Acorn Atom
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The Acorn Atom is a
home computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...
made by
Acorn Computers Ltd Acorn Computers Ltd. was a British computer company established in Cambridge, England in 1978 by Hermann Hauser, Christopher Curry (businessman), Chris Curry and Andy Hopper. The company produced a number of computers during the 1980s with asso ...
from 1980 to 1982, when it was replaced by the
BBC Micro The BBC Microcomputer System, or BBC Micro, is a family of microcomputers developed and manufactured by Acorn Computers in the early 1980s as part of the BBC's Computer Literacy Project. Launched in December 1981, it was showcased across severa ...
. The BBC Micro began life as an upgrade to the Atom, originally known as the Proton. The Atom was a progression of the
MOS Technology 6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit computing, 8-bit microprocessor that was desi ...
-based machines that the company had been making from 1979. The Atom was a cut-down
Acorn System 3 The Acorn System was a series of modular microcomputer systems based on rack-mounted Eurocard (printed circuit board), Eurocards developed by Acorn Computers Ltd, Acorn Computers from 1979 to 1982, aimed primarily at industrial and laboratory use ...
without a disk drive but with an integral keyboard and cassette tape interface, sold in either kit or complete form. In 1980 it was priced between £120 in kit form, £170 () ready assembled, to over £200 for the fully expanded version with 12  KB of RAM and the floating-point extension ROM.


Hardware

The minimum Atom had 2 KB of RAM and 8 KB of
ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...
, with the maximum specification machine having 12 KB of each. An additional
floating-point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a Sign (mathematics), signed sequence of a fixed number of digits in some Radix, base) multiplied by an integer power of that ba ...
ROM was also available. The 2 KB of RAM was divided between 1 KB of Block Zero RAM (including the 256 bytes of " zero page") and 512 bytes for the screen (text mode) and only 512 bytes for programs (presumably in text mode, mode 0, and graphics not available), i.e. written in the
BASIC Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...
language. When expanded up to a total of 12 KB RAM, the split is 1 KB, 5 KB for programs, and up to 6 KB for the high-resolution graphics (the screen memory could be expanded independently from the lower part of the address space). If the high-resolution graphics were not required then up to 5½ KB of the upper memory could additionally be used for program storage. The first 1 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 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 KB but could be expanded to 6 KB. Since the MC6847 could only output at 60 Hz, meaning that the video could not be resolved on a large proportion of European TV sets, a 50 Hz
PAL Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
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.


Software

It had a built-in minor variation of Acorn System BASIC, a fast but idiosyncratic version of the
BASIC programming language Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * ''Basic'' (film), a 2003 film * Basic, on ...
developed by
Sophie Wilson Sophie Mary Wilson (born Roger Wilson; June 1957) is an English computer scientist, a co-designer of the instruction set for the ARM architecture. Wilson first designed a microcomputer during a break from studies at Selwyn College, Cambridge. ...
, which included indirection operators (similar to PEEK and POKE) for bytes and words (of 4 bytes each); the use of a semi-colon to separate statements on the same line of code (instead of the colon used by most if not all other versions of BASIC); and the option of labels rather than line numbers for GOTO and GOSUB commands. Assembly code could be included within a BASIC program, because the
BASIC interpreter A BASIC interpreter is an Interpreter (computing), interpreter that enables users to enter and run programs in the BASIC programming language, language and was, for the first part of the microcomputer era, the default Application software, applica ...
also contained an assembler for the 6502 assembly language which assembled the inline code during program execution and then executed it. This was unusual. String handling was based on arrays of characters. A byte vector to could be ensioned and then referred to with the string operator to be treated as a string. This sample program, adapted from ''Atomic Theory and Practice'', demonstrates some of Atom BASIC's peculiarities: 1 REM Encoder/Decoder 10 S=TOP; ?12=0 20 INPUT'"CODE NUMBER"T; REM Use code number to seed random number generator 30 !8=ABS(T) 40 INPUT'$S 50 FOR P=S TO S+LEN(S); REM For each character, if it is a letter add the next random number to it, modulo 26. 60 IF ?P<#41 GOTO 100 70 R=ABS(RND)%26 80 IF T<0 THEN R=26-R 90 ?P=(?P-#41+R)%26+#41 100 NEXT P 110 PRINT $S 120 GOTO 40 In late 1982, Acorn released an upgrade board for the Atom which allowed users to switch between Atom BASIC and the more advanced "BBC BASIC" used by the
BBC Micro The BBC Microcomputer System, or BBC Micro, is a family of microcomputers developed and manufactured by Acorn Computers in the early 1980s as part of the BBC's Computer Literacy Project. Launched in December 1981, it was showcased across severa ...
. The upgrade was purely to the programming language; the Atom's hardware capabilities remained unchanged, and hence, contrary to some pre-release beliefs, the BBC BASIC ROM did not allow Atom users to run commercial BBC Micro software, since nearly all of it took advantage of the BBC machine's much more advanced graphics and sound hardware and greater RAM capacity. Commercial BBC Micro cassettes could not have been loaded anyway, as they ran at a transfer rate of 1200 baud and the Atom's cassette interface only supported 300 baud. The following is the memory map for the Atom. Shaded areas indicate those present on the minimal system. The manual for the Atom was called Atomic Theory and Practice and was written by
David Johnson-Davies David Johnson-Davies is a British computer scientist and journalist, known for his contributions to the field of computing. Born in London, he studied experimental psychology in Cambridge and later joined Acorn Computers. As the founder and mana ...
, subsequently Managing Director of Acornsoft. The Acorn LAN, Econet, was first configured on the Atom.


