The Atari 400 and 800 were the first home computers to use custom coprocessors and the first to use "sprites" and special video interruptions like display lists, features that will be implemented later on the Commodore 64 and Amiga (Atari 400/800 and Amiga were designed by Jay Miner).
It offered high graphic resolution, lots of colors and great sound capabilities, more than other computers could do then ! The two models had same characteristics, the 400 is the low-cost version, it has only 16 KB (instead of 48 KB), one cartridge port (two for the 800) and a membrane keyboard (a typewriter style keyboard one for the 800).
Originally, the 400 was sold with 8 KB RAM, but later most 400s were shipped with 16 KB. The 800 was expandable to 48 KB by adding cartridges, as the case opened upwards to reveal 3 slots behind the program cartridge slots. The expansion in the 400 (which had an identical motherboard) was only available by removal of the top half of the case, as it did not open past the (single) program cartridge slot, and was only possible through a registered Atari dealer.
The Atari 400 was known inside Atari as code name "Candy".
Tristan Smith adds:
The keyboard was very much disliked on this thing. There were several replacement keyboards on the market. Some connected via cable to one of the ports (and required a TSR program be loaded). Others required you open the system up and replace the actual keyboard. One that I remember was adhesive! It had all the keys on it with "eraser" type rubber things on the underside. You peeled off the backing and attached it over the membrane keyboard. When you pressed a key, the eraser would press the membrane key. As unresponsive as that was, it was still better than the original.
Not too many people realized that the Joystick ports were true I/O and could be used to control devices. There were a bunch of items that used the joystick ports. I remember building a phone dialer with them....
Adin Seskin reports:
The sound on these computers was particularly impressive. Apart from 4 square-wave generators, you could covert them to 2 voices with a far greater frequency range, and the voice generator could also produce general video-game noises very easily - explosions, machine noises etc.
At one point a surprisingly good software-based speech synthesizer was developed, to exploit the sound chip. It had to disable all interrupts, especially video DMA, in order to generate the sounds, which rather limited its use.
Not many people know that the same sound generator was also used for data encoding when saving programs or data to the cassette or disk systems.
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I have a 400. I made a keyboard for it as per the article in December 1982 Creative Computing (https://archive.org/details/creativecomputing-1982-12). I bought a kit from some company I cannot remember that upgraded it to 64K (cutting traces and soldering some wires was involved) and installed it. I also bought the Assembler cartridge for it and took a course in how to program it. I had a lot of fun with that machine. It''s in a box in the garage, I should get it out and see if it still works.
Tuesday 1st September 2020
RonF (Illinois, USA)
I had an Atari 400 when I was about 13. Me and my older brother used to love writing games for it and using it to switch on light bulbs etc. via relays. The joystick ports were ideal for this!
When we started working for an electronics firm, we actually used a 400 to control and test digital PABX telephone exchanges and later design 6502-based, fully automated test rigs for the firm.
Recently, my mother was clearing out her attic and asked me if ''this'' was any use? It was my old Atari 400! I thought it was long-gone!
This year I opened it up, repaired it and finally upgraded it to 48K!
Friday 5th October 2018
David Mc (UK)
Atari 400 is the best home computer for videogame until Commodore 64. I love its vintage look membrane keyboard!
ANTIC (Scrolling, Sprites, Video), CTIA / GTIA (Color, Sprites, Collisions), POKEY (timers, sound, keyboard, serial I/O), PIA 6810 (I/O, including the 4 joystick ports)
8 KB or 16 KB (newer models)
40 x 25
several graphic modes, maximum : 320 x 192
16 (each color can have 8 luminances) = 128 colors maximum in the lowest graphic mode (requiring display list interruption to have them simultaneously) and up to 256 colors in some specific modes for machines having the GTIA chip instead of the CTIA
4 voices, 3.5 octaves
SIZE / WEIGHT
Monitor RGB output, RF TV video output, 1 cartridge slot, Atari Serial Input/Ouput (SIO) port, 4 controller jacks