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Remembering the Jupiter Ace

A brief look back at the computer which tried to make people switch from BASIC to FORTH.

Jupiter ACE Computer
Jupiter ACE (Photo by Dutra de Lacerda, alias Factor-H, Public Domain)

Ex-Sinclair Designers

Two of the Sinclair ZX Spectrum’s designers went on to form Jupiter Cantab, and develop a small low-cost 8-bit microcomputer called the Jupiter ACE.

In 1982, they released their creation, and advertised it in a similar way to Sinclair’s computers.

Jupiter ACE Advert EE Magazine November 1982
Bold claims in this advert for the Jupiter ACE, from November 1982. More

Sinclair Similarities

The ACE was comparable in size, appearance and hardware specification to the Sinclair ZX range.

It had the following things in common with the Sinclair ZX81:

  • 8 KB of ROM.
  • 1 KB of RAM.
  • Monochrome video output.
  • Z80 microprocessor clocked at 3.25 MHz.

The ACE was a little different by having an additional 2 KB of video RAM. That’s why it’s sometimes described as having 3 KB of RAM in standard form.

The ACE also had some things in common with the ZX Spectrum:

  • Moving-key keyboard (rather than a ZX81-style membrane one).
  • Sound generator.
  • Cassette interface which ran at 1500 bps.
Sinclair ZX81 Advert EE Magazine November 1981
One year earlier: An advert for the Sinclair ZX81, from November 1981. More

Unfortunately, like the ZX Spectrum, the keyboard was still of relatively poor quality, compared to the sorts of keyboard found on the Apple II or BBC Micro.

Sadly, the sound generator was fairly primitive. Rather than using a programmable sound chip like the Commodore 64 or BBC Micro, it just had a simple 1-bit output. That made it similar to the Spectrum or Apple II, by requiring CPU time for every pulse.

Unusual Language

The thing that made the ACE particularly interesting to me was its choice of built-in programming language — FORTH.

At the time, the majority of popular microcomputers were supplied with the BASIC programming language as standard. The use of FORTH was supposed to make the ACE ten times faster, and more memory-efficient.

Available at: Amazon.co.uk | Amazon.com

Limited Market Appeal

In reality, most home computers were used for gaming, and most games were written in machine code. That made the choice of language stored in ROM irrelevant — the hardware specification was the main thing that mattered. And that was an area where the ACE was not very strong.

With no colour graphics, a primitive sound generator similar to the Spectrum, and just 1K of RAM as standard, the ACE did not have much to offer the mass-market.

Programmer's Mug Z80 Chip


It’s a pity that the designers didn’t give the ACE colour, and perhaps a sound generator chip. That might have helped give it more appeal — although the price would have no doubt gone up a little.

Although I never owned or used a Jupiter ACE in the 1980s, its use of FORTH intrigued me.

The ACE seemed quite a quirky and unique machine. For that reason, I would like to get my hands on one at some point.

Do you have memories of using the Jupiter ACE?
Share your thoughts in the comments section below.

Related Articles

Memorable 1980s Home and Personal Computers

Remembering the Sinclair ZX81
Remembering the Sinclair ZX Spectrum
Remembering the BBC Micro
Remembering the Apple II

External Links

Story of the Jupiter Ace (The Register)
Jupiter Ace (Wikipedia)
Forth Programming Language (Wikipedia)

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