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1980s Computers Explanation of terms

The Jupiter Ace

Jupiter Ace


Jupiter Cantab (UK)



Date Launched

September 1982



Microprocessor type

Zilog Z80A @ 3.25 MHz

ROM size

8 kilobytes

Standard RAM

3 kilobytes
(1 KB available for programs)

Maximum RAM

49 kilobytes theoretically

Keyboard type

Rubber sheet, similar to Sinclair Spectrum's, with conductive rubber pads under each key which bridged tracks on the printed circuit board.

Supplied language

FORTH is a fully modular language and was tipped to become very popular in the 1980s, perhaps ousting BASIC as the 'standard' language. It is semi-compiled which means the Ace ran programs very quickly.
FORTH is also compact so the 1KB of memory was not too limiting.

Text resolution

32 x 24 characters

Graphics resolution

64 x 46 pixels

Colours available

Monochrome (white text on black background)

Example Screenshot

Jupiter Ace display
Pac-man on the Jupiter Ace. User-defined characters partly compensated for lack of true high resolution graphics.


Single channel through internal speaker

Cassette load speed

1500 baud

Dimensions (mm)
Weight (grams)

215 x 180 x 35

Special features

Used the FORTH programming language which was particularly suited to controlling external hardware.
The entire character set could be redefined.

Good points

Very fast program execution.
The only low-cost computer running FORTH.
Good steady screen display.

Bad points

As the only common implementation of FORTH there was little third-party software for the ACE.
The 3KB of RAM was rather small for late 1982. A version with 16 kilobytes internally was announced but never released. External memory packs of 16 kilobytes (for £30) or 32 kilobytes (for £50) were sold however.

How successful?

Unfortunately not very successful other than with a small number of enthusiasts interested in FORTH. Jupiter Cantab folded in November 1983.


If the specification above makes the Ace sound like a cross between the Sinclair ZX81 and ZX Spectrum this is no coincidence. Jupiter Cantab was formed by Richard Altwasser, who designed much of the hardware of the Sinclair Spectrum and later worked for Amstrad, and Steven Vickers who wrote the system software and manuals for the ZX81 and Spectrum.
The Jupiter Ace could in fact use some Sinclair peripherals, e.g. 16K RAM packs, just with the aid of a converter cable to allow for the different wiring of the edge connector.
The main advantages of FORTH, compact program size and rapid execution, were largely obviated by the fall in price of RAM and later by much faster processors and as a result FORTH never did replace BASIC.
Review from Electronics and Computing
Review from Personal Computer World

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