Atari 400

Atari 400
	Atari 400 home computer (1979)
Specifications
Manufacturer	Atari, Inc.
Type	Home computer
Released	November 1979
Discontinued	1983
Intro price	US$550 (1979)
CPU	MOS Technology 6502 @ 1.79 MHz (NTSC) / 1.77 MHz (PAL)
Memory	8 KB RAM (original), later models 16 KB or 48 KB RAM
Storage	External cassette tape (410 Program Recorder), optional 810 5.25" floppy disk drive
Display	40×24 text, 320×192 pixels (max), 128 colours (NTSC: 256 hues x 128 luminances)
Sound	POKEY: 4 channels, 8-bit, noise, random, keyboard scan
Dimensions	41 cm × 24 cm × 9 cm
Weight	3.2 kg
OS / Firmware	Atari BASIC (cartridge), Atari OS in ROM
Successor	Atari 800
Codename	Candy
Model no.	CX2624

The Atari 400 is an 8-bit home computer introduced by Atari, Inc. in November 1979. Designed as a more affordable and child-friendly sibling to the Atari 800, the 400 featured a membrane keyboard and robust plastic case, targeting the home computing and educational markets.

Architecture and Processor

At the heart of the Atari 400 is the MOS Technology 6502 microprocessor, running at:

1.79 MHz (NTSC systems)
1.77 MHz (PAL systems)

The system architecture is built around custom Atari co-processors:

ANTIC – programmable video interface controller, responsible for display list processing and graphics generation.
CTIA/GTIA – handles colour, player/missile graphics (sprites), and video output.
POKEY – manages sound generation, keyboard scanning, serial I/O, and random number generation.

This multi-chip design allowed the Atari 400 to deliver advanced graphics and sound capabilities for its time.

Memory and Storage

The Atari 400 was originally shipped with 8 KB RAM (expandable to 16 KB and later 48 KB via third-party upgrades). ROM contained the system OS and I/O routines. Application software and the Atari BASIC interpreter were supplied on plug-in cartridges.

Storage options included:

410 Program Recorder – external cassette tape drive for program and data storage.
810 floppy disk drive – optional 5.25" single-sided, single-density drive (via SIO port).

Display and Graphics

Graphics capabilities were a major strength of the Atari 400, provided by the ANTIC and CTIA/GTIA chips:

Text modes: 40×24 and 20×24 characters
Graphics modes: up to 320×192 pixels (bitmap), with multiple colour and resolution options
Colours: Up to 128 (NTSC) or 104 (PAL) simultaneous colours via palette and luminance controls
Sprites: 4 player and 4 missile hardware sprites ("player/missile graphics")
Smooth scrolling and fine control over display via programmable display lists

The system could output video via RF modulator (for TVs) or composite video (with modification).

Sound Capabilities

Sound was generated by the POKEY chip, offering:

4 independent audio channels
8-bit resolution, with selectable frequencies and noise generation
Programmable audio control for effects and music
Integrated keyboard scanning and random number generator

The POKEY chip enabled complex sound effects and music, making the Atari 400 popular for gaming.

Input/Output and Expansion

The Atari 400 included the following I/O and expansion features:

Cartridge slot – for games and software (Atari BASIC, educational titles, etc.)
4 joystick ports – supporting Atari-compatible digital controllers
SIO (Serial Input/Output) port – daisy-chainable connection for cassette, disk drives, printers, modems, and other peripherals
RF output – for connection to standard television sets

Unlike the Atari 800, the 400 did not include user-accessible internal expansion slots and was limited to its factory RAM configuration (though third-party upgrades became available).

PCB Schematics & Service Manual

**Atari 400 Main Boards**
Logic Board	Logic Board Schematic
Atari 400 Logic Board	File:Atari 400 800 Home Computer Schematics.pdf

Official service manuals and schematics are available via the Atari 400 / 800 Field Service Manual

Gallery

Atari 400 front view
Atari 400 Interfaces
Atari 400 logic board (main PCB)
Cartridge slot open