back to article The Jupiter Ace: 40 years on

The Basic programming language, although present in many different dialects, was the lingua franca of early 1980s home computers. One machine dared to be different: Jupiter Cantab's Jupiter Ace, a small unit that spoke Forth. It first went on sale decades ago. Forth was conceived by Charles Moore, a computer scientist employed …


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  1. Andus McCoatover

    Takes me back..

    I always wanted one, but got a book on Forth, describing how to write it.

    Over a sleepless weekend, I managed to get it running on a CP/M machine (8085). A lot of Forth is written in Forth, only had to write the primitives in assembler, so it wasn't too big a job - whole thing easily fitted on a 5.25" floppy, including CP/M itself.

  2. Anonymous Coward
    Thumb Up






    1. Anonymous Coward
      Anonymous Coward

      Me too. It's funny, but with hindsight just think what you could achieve.

      I wouldn't bother with buying a machine at all but would be on the phone to Motorola blagging some 6089 samples and building something from scratch. As these stories demonstrate, you really could put something together on the kitchen table and have yourself a functional machine in a reasonable about of time.

      (It would also be a good opportunity to get the open source ball rolling earlier. Not sure how the logistics of that would have worked though. Perhaps persuading universities to host public dial-up servers?)

    2. Anonymous Coward




      Where the hell did they go?

  3. The Starglider


    "Ten times faster despite running on the same Z80A processor that was found in the Spectrum and being clocked to 3.25MHz, eight per cent lower than the Spectrum's 3.5GHz."

    You know, I'm pretty sure that 3.25Mhz is more than 8% slower than 3.5Ghz, but I don't remember my Speccy being faster than my PC! ;-)

    1. mrmond

      Re: Really???

      It wasn't talking about the hardware being faster but the programs when running.

      Forth executes much faster than Basic, just as machine code runs much faster than either on the SAME machine.

      1. The Starglider

        Re: Really???

        I think you're missing the glaring error I was making a joke out of in the article!

      2. VinceH

        Re: Really???

        "It wasn't talking about the hardware being faster but the programs when running."

        Take a closer look at the units used.

      3. Anonymous Coward
        Anonymous Coward

        Re: Really???

        Indeed... I really didn't think you could overclock a Z80 into the gigahertz like that.

        Those things really were cooking!

  4. Geoff Campbell Silver badge

    Best investment I ever made.

    Bought one some time in the '90s for a tenner, sold it on eBay recently for something over £300. Better return than any of my supposed pension investments.


    1. vic 4
      Thumb Up

      Re: Best investment I ever made.

      You beat me to it. I bought a bunch second hand (along with sinclairs, dragons, vic20 etc). First tiem I sold some I was getting loads of emails every day asking to close the auction and sell immediatly (before buy now came along), lowest was around £225, highest one went for £650 but that was in near new condition, had a ram pack + a bunch of add on circuit boards and parts. I Keep watching the classifields but never seen one for many years.

      Only got a zx81 and sinclair printer left :-( My new collection is aging sun and sgi boxes, sun pizza boxes make great foot rests.

      1. Andus McCoatover

        Re: Best investment I ever made.

        Lesson to be learned! Buy Nokia Lumias!!! Lovely Jubbly, be worth a mint in a Flop^Wfew years time.

    2. VinceH

      Re: Best investment I ever made.

      "Bought one some time in the '90s for a tenner, sold it on eBay recently for something over £300. "

      I get seriously annoyed with people who have done that.


      Because I had quite a few of the old home computers in the early 90s, and eventually either dumped them, gave them away, or sold them for what I thought they were worth at the time - ie next to nothing.


      1. Geoff Campbell Silver badge

        Re: Best investment I ever made.

        Well, you can't really blame us for your lack of foresight :-)

        I was buying up a whole bunch of different stuff, as I wanted to have them to play with later on in life. Got all sorts of machines, mostly for a tenner - to the point where the TLA GST was coined on some systems, for "Geoff Standard Tenner" as a unit of currency.

