A Quick History...
The Atari 400/800 computers were announced to the world in December 1978 at a time when the computing world was made up of mainframes and mini-computers. Only a few micros had started to appear, such as the TRS-80 and the Commodore PET.
In November 1979 units were ready for shipping and from their first few days of sales, the Atari's were in demand.
The new computers had capabilities that no other manufacturer could match at the time and their new technology trounced the competition.
Beneath the ugly cases was an impressive engine - the MOS Technology 6502C CPU.
The machines also had four-voice sound and a very wide 3.5 octave range.
To really put things into perspective here - the Sinclair ZX81 which launched 2 years later only had two colours (black and white) and no sound capabilities whatsoever...
The Atari 400
The 400 had a membrane keyboard with no moving keys - it wasn't easy to type quickly on, with no key movement, but it could be easily wiped clean after being used by children. Atari used this as a selling point (to hide the fact that it was a cost cutting exercise) in its promotion of the machine as a "family computer".
The big technical advance was the use of the first custom-built "ANTIC" co-processor, which stood for "Alpha-numeric Television Interface Circuit" which was used to control the TV display. It had its own dedicated instruction set which could write data to RAM using Direct Memory Access.
Other key new bespoke chips included the "CTA" (Colour Television Interface Adaptor) which was responsible for colour graphics and collision detection and featured "PMG" (Player/Missile Graphics) technology, opening up endless gaming possibilities.
On the I/O side of things, the joystick ports were intelligent and could send data to to control other devices, such as robotics and phone diallers. There was a cartridge port and connections for cassette use using its own player/recorder.
There was no BASIC in ROM and a cartridge had to be purchased.
Early models (rare and collectable now) had 8K of RAM - the later models had 16K.
The Atari 800
The 800 came with 48K of RAM and a second cartridge port, which got over the limitations of the 400 where you had to choose between using BASIC, using a games cartridge, or plugging in extra memory. There were also user accessible expansion slots for RAM/ROM.
There was a proper typewriter-style switch keyboard and RGB (as well as RF) suggesting that the 800 was aimed more at the business market, leaving the 400 for games.
Atari had the benefit of its massively successful coin-operated video game market as direct copies of the games were sold on cartridges so you had the real thing at home and not a poor clone with other home micros had to put up with.
These machines were expensive though, and if Atari had made these more accessible price wise, it could have cleaned up the entire home computer market.
The XL Series
Atari released the next generation of computers in 1982, and suffered a very shaky start.
The first offering was the 1200XL which was released only on the US market. It had a modified 6502C CPU and other bespoke IC's which meant a new Operating System which couldn't use the massive back catalogues of software.
In effect the machine launched like any other computer brand new to the market with very little software available.
The 1200XL was a flop and production stopped after just 4 months.
The Atari 600XL and 800XL
Learning quickly from the mistakes of the 1200XL, the new machines had very few differences in the extended operating system and were almost fully compatible with the software back catalogue.
They included new 24K ROMS as BASIC was now brought on board. All of the custom chips were retained (and the CTIA was later upgraded) so the machines were technically identical to the earlier models, but the internal layout changes of the new machines meant better looking and cheaper to produce cases could be used.
The only other enhancement was the addition of another Parallel Bus Interface (PBI).
The XE Series
Atari's Consumer Electronics Division and Home Computer Division was sold to Tramiel Technologies Ltd in July 1984 and the holding company was renamed to the Atari Corporation.
The XL series was dropped and in January 1985, the Atari 65XE and 130XE were launched in new attractive cases which would be carried forward into the 16-Bit Atari ST range.
The 65XE was really just a remake of the 800XL without the additional PBI, but the 130XE was the pinnacle of Atari's 8-Bit production.
It has 128K of RAM, a new RAM address multiplexor used for direct RAM access (the "Freddie" chip), and a re-engineered PBI called the "Enhanced Cartridge Interface". It had the best of all the Atari 8-Bit technology.
The XEGS (XE Games System) was the final 8-Bit from Atari - marketed as a console, it was a true 8-Bit computer with 64K of RAM and a detachable keyboard. It still had BASIC in ROM and the "Missile Command" game.
Atari now turned all of its technical attention to the 16-Bit range, although it still continued to manufacture the 8-Bit machines until January 1992 when it finally closed the 8-Bit production lines...