in the 130
- XEGS (1987) – a game machine in a light beige case, with a detachable full-travel but slightly "mushy" keyboard (Atari ST'ish)
Atari's peripherals were named after the machines they were intended to be used with, so in general they have names like "410" and "1050". All of them used the proprietary SIO port, which allowed them to be daisy chained together into a single string; a method also used in Commodore's home computers from the VIC-20 onwards. This resulted in far less "cable spaghetti" on the desk, but it also meant plugging in "standard" components like printers and modems was practically impossible without the purchase of separate conversion units (in Atari's case, the 850 interface expansion system).
- 410 tape drive, 600 bit/s on cassettes
- 810 5¼" floppy disk, single-density single-sided, 90KB
- 815 dual 5¼" floppy disks, double-density single-sided, 180KB (only small numbers produced)
- 820 printer, 40-column dot matrix on adding machine paper
- 822 printer, 40-column thermal on slightly wider paper
- 825 printer, 80-column dot matrix (Centronics 737)
- 830 300-baud modem, using an acoustic coupler, used RS-232 so required an 850 (Novation CAT)
- 835 300-baud modem, direct connect, basic Hayes compatible with SIO interface
- 850 expansion system, included four RS-232 ports and one Centronics parallel port
- 1010 tape drive, a smaller replacement for the 410
- 1020 plotter, 20, 40 or 80-column with 4-colors on paper similar to the 822
- 1025 printer, 80-column dot matrix (Okidata ML-80)
- 1027 printer, 80-column letter quality daisy wheel (Mannesmann Tally Riteman LQ)
- 1029 printer, 80-column lower-quality 7-pin dot matrix sold in Europe (Seikosha mechanism)
- 1030 300 baud modem, direct connect
- 1050 5¼" floppy disk, "enhanced density" format single-sided, 130KB
- 1090 expansion system, 5 slots in a large case (never released, small numbers leaked out)
- XEP80 80-column display module, parallel port
- XC11 tape drive
- XC12 tape drive (small model like the 1010, sold worldwide)
- XF551 5¼" floppy disk, double-density double-sided, 360KB
- XMM801 printer, 80-column dot matrix
- XDM121 printer, 80-column letter quality daisy wheel
- XM301 300 baud modem
- SX212 1200 baud modem (also included RS-232 for use on Atari ST computers)
Atari also produced a number of other tape drives for use in eastern Europe where they continued to sell into the late 1980s due to their low cost. Some of these included various "high-speed" modes which made them almost as fast as early disk drives.
In addition to the list above, Atari failed to release a huge selection of machines and peripherals that were otherwise completed. See the externally linked FAQ below for details.
The Atari 8-bit computers came with an operating system built into the ROM. The first Atari 400/800s had the Rev. A OS, and later 400/800s had it upgraded to Rev. B. The later Atari 8-bit models all had an aditional OS revision.
The standard Atari OS only contained very low-level routines for accessing disk drives. An extra layer (a Disk Operating System) was added to assist in organising higher-level disk access (such as file systems). This was called (Atari) DOS. As DOS was not part of the ROM, it was booted from a floppy disk (a method similar to most home computers of the era, but contrary to the British BBC Micro, whose optional Disk File System, DFS, did come on ROM chips to be installed in the computer; and Commodore's machines, which had their DOS (Commodore DOS) located in the disk drives' ROMs — see e.g. the CBM 1541).
Several third-party replacement OSes were also available. The most used is Q-MEG .
Available programming languages
- Atari BASIC – This was the original BASIC for the Atari 8-bit family. Came as a ROM cartridge with the Atari 400/800 models, but was built into the computer's ROM in later models.
- Atari Microsoft BASIC – A version of BASIC for the Atari 8-bit family released by Atari that was more like the industry standard Microsoft BASIC. This did not catch on.
- Turbo Basic XL – An improved version of Atari BASIC released by a third party that is not only faster, but offers many more commands. There is also a compiler that makes Turbo-BASIC XL programs even faster by compiling them int machine-language binaries.
- 6502-Assembler – A 6502 assembler editor and compiler was released by Atari in cartridge form. Several 3rd-parties made improved 6502 assemblers.
- Deep Blue C – A C compiler.
After Atari's 8-bit machines entered the realm of retrocomputing in the late 1990s, cross platform development tools such as XASM, TASM, and cc65, most commonly run on PCs, have been much used by enthusiasts to do programming intended for the machines.
- Atari 8-Bit Computers: Frequently Asked Questions
- Atari Historical Society
- The Atari 8-bit Computer WebRing
- Atari 8-bit Resort
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