Specifications

* CPU:
MOS Technology 6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit computing, 8-bit microprocessor that was desi ...
* Speed: 1 MHz * RAM: 2 KB, expandable to 12 KB *
ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...
: 8 KB, expandable to 12 KB with various Acorn and 3rd party ROMs * Sound: 1 channel, integral loudspeaker * Size: 381×241×64 mm * I/O Ports: Computer Users' Tape Standard ( CUTS) interface, TV connector,
Centronics Centronics Data Computer Corporation was an American manufacturer of computer printers, now remembered primarily for the parallel interface that bears its name, the Centronics connector. History Foundations Centronics began as a divisio ...
parallel printer * Storage: Kansas City standard audio cassette interface * Power: standard 2.1 mm power jack connector for 8 volts unregulated DC, providing 5 volts regulated inside the Atom The Acorn 8V power supply was only rated to 1.5 amps, which was not enough for an Atom with fully populated RAM sockets. The Atom's two internal LM7805 regulators (each regulating the +5V for a section of the digital logic independently) also got uncomfortably hot. Therefore, some Atom enthusiasts removed and bypassed the internal regulators and powered their Atoms from an external 5V regulated power supply. Three amps were typically needed for a fully populated Atom. There has never been a ''de facto'' standard for external 5V connections, but using the same 7-pin DIN connectors as the Atari 800XL allowed an Atari 5V linear power supply to drive an Atom, so long as the current was less than the Atari PSU rating (1 or 1.5 amps, depending on the model). These are now uncommon, but 5V wall-wart switch-mode power supplies capable of supplying several amps are a readily and cheaply available alternative.


Variants and applications

The Atom was incorporated into a "complete dedicated spreadsheet system" known as the Prophet by a company called Busicomputers, with the second edition of this product, the Prophet 2, consisting of a modified Atom, Ferguson 12-inch black-and-white television, and a Pearlcorder microcassette recorder, all housed in a "robust metal case". Powered by a single mains plug, the system was effectively a "turnkey" solution, emphasising the built-in spreadsheet as its primary function. Although regarded as worth considering as an "inexpensive way of obtaining a sound and reasonably well-presented spreadsheet system", being priced at £795 plus VAT, the use of cassette storage to reduce the system's cost was regarded as impacting its usability, with the slow data transfer rate causing waits of 30 minutes or more to save spreadsheet data and limiting the effective storage capacity of the microcassettes, whereas more expensive disk-based systems would be able to transfer similar volumes of data in a matter of seconds and store tens of spreadsheets on each disk. Regarded as "low-tech" later in 1983, the Prophet II was apparently being given away to participants of one- or two-day business-related training courses, these costing £600 and £700 respectively, with this initiative considered "a nice way of moving old stock". A subsequent model, the Prophet 3, featured a built-in floppy disk drive.


References


External links


Yet another computer museum - Acorn Atom







The complete Atom DVD

YouTube page totally dedicated to the Acorn Atom

Online museum of old computers

Javascript based Acorn Atom emulator
- containin

with th
AtomSoftwareArchive

A free, open source Acorn Atom emulator for Windows, Linux, OSX and Raspberry Pi
{{Acorn computers 6502-based home computers
Atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
Computer-related introductions in 1980 Computers designed in the United Kingdom 8-bit computers