A review of the Jupiter ACE.
Published in ELECTRONICS & COMPUTING, November 1982.


By Nigel Freestone

B.R. finally got me to Cambridge and the offices of Jupiter Cantab where I met Steven Vickers and Richard Altwasser who showed me their revolutionary new personal micro, the Jupiter ACE.

Steven and Richard made the break with Sinclair, where they worked on the ZX81 and Spectrum, to devote themselves full time to their new brainchild. The concept was a simple one, to offer the personal computer owner something better than what was already available in the price range (£89.95). Have they succeeded? With only minor reservations, some of which will disappear with time, I think they have.

Jupiter Ace


The revolution in this computer is in the language it offers — FORTH! FORTH has been around for a long time but this is the first micro to be developed especially to take advantage of FORTH's incredible speed, compact structure in memory and tremendous flexibility. (see FORTH COMPUTES OK E&CM September, October 1982). Steven and Richard wanted to get away from the deficiencies of BASIC but still keep the computer simple and easy for beginners to learn. FORTH fits the bill exactly.

Take the memory size for example, some may be critical of the provision of only 3K bytes of RAM, particularly when they learn that only 1K is available for user programs. Due to the very compact nature of FORTH code however, this is sufficient for much more powerful programs than 1K will support using BASIC.

The speed has to be seen to be believed. I have used FORTH before yet even I was surprised. A diagonal line, plotted pixel by pixel using a loop in graphics mode, does not "grow" towards the corner, it "appears" in its entirety!

If this is repeated inside another loop, first drawing the line and then erasing it, you might expect to see a white line flashing on and off. It doesn't, it turns grey! Don't worry if the line flickers, its just the T.V. scanning circuits are too slow to display it all before the computer rubs it out again!

If you know FORTH I hardly have to tell you about flexibility. In case you don't, let me say that the computer you get will understand 140 words contained in its dictionary ROM. A FORTH program is created by defining new words into the dictionary using the existing words in the definitions. Each new word building on whats gone before, literally extending the language as you program. Eventually entering a single word at the keyboard brings the program to life. We typed GAME and struggled to navigate our space ship through a meteorite storm. Simple, addictive, and very very fast. If you want a facility the machine does not have then you can add it to the dictionary, all the tools are there, its up to you how you use them.


Some excellent editing facilities have been added to the system.

VLIST displays all the words currently in the dictionary. This is like listing the whole program. EDIT displays the definition of a word on the screen and allows it to be edited. This display will almost certainly occupy several lines on the screen so the ability to move the cursor up and down, as well as left and right is especially useful. When the edited version is re-entered it forms a new definition on the top of the dictionary, meaning that the word now appears in the dictionary twice, once in the old version and once in the new. This is normal FORTH practice.

What is new and particularly powerful is the ability to REDEFINE a word. This updates the definition lower down the dictionary with the amendments just edited in. This is probably the only FORTH system with this very useful feature since it involves some very complex re-organisation of the FORTH dictionary. None-the-less it is completed instantaneously.

Data Structures

This implementation of FORTH allows the following data types to be used. 16 bit integers, 32 bit double integers, Floating point numbers to 6 digits with exponents from -64 to +62 and FORTH 79 standard string literals. String variables, arrays and matrices can all be defined as required.


Several features of the ACE show signs of its designers' recent associations with SINCLAIR. The general appearance reminds one of the ZX80, although at 215mm wide, 180mm deep and 35mm high, it is probably a little bigger. [Actually it is almost exactly the same size.]

The case is vacuum formed white Styrene, which didn't look very strong but proved capable of taking some quite rough treatment.

The keyboard is similar to the Spectrum. The keys are moulded in silicone rubber as a single sheet with the legends heat treated to that they never come off. The contact is made by an electrically conducting fubber [sic] bead underneath the key bridging two tracks on the surface of the printed circuit board. It remains to be seen how this is affected by dirt and moisture. Since the PCB forms a vital part of the keyboard assembly, it cannot be unplugged. Anyone wishing to replace it with a "real" keyboard will have to solder the keyboard leads directly on the PCB.

Both upper and lower case letters (with real descenders) are available (using SHIFT), the symbols being entered by using symbol shift. Eight pre-defined graphics characters are available on the numeric keys. All characters are available from the keyboard. Cursor moving arrows, Graphics mode, Delete and Caps Lock are all on the numeric keys using Shift. There is auto repeat on all keys. Since FORTH allows the user to define his own keywords, all the keywords on the Sinclairs are notable by their absence.

The display is sharp and free from snow. It displays 24 lines of 32 characters each on T.V. set tuned to Channel 36.


