Atari 600XL

Atari 600XL
	Atari 600XL home computer
Specifications
Manufacturer	Atari, Inc.
Type	Home Computer
Released	1983
Discontinued	1984
Intro price	US$199 (1983)
CPU	MOS Technology 6502C (SALLY) @ 1.79 MHz (NTSC) / 1.77 MHz (PAL)
Memory	16 KB RAM (expandable to 64 KB), 24 KB ROM
Storage	External cassette tape, optional 5.25" floppy disk drive (Atari 1050)
Display	320×192 pixels (max), 40×24 text, 16 colours (ANTIC/GTIA)
Sound	POKEY: 4 voices, 8-bit mono
Dimensions	26.7 cm × 21.6 cm × 7.6 cm (10.5" × 8.5" × 3")
Weight	1.2 kg (2.6 lbs)
OS / Firmware	Atari OS Rev. 1, Atari BASIC Rev. B (in ROM)
Predecessor	Atari 400
Successor	Atari 800XL
Codename	Surely
Model no.	600XL

The Atari 600XL is a home computer released by Atari, Inc. in 1983 as the entry-level model of the XL series within the Atari 8-bit family. Designed as a budget-friendly companion to the Atari 800XL, the 600XL featured a smaller case, a membrane keyboard, and only 16 KB of RAM — half of what was needed to run many commercial programs of the era. Despite its limitations, the 600XL shared the same custom chipset and was fully expandable to 64 KB via the Atari 1064 memory module or third-party upgrades.

History

The 600XL was developed under the internal codename "Surely" as part of Atari's effort to replace the ageing Atari 400 and Atari 800 with a more cost-effective product line. Announced at the Summer Consumer Electronics Show (CES) in June 1983, the 600XL was positioned against the Commodore VIC-20 and Sinclair ZX Spectrum in the low-end market, while the 800XL targeted the Commodore 64.

At a retail price of US$199, the 600XL was significantly cheaper than the $299 800XL. However, its 16 KB RAM limitation proved to be a critical shortcoming — many Atari 8-bit programs required 48 KB or more to run, making the 600XL unable to use much of the existing software library without a memory upgrade.

Production of the 600XL was discontinued in 1984 after Jack Tramiel's acquisition of Atari, as the model was deemed unprofitable. Total production of both the 600XL and 800XL in 1983 was approximately 400,000 units combined.

Architecture and Processor

The 600XL is powered by the MOS Technology 6502C microprocessor (designated "SALLY" by Atari, part number C014806), running at:

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

The SALLY variant of the 6502 includes a HALT line that allows the ANTIC chip to pause the CPU during screen rendering for direct memory access (DMA), a feature unique to Atari's implementation.

The CPU is supported by Atari's custom chipset:

ANTIC (C012296) – Alphanumeric Television Interface Controller. A programmable co-processor that generates display lists and handles graphics modes independently of the CPU.
GTIA (C014805) – Graphics Television Interface Adapter. Manages colour output, player/missile graphics (sprites), and collision detection. An evolution of the earlier CTIA chip.
POKEY (C012294) – Pot Keyboard Integrated Circuit. Provides four-channel audio, keyboard scanning, serial I/O (SIO) control, paddle input, and random number generation.
PIA (6520) – Peripheral Interface Adapter. Handles parallel I/O for joystick ports and peripheral control lines.

This architecture is identical to the 800XL, giving the 600XL the same graphics, sound, and I/O capabilities despite its lower price point.

Memory

The Atari 600XL ships with:

16 KB RAM – provided by either two 4164 (64K×1) DRAM chips or a single 4416 (16K×4) DRAM chip, depending on the board revision.
24 KB ROM – split across two ROM ICs: a 16 KB OS ROM (Atari OS Rev. 1) and an 8 KB Atari BASIC Rev. B ROM.

