Atari 8-bit computer peripherals
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.
List of peripherals
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.)
400/800 era (1979-1982) 
- 410 tape drive, 600 bit/s on cassettes
- There exist several variants of the 410; in particular, later models sold under the "410" name were both internally and externally noticeably different in appearance from the early ones.
- The 410 used stereo with the data recorded on one track and the other track holding audio that could be fed through the 400 or 800's sound output (as demonstrated by the language courses). The tape could also be programmatically stopped and started, provided the 'Play' button was engaged.
- 810 5¼" floppy disk, single-density single-sided, 90 KB
- 815 dual 5¼" floppy disks, double-density single-sided, 180 KB (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 (relabelled 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
- CX-85 Numerical Keypad, external keypad that plugs into the joystick ports.
XL era (1982-1984)
- 1010 tape drive, a smaller replacement for the 410
- 1020 color printer, 40-column plotter with 4 pens
- 1025 printer, 80-column dot matrix (Okidata ML-80)
- 1027 printer, 80-column letter quality that printed with a 5-wheels-on-a-drum system kept inked by a top-mounted roller (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, 130 KB
- 1055 3½" floppy drive (never released)
- 1064 memory module, 64 KB memory expansion for 600XL
- CX77 touch tablet
XE era (1985 onwards)
- XEP80 interface module for 80-column and parallel printer, based on NS405, an 8048 based chip. Attached via a joystick port controlled at 15625 baud horizontal video timing.
- XC11 tape drive
- XC12 tape drive (small model like the 1010, sold worldwide). Similar models were released, mainly in Eastern Europe. These included:-
- XCA12 (same case as XC12)
- CA12 (same case as XC12)
- XL12 tape drive (an XC12 with minor changes)
- XC13 - "T2000 ready" version of XC12
- XF351 3½" floppy drive (never released)
- XF551 5¼" floppy disk, double-density double-sided, 360 KB
- 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)
References and notes
- The Atari Sweet-16 Project, landley.net. Article retrieved 2007-03-18.
- NS405: the heart of the XEP80
- "What other cassette recorders can I use with my Atari?", Atari 8-bit computers FAQ. Version used last updated 2006-11-07, accessed 2006-11-08.
- Atari 8-Bit Computers: Frequently Asked Questions- includes information on unreleased peripherals.