Editing Acorn Atom (section)

== Hardware ==

The minimum Atom had 2&nbsp;KB of [[Random-access memory|RAM]] and 8&nbsp;KB of [[Read-only memory|ROM]], with the maximum specification machine having 12&nbsp;KB of each.  An additional [[floating-point arithmetic|floating-point]] ROM was also available.  The 2&nbsp;KB of RAM was divided between 1&nbsp;KB of Block Zero RAM (including the 256 bytes of "[[MOS Technology 6502#Addressing|zero page]]") and 512 bytes for the screen (text mode) and only 512 bytes for programs<ref>{{Cite web|title=ATOM TECHNICAL MANUAL|url=https://www.acornatom.nl/atom_handleidingen/atap/atap02.html|access-date=2022-02-09|website=www.acornatom.nl}}</ref> (presumably in text mode, mode 0, and graphics not available), i.e. written in the [[BASIC]] language.  When expanded up to a total of 12&nbsp;KB RAM, the split is 1&nbsp;KB, 5&nbsp;KB for programs, and up to 6&nbsp;KB for the high-resolution graphics (the screen memory could be expanded independently from the lower part of the address space<ref>{{Cite web|title=EXPANDING THE ATOM|url=http://www.acornatom.nl/atom_handleidingen/atm/atm_06.htm|access-date=2022-02-09|website=www.acornatom.nl}}</ref>). If the high-resolution graphics were not required then up to 5½&nbsp;KB of the upper memory could additionally be used for program storage.  The first 1&nbsp;KB, i.e. Block Zero, was used by the CPU for stack storage, by the OS, and by the Atom BASIC for storage of the 27 variables.

It had an [[MC6847]] Video Display Generator (VDG) [[Video Display Controller|video chip]], allowing for both text and graphics modes. It could be connected to a TV or modified to output to a video monitor. Basic video memory was 1&nbsp;KB but could be expanded to 6&nbsp;KB. Since the MC6847 could only output at 60&nbsp;Hz, meaning that the video could not be resolved on a large proportion of European TV sets, a 50&nbsp;Hz [[PAL]] colour card was later made available. Six video modes were available, with resolutions from 64×64 in 4 colours, up to 256×192 in monochrome.  At the time, 256×192 was considered to be high resolution.

The case was designed by industrial designer [[Allen Boothroyd]] of Cambridge Product Design Ltd.