        Twenty years on, I realised there was no point in having a loft full of machines I wasn't getting the time to even look at, and decided to sell them on to people with more spare time and enthusiasm than I had. I was quite surprised by what some of them fetched.


      2. Anonymous Coward
        Anonymous Coward

        Re: Best investment I ever made.

        me too - had dragons, color computers, IBM PC-XT, Jupiter Ace and god knows what else - sold off for a fiver each in the late 80s, when I got a 386 running windows 3.0. the money I threw away....

  5. Anonymous Coward
    Anonymous Coward

    I do enjoy reading these mini epitaphs for the British computing industry. I am wondering if we are going to be treated to one on the Oric 1 in due course? ISTR that effort had the obligatory interesting Cambridge-based back story and stellar demise. Oh, and it came with Basic and Forth.

    1. david 63

      It came out of Tangerine.

      I worked closely with Barry Muncaster and his team. He made his money making meters for taxis. I used to write articles and the problem page for Oric Owner.

      I also helped debug the version 1 ROM (actually and eprom in the early versions)

      Shame the 6502 faded away. It had brilliant instruction set.

      1. . 3

        Re: It came out of Tangerine.

        Excellent stuff! I had an Oric at primary school age. I remember my Dad coming home one day with a copy of the v1.1 ROM burned onto a couple of EPROMs. I guess someone at work must have had a new Atmos and let him have a copy of the ROM image somehow. It absolutely transformed the machine. I took the old EPROMs to school subsequently to show to the awe of the children (and confoundment of my teacher). "You can see the actual microchip through the little window!"

        The 6502 and its beefed up successors are still very much alive inside of various ASICs. I bought a little photo frame a while ago which contains a very standard 6502 augmented with JPEG decoder hardware, SPI flash and USB interface.

      2. Thomas 4


        Don't be too downhearted for the 6502 will actually make a comeback in the distant future, serving as the CPU of Bending units.

        (It's in the episode of Futurama where Fry is looking inside cans of Slurm with an X-Ray. He shines it on Bender's head and clear as day, there's a 6502 chip in there. I always wondered about the reference.)

        1. Tom 7

          Re: @david

          the 6502 lives in glorious technicolour:

      3. Dave Lawton

        Re: It came out of Tangerine.

        Didn't really fade away, it metamorphosed into the ARM 1, with the help of a few brilliant engineers.

  6. david 63

    I loved my ACE. Never made it do anything useful but I still loved it.

  7. Julian 4

    Childhood 2.0

    The biggest achievement for the Jupiter Ace was that everyone wanted one once the company had gone bust and I missed my chance too. The nearest I could get was the Nottingham Microcomputer Club's single Jupiter Ace which would be out on permanent loan with a waiting period as long as a Sinclair delivery schedule, so when I finally got the chance I spent a happy homework-free couple of weeks ploughing through the manual; cramming my head full of its Forthy goodness and mind-blowing concepts.

    A brilliantly clever machine flawed only by its tame monochrome graphics and glitchy keyboard driver (the rubber keyboard is actually fine, it's the firmware that's at fault).

    Aaaaah, and it says it all that Ace's are practically just as unobtainable now; if only there was a similar 8-bit Forth computer you could buy today; we could all reclaim our childhoods ;-)

    1. Gaius

      Re: Childhood 2.0

      Have you seen the FIGnition?

    2. Vic

      Re: Childhood 2.0

      > if only there was a similar 8-bit Forth computer you could buy today

      Well, not exactly 8-bit, but you can do 16.

      My customer gave me a couple of MSP430 Launchpads this week. Apparently[1], they can run Forth. And they're four quid a pop.


      [1] I've not actually had a chance to turn on one yet...

  8. Neil Barnes Silver badge

    I saw a complete Ace only once

    But after the company went bust - long after, perhaps 1985 - I obtained from somewhere a handful of Jupiter motherboards, unpopulated, and built a couple up from scratch. I already knew Forth from a Tangerine system (and incidentally a Z80 CP/M system which I used as a front end for the Tangerine) so talking to it was no problem.

