Systems

Jupiter Ace

The home computer that shipped with Forth instead of BASIC

Built in 1982 by the two engineers who had just designed the ZX Spectrum, the Jupiter Ace put Forth in ROM where every other home computer put BASIC — faster, more compact, and commercially fatal. Jupiter Cantab crashed in 1983; the machine outlived the company by years in the hands of its users' club.

jupiter-aceforthz80britishcambridgesinclair-diaspora?–1983

The Jupiter Ace was announced in the summer of 1982 and sold by mail order at £89.95 — the price included the machine, a power supply, leads for a television and a cassette recorder, a software catalogue and a manual.

It was built by Jupiter Cantab, formed by Richard Altwasser and Steven Vickers after they left Sinclair Research. Their own advertising made no secret of where they had come from: “leading computer designers Richard Altwasser and Steven Vickers… after playing the major role in creating the ZX Spectrum they formed Jupiter Cantab to develop their latest brainchild the Jupiter Ace.” Computer & Video Games introduced it in November 1982 as the work of “two ex-Sinclair engineers”.

One decision defines the machine.

Forth in ROM

Every other home computer of the period booted into BASIC. The Ace booted into Forth.

Jupiter Cantab’s case for it was a performance argument. Their advertisement — the same copy in Computer and Video Games for November 1982 and Your Computer that December and the following January — claimed Forth is “typically four times as compact and ten times as fast as BASIC”, and framed the choice as democratisation: “Before the Ace all personal computers used BASIC and Forth was only available to a privileged few.”

⚠ Both of those are the manufacturer’s marketing, not a measurement, and the library holds nothing that tests the four-times or ten-times figures. On a machine with 3K of RAM the compactness claim is at least the one that would matter most.

Forth is also a different idea about what a beginner’s language is. BASIC gives you a fixed vocabulary and asks you to arrange it. Forth gives you a mechanism for adding words to the language, so that a program is a vocabulary you built and the last word you define is the program. It is closer to how the machine works and closer to how a compiler works, and it rewards a reader who wants to know what is underneath.

What that means in practice is best shown by what the Ace does not have. A period guide, The Forth Bridge, tabulates BASIC keywords against their Forth equivalents, and the entries are startling to anyone expecting a language to come finished. Against SIN: “Not in FORTH, but the Ace manual gives a series definition of sine.” Against SQR, no equivalent either — instead a Newton-Raphson square root, written out as Forth words to be typed in:

: 2OVER ( f1, f2 - f1, f2, f1) 4 PICK 4 PICK ;
: 2SWAP ( f1, f2 - f2, f1) 4 ROLL 4 ROLL ;
: SQR   ( f - square root of f) 1. 10 0 DO 2OVER 2OVER F/ F+ .5 F* LOOP 2SWAP 2DROP ;

A machine sold to beginners shipped without a square root, on the understanding that you would define one — and that having defined it, you would own a language that had it. The same book puts the pitch better than the advertising did: Forth “enables him or her to begin from readily learnable words and then advance step by step to programs of greater complexity — building word on word.”

Almost nobody bought it.

Fast facts

  • Manufacturer: Jupiter Cantab, Cambridge
  • Designers: Richard Altwasser and Steven Vickers
  • Announced: summer 1982 · Launch price: £89.95, mail order only
  • CPU: Z80A at 3.25 MHz
  • Memory: 8K ROM, 3K RAM
  • Display: 24 × 32 characters, memory-mapped, flicker-free, monochrome, with user-definable high-resolution graphics
  • Language: Forth in ROM, with floating-point arithmetic
  • Also: programmable sound generator, fast cassette interface, full upper and lower case ASCII

What went wrong

The promised expansions did not arrive. A parallel printer interface was advertised “for around £20.00” and a 16K memory expansion “for around £30.00”; by 1983 the users’ club was writing that “the lack of promised add-ons from Jupiter Cantab indicates a cash-flow problem”. Third parties filled the gap instead — Stonechip and Essex Microelectronics made RAM packs, the club itself sold an adaptor kit that let ZX81 hardware be used on the Ace.

Richard Altwasser left Jupiter Cantab during 1983, Geoffrey Walker joining Vickers as co-director. The company crashed later the same year.

ACE magazine’s verdict, looking back in 1990, was blunt about the cause: the Ace was “the only home computer to sport Forth as its inbuilt language. This proved to be its downfall.” The same magazine filed Jupiter Cantab among the Cambridge companies as “the ill-fated splinter group from Sinclair Research”.

There was a second cause that the specification sheet does not show. A 1998 retrospective in CU Amiga remembered the build: a case of thin white plastic held together with plastic rivets, and a keyboard that was an extension of the main circuit board, its tracks shorted by conductive pads — “each key worked for about three months, and then a new keyboard had to be bought”. The Ace was made cheaply and it showed. Meanwhile “the Spectrum eventually appeared in big numbers, and blew the Jupiter Ace away”.

By the 1984-85 price war the remaining stock was going for £35.

The afterlife, which is the interesting part

The company died in 1983 and the machine did not.

Boldfield bought the bankrupt stock and kept selling — an Ace with a 16K RAM pack for £44 plus VAT against an original £89.95 and £34.95, and software cut from £7.95 to £3 — then assembled a list of add-ons and eventually commissioned new software for a computer whose manufacturer no longer existed.

The users’ club did more. Its newsletter, ACE User (later ACE User / Forth User), edited by John Noyce, ran a software catalogue that paid contributors 20% of sale price, quarterly and promptly; catalogued third-party RAM packs, sound boards and a colour board; sold its own ZX81 adaptor kit; and printed ROM addresses and Forth benchmarks sent in by readers. Its 1984 editorial states the position exactly: “Jupiter Cantab may have crashed in 1983, but the Ace lives on, indeed there has been a renewal of enthusiasm for it this year.”

It is a small, clear example of something this project cares about: a platform’s usable life is set by its documentation and its community, not by its manufacturer’s balance sheet. The Ace had 3K of RAM and no company, and people were still writing new software for it two years after the company failed.

A footnote on the ROM

Ian Logan, who had already disassembled Sinclair’s ZX80, ZX81 and Spectrum ROMs, got at the Ace’s ROM as well. The method is recorded in the club newsletter for December 1982: he cross-loaded it from an Ace to a Spectrum, the two machines’ cassette standards being identical.

Which is what you would expect. The people who designed the Ace had designed the Spectrum, and they used the tape format they already had.

See also

Not yet fact-checked. This entry was drafted by an AI and nobody has verified it. The dates, figures and technical details may be wrong. Use it to find your bearings, then confirm anything that matters against a primary source.