This article covers the range of peripherals available for Atari's 8-bit home computer range (including the 400/800, XL and XE series machines).
Because the Atari 400/800 8-bit computers included an RF modulator, stringent FCC regulations limiting radio emissions applied to the Ataris. Consequently, the Atari 400/800 systems internal construction used large metal frames as Faraday cages to prevent emissions. At this time most other computers used plug-in internal cards to add connections for peripherals. The Atari computers' internal structure made this impractical.
To permit easy expansion Atari developed the SIO (Serial Input/Output) bus. This bus daisy chains together all Atari peripherals into a single string—disk drives, printers, modems, RS-232 interfaces. 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.
Both the names and styling of Atari's 8-bit peripherals generally matched the current computer range at the time they were released. Thus, they can be divided into one of three groups- those corresponding to the 400/800 era (4xx/8xx), the XL era (10xx) and the XE era (beginning with 'X') respectively. (The XL-era naming reflected Atari's original intention to launch an "Atari 1000" line.) Nevertheless, it should be emphasised that these are superficial issues; the majority of peripherals listed here will work with any 8-bit Atari computer.
In addition to those listed below, Atari failed to release a huge selection of machines and peripherals that were otherwise completed. (See the externally linked FAQ below for details.)