The Atom was released in March 1980. The Atom is based on a System 3 in a new case
with keyboard. It was sold in kit (£120) or assembled (£170) form, a full expanded
model with 12K RAM and floating point ROM cost over £200. System computer eurocards
can be used to expand it via the 64-way ribbon cable attached to the expansion bus..
In addition to the standard Acorn Atom, Acorn made some OEM models in particular
the Busicomputers Prophet and the Hobbit which was made for a Dutch computer magazine.
Because the Atom is easily expandable and hardware was relatively simple, if expensive,
to make for yourself there are/were may Atoms with custom modifications.