Atari 800

Atari 800
	Atari 800 Home Computer (1979)
Specifications
Manufacturer	Atari, Inc.
Type	Home Computer
Released	November 1979
Discontinued	1983
Intro price	US$995 (1979)
CPU	MOS Technology 6502 @ 1.79 MHz (NTSC) / 1.77 MHz (PAL)
Memory	8 KB – 48 KB RAM (user expandable), 10 KB ROM
Storage	External cassette tape (410/1010), optional 5.25" floppy disk drive (810/1050)
Display	40×24 text, up to 320×192 pixels, 128 colours (NTSC: 16 hues × 8 luminance)
Sound	4 voices, 3.5 octaves (POKEY chip)
Dimensions	48.3 cm × 34.3 cm × 10.2 cm
Weight	5.4 kg
OS / Firmware	Atari OS (in ROM), Atari BASIC (cartridge)
Successor	Atari 800XL
Codename	Colleen
Model no.	800

The Atari 800 is an 8-bit home computer introduced by Atari, Inc. in late 1979, designed as a robust, expandable system for the home and education markets. It was part of the original Atari 8-bit family, featuring advanced graphics and sound capabilities for its era.

Architecture and Processor

The Atari 800 is built around the MOS Technology 6502 microprocessor, running at:

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

The system architecture is highly modular, utilising custom coprocessors:

ANTIC (Alphanumeric Television Interface Controller) – handles display list processing and graphics DMA.
CTIA/GTIA (Color Television Interface Adapter / Graphic Television Interface Adapter) – manages colour, sprites (player/missile graphics), and collision detection.
POKEY (Potentiometer and Keyboard Integrated Circuit) – responsible for sound, keyboard scanning, and serial I/O.

This coprocessor-based design enabled the Atari 800 to deliver advanced multimedia features and flexible video modes.

Memory and Storage

The Atari 800 shipped with:

8 KB RAM standard (early units), expandable to 48 KB RAM via plug-in memory cards.
10 KB ROM, containing the operating system and built-in diagnostics.

Storage options included:

Atari 410/1010 Program Recorder – external cassette tape drive for data and program storage.
Atari 810/1050 Disk Drive – optional 5.25" floppy disk drive for faster, more reliable storage.
Cartridge slot – for instant-load software and BASIC interpreter.

Display and Graphics

Graphics capabilities were a major strength of the Atari 800, driven by the ANTIC and CTIA/GTIA chips:

Text modes: up to 40 columns × 24 rows.
Graphics modes: resolutions from 40×24 up to 320×192 pixels.
Colour: up to 128 colours (NTSC: 16 hues × 8 luminance levels).
Sprites: 4 "player" and 4 "missile" hardware sprites (player/missile graphics) with collision detection.
Smooth scrolling, programmable display lists, and fine control over video memory.

These features allowed for arcade-quality visuals and animation, setting the Atari 800 apart from most contemporaries.

Sound Capabilities

Audio is provided by the POKEY chip, offering:

4 independent audio channels (voices).
Each channel covers 3.5 octaves.
Programmable frequency, volume, and distortion settings.
Additional features: random number generation and keyboard scanning.

The POKEY's flexibility enabled a wide range of sound effects and music, making the Atari 800 popular among game developers.

Input/Output and Expansion

The Atari 800 was designed for expandability and robust I/O:

Two cartridge slots (one primary, one auxiliary) for software and hardware expansion.
Four joystick ports – compatible with Atari-style controllers.
Peripheral Interface Bus (SIO) – daisy-chain connection for disk drives, printers, modems, and cassette recorders.
Composite and RF video outputs – for connection to TVs and monitors.
Parallel bus expansion slot (underneath) for memory and future upgrades.
Full-travel keyboard – 57 keys, including function keys and a HELP key.

The system's modular design and shielded, rugged case made it suitable for both home and educational use.

PCB Schematics & Service Manual

The Atari 800 consists of a main logic board and plug-in memory cards. Its robust, shielded construction was intended to meet stringent FCC requirements for home electronics.