    There must be dozens of us old fogies on El Reg who grew up when if you wanted a computer, you sat down and designed the damn thing, built it, and debugged it... or if you had a basic kit, you designed all the add-ons like video cards and storage.

    More of these old memories, please - I'm waiting for your retro-review of the Amstrad 1512, the computer that the Open University guaranteed would last my entire degree course! (Er, it didn't.)

    (So here I am today having just spent a month replacing an existing Z80 system with a PIC!)

    1. Andus McCoatover

      Re: I saw a complete Ace only once

      Being an "old fogey" - proud of it, too, blowing fuses in proms in 44-bit wide microcode to make a spectrum analyser (Nicolet 440). Youth of today. Don't know they're born.

      (Finishes pint, gets on bike, rides 100 miles to lick t' motorway clean.)


  9. Mage Silver badge


    It was great for writing programs to test stuff. I forget what we connected it to. They should have had a DIN module version from the beginning with an expansion I/O backplane. That would have been a niche market but successful.

    I gave my personal one away circa 1973. The Pac-Man game ran well. Being able to use any number base was "unusual". Base 32 anyone?

    Forth and of course HP RPN calculators are a bit Marmite.

    1. Mage Silver badge

      Re: Test

      Late 1983 ... not 73 (when do we get an edit feature?)

      1. Anonymous Coward
        Anonymous Coward

        Re: when do we get an edit feature?

        it's called preview

    2. Andus McCoatover

      Heh! Marmite...You either love it or hate it!

      Still got an early HP RPN calculator. HP35. Gotta find out how to stick some new batteries in it, and hook up a charger of sorts.

      Frikking hell, just found out the thing's 40 years old!!!! Definitely gonna work on firing that baby up. If my Sinclair Scientific still works, I've no reason to suspect this baby won't!

      1. Neil Barnes Silver badge

        Re: Heh! Marmite...You either love it or hate it!

        Still using my 1985 HP11C. Was irritated last month as I had to change the batteries for the first time...

  10. Richard Scratcher

    I still have mine

    Or rather, my brother's. We rehoused it in a metal box with a new keyboard and installed it under the telly to manage our video tape library. It worked well unless it got unplugged and we had forgotten to back things up to tape. But that happened rarely...maybe once a week.

    1. Vic

      Re: I still have mine

      I've still got mine, too. And it works.

      It was not quite my first foray into Forth, but probably took more pounding than the Tiny Forth I started with.

      And 30 years later, I'm still writing Forth. And getting paid for it these days :-)


  11. Bod


    Looked cool in WH Smiths next to the others but I could never work out how to make it flash and scroll rude words in Forth.

  12. David Given

    Get one

    If you know a little Forth, it's worth grabbing an emulator (there's a whole bunch on and giving it a go. It's a humbling experience. Where a ZX81 feels like a toy, an Ace with 3kB feels like a real computer --- something you can actually genuinely write useful programs in. Their Forth, extended to allow words to be redefined, provides one of the most minimalist yet real development environments I've ever seen, providing both low level and high level features at the same time.

    The implementation was a work of art, too, using all kinds of strange Z80 features to achieve maximum code density. There's a disassembly here: If you want a (now rather old fashioned, but still useful) Z80 Forth implementation, you could do a lot worse.

    And if you don't know any Forth, LEARN SOME. It's pretty much useless in real life, but knowing Forth will make you a much better programmer in other languages. And it is the go-to language for really low-end embedded devices.

    1. Vic

      Re: Get one

      > extended to allow words to be redefined

      Indeed. You can use that stunt to write recursive words too - although that's not necessarily a good idea if you've only got 3KB of RAM...


  13. Anonymous Coward
    Anonymous Coward

    Vickers' ZX Spectrum manual remains one of the best computer books I've read, and probably the one that taught me the most.

  14. Dazed and Confused

    Forth was a lot of fun.

