Acorn Atom       Credits to Chris
De Acorn Atoms van Chris Acorn computers site (at-

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The Atom was released in March 1980. The Atom is based on a System 3 in a new case with keyboard. System computer expansion cards can be used to expand it.

Manuals and documents

Here is a diagram of the lay-out of the Atom motherboard (from the Acorn Atom Review ) which shows the location of the ICs.

Atom motherboard layout


The Acorn Atom has a 1 MHz 6502 CPU. The minimum system has 2K RAM and 8K ROM. The 2K RAM is split 0.5K for program memory, 0.5K video RAM and 1K page zero, page zero is used by the OS, CPU stack and BASIC variables. The memory can be expanded to 12K RAM, split 5K for programs, 1K page zero and 6K for high resolution graphics (if hi resolution graphics are not used then an additional 5 ½K is available for programs.

The Acorn Atom has a Motorola MC6847 video chip which allows text (32X16 characters) or 2 colour graphics (upto 256 x 192 monochrome). It can be connected to a TV or, with modifications, a monitor. A PAL colour graphics card was also available. A 6522 VIA controls the serial and parallel ports. An INS8255 PPI drives the cassette interface and keyboard.

The basic Atom could be expanded by:

  • Expand the lower text space to 5K, in increments of 1K, this is used for BASIC programs.
  • Expand the Video Graphics RAM from 1K to 5K.
  • Install 4K Floating Point ROM
  • Install 4K Utility ROM, this can be any application.
  • Install 6522 VIA
  • Install a centronics printer port (requires 6522 VIA installed)
  • Install the 64-way connector for the Acorn bus and the bus buffers which allow external interface cards to be used with the Atom.
  • Add Eurocard extensions, Any of the Acorn Eurocards can be used with the Atom, including an Econet interface to network the Atom.
  • Other extension boards can be fittted to PL8

Note that when fully expanded the Atom power requirements can exceed that available from the Atom psu which will require uprating..

I bought my Atom second hand while living in Bedford in 1989. I also have a few Acornsoft programs, including the Indroductory Package. I have never seriously used the Atom.


  Acorn Atom

Acorn Atom and TV

 Acorn Atom plugged in to my TV and saying HELLO WORLD to show it is working. The power supply is an Acorn Atom mains power supply rated at 8V at 1.8A DC. This power supply is insufficient for a fully configured Atom and the Acorn Atom Technical recommends a regulated 5V DC power supply instead.


Acorn Atom front

Acorn Atom (front)

Acorn Atom right


Acorn Atom (right)

 Acorn Atom back

Acorn Atom (back)

 The back of the Acorn Atom shows the ports. On the basic Atom most of the ports are not fitted. The ports, from left to right, are:

  •  Acorn Expansion Bus (not fitted)
  • VIA Printer I/O (not fitted), with a suitable socket, a parallel printer can be conneted,
  • Video (not fitted), to drive a monitor
  • DC IN, 8V DC from Acorn Atom Power Supply
  • Tape I/O, a standard CUTS cassette interface
  • UHF O/P, TV output.

Acorn Atom case open

 Acorn Atom with case open

The top of the PCB has the keyboard, speaker and PL8 Extension Link.

 Acorn Atom motherboard

Acorn Atom motherboard

 This is a base configuration Atom, you can see the empty sockets for various expansions to be added. The motherboard is part no. 2002,000 issue 4.

A HiRes version of this picture is available HERE 


Serial Numbern/a
Motherboard part No.202,000 Issue 4
CPU Clock1MHz