The 16 KB RAM limitation is the 600XL's most significant drawback. Many commercial programs and games require a minimum of 48 KB to operate, rendering them incompatible without expansion. Atari addressed this with the Atari 1064 Memory Module, an external unit that plugged into the PBI port on the rear of the 600XL to expand RAM to 64 KB. Third-party upgrades also became available, including internal modifications that replaced or supplemented the existing DRAM chips with 4464 or 4164 ICs to achieve 64 KB.

Input/Output and Expansion

The 600XL provides the following ports and connectors:

Cartridge slot – standard Atari 8-bit cartridge port on top of the unit
SIO (Serial Input/Output) port – for daisy-chaining disk drives, cassette recorders, printers, modems, and other Atari peripherals
Parallel Bus Interface (PBI) – a 50-pin edge connector on the rear, providing direct access to the system bus for memory expansion and high-speed peripherals
2 × Joystick ports – DE-9 connectors compatible with Atari-standard joysticks and paddles
Composite video output – for connection to a monitor (active on some revisions)
RF modulator output – for connection to a television via the antenna input
Power input – barrel connector for external +5V DC power supply

The PBI is the 600XL's most notable expansion feature, providing a direct connection to the address bus, data bus, and control lines. This allowed peripherals like the Atari 1064 Memory Module to expand the system's capabilities beyond its base configuration. However, relatively few PBI peripherals were commercially produced.

Keyboard

The 600XL uses a membrane keyboard with a rubber dome design, similar in feel to the earlier Atari 400 but with individual key caps that provide better tactile feedback. The keyboard includes 62 keys with the standard Atari 8-bit layout, including function keys and the HELP, START, SELECT, OPTION, and RESET keys.

The keyboard is controlled by two CD4051 analogue multiplexer ICs (U22 and U23) which scan the key matrix in conjunction with the POKEY chip. Keyboard failures are commonly caused by degradation of these multiplexer ICs or contamination of the membrane contacts.

Display and Graphics

Graphics capabilities are identical to the Atari 800XL, handled by the ANTIC and GTIA chips:

Resolution: up to 320×192 pixels in bitmap mode
Text: 40 columns × 24 rows (Graphics Mode 0), with additional modes supporting 20 and 80 columns
Colours: up to 16 on screen simultaneously from a palette of 256 (16 hues × 16 luminance levels)
Player/Missile Graphics: 4 players and 4 missiles (hardware sprites), with automatic collision detection
Display List: programmable display architecture allowing mixed-mode screens and smooth scrolling

Sound

Audio is generated by the POKEY chip:

4 independent voices (channels), each with 8-bit frequency resolution
Programmable volume (4-bit), frequency, and distortion per channel
Channels can be linked in pairs for 16-bit frequency resolution
White noise generation for sound effects
High-pass filter capability when channels are linked

Power Supply

The 600XL uses the same external power supply as the 800XL, providing regulated +5V DC through a barrel connector. The original Atari power supply (Atari CO61982) is rated at +5V, 1.5A. The system draws approximately 800mA under normal operation.

Comparison with the Atari 800XL

**600XL vs 800XL Comparison**
Feature	Atari 600XL	Atari 800XL
RAM	16 KB	64 KB
Price (1983)	US$199	US$299
Keyboard	Membrane	Full-stroke mechanical
Case Size	Compact (26.7 × 21.6 cm)	Standard (40.6 × 24.1 cm)
PBI Port	Yes	Yes
CPU	6502C @ 1.79 MHz	6502C @ 1.79 MHz
Custom Chips	ANTIC / GTIA / POKEY	ANTIC / GTIA / POKEY
ROM	24 KB (OS + BASIC)	24 KB (OS + BASIC)
Cartridge Slot	Yes	Yes
SIO Port	Yes	Yes

Known Revisions

Several board revisions of the 600XL are documented:

NTSC Chelco Rev. 8A – manufactured by Chelco, common in North American units
PAL Rev A – standard European PAL version
NTSC Rev D – later North American revision

Board revisions may differ in the number and type of RAM chips used, capacitor placement, and minor circuit changes.

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