    I thought of buying one of these because it ran Forth.

    I'd been introduced to Forth by a lecturer at college who thought I'd find it interesting after I'd written a program to do framework stress analysis on a programmable calculator. He had it running on an Excidy Sorcerer and mate with rich parents had one. The Excidy had half its character generator in RAM, so you could get heady high res graphics (640x240ish I think) by carefully redefining characters and so I quickly wrote a copy of Space Invaders in Forth.

    Ah... that takes me back.

    Had my HP85 out yesterday, the eldest is off school and though it was time for him to have a chance to write some software.

  15. andy gibson

    Forth Vs Machine Code

    FORTH may have been great at being faster than BASIC (if you didn't factor in all the extra time needed to learn Forth!), but any computer geek at the time would have been looking towards machine code.

    The outstanding "Spectrum ROM disassembly" and David Webb's "Supercharge Your Spectrum" were the two treasured books to have & inspire you and are still on my bookshelf today.

    1. Furbian
      Thumb Up

      Re: Forth Vs Machine Code

      Indeed Sir, which is why I learnt Z80 Assembler...

      ... did part of my O-Level Computer Studies project in it....

      ... learnt 68000 Assembler on the back of that knowledge, but never quite wrote an Atari ST, or Commodore Amiga Program...

      ... which also meant that when I was working on a financial company's DEC-VAX system (early 2000's I kid you not) that had Macro 32 Assembler that needed fixing, I could...

      ... and I now (part time) tutor ARM Assembler at the University of ...

      Oh The ACE? Bought a pair of books on Forth (Language Library's Fundamentals and Techniques, I can see them in my bookshelf!), but never bought one in the end. Shame, would have been an interesting experience. However I did use Forth, beats me what it was on.

      Anyone remember 'Fifth' by some chap for the ZX Spectrum, was that related in anyway?

      1. JQW

        Re: Forth Vs Machine Code

        Fifth had nothing to do with Forth. Instead it was a BASIC extension that used REM statements to host new commands. As Fifth was for writing games, the extensions were mainly for handling sprites and sound effects.

  16. ForthIsNotDead
    Thumb Up

    All this talk of Forth...

    ...means I am having a very good day today!

    <--- check the handle :-)

  17. ForthIsNotDead

    Some Forth:

    A loop that counts from 0 to 99:

    : 0to99 100 0 DO I . LOOP ;

    Simple, eh?

    1. Chemist

      Re: Some Forth:

      I'm more impressed by NEXT in 6809 assembler - 4 bytes !

      1. Steve Knox

        Re: Some Forth:

        Shurely NEXT is 4 bytes in any 8-bit code...?

        1. Chemist

          Re: Some Forth:

          No, most 8 bit forths need to JSR which , of course, can be a variable length routine depending on processsor. With the 6809 the actual code to implement NEXT is 4 bytes and can be put in-line saving the sub-routine call at the expense of slightly longer code

          LDX 0,Y++

          JMP [0,X]

          1. Chemist

            Re: Some Forth:

            Sorry, should qualify, that's for indirect threaded code as per most early 8-bit Forths

            1. David Given

              Re: Some Forth:

              I think I managed to get NEXT down to one instruction on the ARM --- ldr pc, [ip, #4]!, maybe? It's been a very long time.

              I was deeply impressed by Forth, from its design to its philosophy to the utterly minimalist implementations. Can I actually do anything useful with it? Can I hell. I'm far too fond of things like type checking, and variables, and syntax that can be checked at compile time, and little stuff like that.

              An HLL that compiles into Forth would be a very nice thing to have, but producing good code from Algol-alikes like C would be hard because of differing stack semantics. JVM bytecode, perhaps --- it's already stack-based, after all...

        2. Steve Knox

          4E 45 58 54

          4 bytes. (Mostly) platform independent.

    2. This post has been deleted by its author

  18. Anonymous Coward

    30 years, and yet that damn Robot still hasn't brought them home....

