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1980s Computers Explanation of terms

The Acorn Atom

Acorn Atom


Acorn Computers Ltd (UK)



Date Launched

March 1980


£140 as a kit
£174 ready assembled
Power supply £10 extra

Microprocessor type

MOSTEK 6502 @ 1 MHz

ROM size

8 kilobytes
Expandable to 16 KB

Standard RAM

2 kilobytes
(Divided up as 1KB for the system and BASIC variables, 0.5KB for the display and 0.5KB for BASIC programs.)

Maximum RAM

12 kilobytes on the main board.
35 KB with extra boards.

Keyboard type

Typewriter style

Supplied language

BASIC (fast-running but integer only) plus assembler.
Additional 4KB floating point BASIC ROM cost £23.

Text resolution

32 x 16

Graphics resolution

Nine different modes with resolutions from 64 x 48 to 256 x 192 pixels.
(All except the lowest resolution mode required extra RAM.)

Colours available

Monochrome (or 4).
The 6847 graphics chip in the Atom actually produced a colour output, but only in the American NTSC format. UK televisions using PAL saw the NTSC signal as monochrome. Hence there are conflicting reports of the number of colours available on the unexpanded Atom.
A module giving RGB colour output was available as an extra.

Example Screenshot

Atom display
Space Invaders on the Atom's monochrome display.


Single channel through internal speaker

Cassette load speed

300 baud

Dimensions (mm)
Weight (grams)

380 x 235 x 57
Not known

Special features

It was possible to add two extra ROM chips (e.g. to give floating point arithmetic) to sockets already on the board.

Good points

Good specification for the price in 1980.
Quite good version of BASIC.

Bad points

The standard 2 KB RAM was too small to use high resolution graphics and extra RAM cost £11.22 per kilobyte.

How successful?

Quite popular for an early computer, about 20,000 were sold.


The Acorn Atom was derived from the company's System 1, launched in April 1979, but with an integrated graphics chip to replace multiple components in the System 1.
The Atom was considerably better than its contemporary the Sinclair ZX80, having a moving key keyboard, high resolution graphics and a better BASIC, for a not too much higher price.
The Atom began the Acorn feature of expandability, continued with the BBC micro.
A slightly modified version of the Atom was also sold as the Busicomputers Prophet.

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