Sound on the ACE is similar to Spectrum sound, even the same command is used. BEEP expects two values, one for pitch and one for duration. The duration is in milliseconds but the pitch is more complicated. The value sets the period of the frequency produced and is in units of eight micro seconds. While the pitch is probably unimportant when playing games, those who wish to play serious music may find the necessary calculations rather tedious if not actually difficult. A conversion table in the manual will show the necessary values for a range of common notes. Only one note can be produced at a time and there is no control over the volume which is only just about adequate. No one knew whether the signal is available at any of the external connections for amplification.

No Colour (yet)

Colour is not available. Steven and Richard argue that the majority of T.V.s are still black and white and most personal computers are used with black and white portables anyway. I think many people will be disappointed at the lack of colour, but I can tell you that the smaller of the two edge connectors on the back of the machine is ready to take the colour adaptor due to be available early next year for around £30.

On the Inside

Internally the PCB is good quality and well laid out. Several of the bigger chips are in sockets although none of these are specially designed for the ACE. Six connectors lead to the outside world. The colour encoder connection has already been mentioned, the other edge connector at the back carries full address and data busses along with power supplies and control signals from the CPU. The 9V 800mA separate power supply plugs into the left hand side. This is adequate to power the computer and some extra expansion boards such as the planned 16K RAM pack, but those extending their machine more than this may require a more powerful PSU. Three sockets on the right hand side connect to the T.V. aerial and the cassette recorder Mic and Ear sockets. Leads for these come with the machine.

Cassette Interface

SAVE, LOAD and VERIFY are all available and seem to work well. SAVE copies the whole of the Dictionary in RAM to tape at 1500 baud. The word following SAVE is used as the filename and may be up to ten characters long. A tone is recorded before the start of the data to allow the automatic level control on the recorder to settle to the correct level before the data starts.

VERIFY allows the contents of memory and the tape to be compared.

LOAD searches through the tape until the named file is found, then it reads it onto the top of the dictionary already in memory. This allows the user to save small "subroutines", and the[n] LOAD them one after another into memory before loading or writing the main program that uses them. Once the program is complete the whole dictionary can be saved again. Alternatively several completely separate programs can be loaded into memory at the same time and used one after the other, e.g. a series of games or a financial program and a calculator.

Users may have some problems with LOADing programs from tape because there is no indication that anything much is happening. When a filename is found on the tape it is displayed on the screen. This makes it possible to obtain a catalog of the files on the tape by entering LOAD without a filename. But because there is no visual or audible indication that any data has been detected, users will never be quite sure whether the tape is blank, the computer has found a long file which it is reading to get past, or the volume control setting is not high enough for it to register the signal. Once the correct level has been found, this should cease to be a problem.

SAVE BYTES allows a section of memory to be copied to tape. This will probably be used most often for saving user defined graphics characters, which leads me on to...


The ACE offers two types of graphics, User defined and "Chunky".

Every character available on the machine has its dot pattern stored in RAM! Both the normal and inverse video varieties being available. The characters are set up in RAM when the machine is first turned on, but thereafter may be redefined at any time. So if you want to write on the screen upside down, or label the vertical axis of a graph by writing sideways up the screen, you can. If only a small number of special characters are required, redefine some of those you are not using, say the inverse video ones, or you can redefine them all. Once they are defined SAVE them on tape and LOAD them in when required.

The chunky graphics allow you to PLOT individual pixels. The screen displays 32 characters on each of 24 lines. The last line is reserved as the keyboard input buffer so plotting is only possible on the top 23 lines. Each character is divided onto four pixels giving a plotting resolution of 64 by 46.

The PLOT command requires three parameters. Two specify the X and Y co-ordinates of the pixel concerned. The third is the plotting mode.
Mode 0.UnplotMake it Black
1.PlotMake it White
2.MoveUpdates the last plot co-ordinates
3.ChangeIf its on, turns it off etc.

The plotting resolution is not high but probably adequate when the user defined characters and the speed of the machine are taken into account.


I didn't see a copy of the manual because they were still at the printers. Steven was responsible for the Spectrum manual however, and I expect this one to be up to the same standard.


The ACE is a great little machine. It will become better still with the advent of the 16K RAM pack, the colour card and the printer interface planned for next year. Steven and Richard also have various software packages in the pipeline. These include Floating point Trig functions, turtle graphics, Z80 Assembler and Games.

Even without these enhancements the ACE, with its revolutionary FORTH and incredible speed and flexibility, will make a great first (or second) machine for anyone.¨


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