    30 years, and yet that damn Robot still hasn't brought them home....

    (yes, Jupiter ACE not Jupiter II, but....)

  19. arrbee


    I think I may be getting old... I remember writing one of my first ever programs in Forth in, err, 1976

    - it was for something called an isodensitracer [ well, something like that ] which was used to measure images on photographic glass plates. IIRC it was using some kind of Honeywell minicomputer.

  20. Steve Knox

    Page 3 Pics


    First one typical of any 80s' computer ad - had to include a chess picture.

    Other two typical of tabloids -- pics of the model topless.

  21. erather

    Thanks for the nice article.

    And thanks for mentioning me! I'm happy to say that Forth is alive and well, though still a minority language. Its primary success has been in embedded systems, although commercial and public domain/GPL versions exist for virtually all platforms. Like other computer technologies, Forth has come a long way in the last 30 years. An ANSI/ISO Standard was adopted in 1994 that enabled vastly more efficient implementation strategies, yielding powerful and fast systems that compete with C in performance without losing the compactness and interactive style that was so attractive on the Ace. More information (including links to current system providers) may be found at

  22. J. Simon van der Walt

    Oh yes, them were the days

    My flatmate had one, let me use it. Loads of fun, somewhere I've still got Forth code written out by hand for a drum machine: actually, the Forth stuff was just to programme the rhythms, there was some sort of serial interface I seem to recall, which I used to drive some homemade analog drum sounds.

    Speed: yeah, I remember writing a ball-bouncing-around-the-screen program. Couldn't understand where I had gone wrong: no ball?!? Then I realised the thing was going *so fast* the ball didn't have time to display!

    And of course, the added joy of working through Leo Brodie's 'Starting Forth', the most entertaining programming book I've ever read :)

  23. Liam Proven Silver badge

    > if only there was a similar 8-bit Forth computer

    Well, some enterprising soul could port ColorForth to the Raspberry Pi - that'd be close. Should be unbelievably quick and the absence of 3D drivers, video decode and so on would not be a problem - in this case, the language /is/ the OS.

    Don't bother trying if you suffer from daltonism, though...

  24. Christian Berger


    I had an ZX80 with the ZX81 ROM, as well as a TI99/4A. And I have to tell you, the ZX80 was _way_ faster. It's mind-boggling how fast the Ace must have been then.

  25. Anonymous Coward
    Anonymous Coward

    Nice, but was having Forth *onboard* sufficient selling point for otherwise generic hybrid?

    I've heard about the Jupiter Ace before, and I'm certainly not criticising its brave (and interesting) decision to go with something different than the over-ubiquitous and bad-habit-forming BASIC- quite the opposite.

    However, the fact that Forth was its unique selling point- to the extent that even in discussions today it seems to overshadow the spec of the hardware itself- seems somewhat unusual when you consider that implementations of Forth were- or could have been made- available for many computers that used BASIC. Granted, it might have been a pain- and a waste of RAM- to load it from tape, but surely it would have been possible to implement it as a cartridge (or a rampack-like ROM-based add-on for machines like the ZX81).

    If we disregard the language for a second, the Jupiter Ace was somewhere between the already-established ZX81 and ZX Spectrum in terms of spec, and the market was already sagging under a ludicrous number of 8-bit home computers (my Dad's "Your Computer" magazines from around 1982-84 seemed to have reviews of between 1 and 3 new- and mutually incompatible- machines every month).

    It might have been a decent machine for the money, but was there sufficient space in the market for it? And perhaps this is why it failed. Having Forth *onboard* (rather than as an add-on) might have been good, but perhaps- when people came to plonking down their cash- people realised that it was simply an aspect- and differentiator- of the machine, which was otherwise somewhere between the better-supported ZX81 and Spectrum.

    I appreciate that Altwasser and Vickers (quite understandably) wanted to make money for themselves, rather than Sinclair, and that building a machine around Forth probably got more attention than selling a ROM-pack for the ZX81, but it was also a higher-risk choice.

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