The background

My current job involves many hours of computing a day. I like my job, but I was never really fascinated about computers the way they work today. Everything involves high level programming nowadays and it is an easy potential way of getting money out of it. Computer hardware is out of the loop in my country as well as in many others. These huge companies just build all the hardware we need and we just consume it. I do not like the way it works but any computer hardware is so complex that it is prohibiting for a home brewer to build. Or is it not...?

Trying to find an answer to this question, I started searching for the history of computers, starting from electromechanical devices up to the modern computers. The complexity, the cost and the easiness of use of a computer makes discrete logic computers (electromechanical, vacuum tube, transistor, diode) unfeasible for the home brewer. On the other hand, by just looking at a modern motherboard one can clearly realize that it is just not possible to build a similar circuit in the home lab. To find the answer, I had to look on the computer designs of the 70's-90's. Many of these computers present easy usability at a fair amount of complexity. In other words, they may offer more for the complexity needed to make them.

Looking around on these machines, one cannot expect to run modern software on them. If you want to build a computer for multimedia purposes and fine graphics, this page is not for you. If you really want to explore the possibilities of a computer built with simple components for simple programming, more friendly user interface than microcontrollers and expandability for further development, you are in the right place. Probably the most successful of all designs in terms of usability and easiness of use, would be the IBM PC/PC-XT. It is mainly made of DIP chip packages and it can run DOS and all it's huge lot of applications that many of us were familiar with, at the past. The problem with PC was that it was more complex than some of the so called micro computers, or micros, at the time. In order to find which computer to build, one must think of the computer as a whole, not just the motherboard. The PC has a reasonable complexity motherboard but in order to operate correctly one must make at least a graphics card and a floppy disk controller, which are most of the times almost as complex as the motherboard itself. Apart from that, one must obtain the floppy drives compatible with it, which is just a pain to find one today. Not to mention the vintage floppy disks. Thus, the PC seems to be an unsuitable solution for the average home brewer.

Another solution could be one of these discrete logic CPUs combined with other logic chips to make a complete computer. These machines are more complex because they usually do not use embedded software at all and they try to do the software and the CPU job with logic gates. It seems that the answer to my question lies on these micro computers of the late 70's and early 80's. I wanted something that could be reproduced much easier and simpler than the discrete CPU and the PC, even if it does not run DOS. Deciding of which computer to build was not an easy task. I had to search through a vast amount of information to find one that is relatively easy to build and that it has the desired features mentioned above. I read some articles about computer history from mid 60's to mid 90's describing the technological and business efforts related to computer evolution. After examining carefully the features of each system, as well as the easiness of reproduction, the usefulness and the rareness of the components used, I initially decided to go for the Sinclair ZX80 system. So I built one!

Later on, I found that there exists a more advanced computer, which is the Jupiter ACE. This computer is more capable than the ZX80 and the complexity is not much more than the ZX80. For just about 5 more chips you have a computer with more memory, flicker free, integrated sound, more expansion ports and at almost the same board size. In fact, the ZX80 requires 5 or so more chips and the 8K ROM, to make it flicker free and compatible to the ZX81, so there is actually no added complexity on the Jupiter Ace.

Another great feature of the Jupiter ace is it's software. As far as I know it was the only microcomputer of that era that run the FORTH programming language and not the BASIC. FORTH was a very powerful language and it was considered well adapted to microcomputers with small memory and relatively low-performance processors. Forth allowed control structures to be nested to any level, limited only by available memory. Forth allowed implementation of machine code routines, if needed for a particular task. Forth also allowed recursive programming, if desired. On the downside, the usage of a data stack and the associated Reverse Polish notation were as unfamiliar as was structured programming.

Let's focus on the Jupiter Ace then!

One thing I wish to make clear is that this website is mainly dedicated to the building process of this computer. It includes all the details needed to build the computer from scratch, including the PCBs and the debugging of errors you may encounter. There are other wonderful sites on the internet that might provide you with tons of other useful info too.

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