HAPPENINGS

THE OFFICIAL BLOG OF HARRISBURG ACADEMY

Ancient Computers, Part 3

In part 2 of this series, I left off sharing that I was learning to program a Z80 Starter computer in its native machine language — and I reported that the computer still works! It has evolved quite a bit, although it never did become the Altair-like micro-computer I had planned to create.

Not long after the Z80 Starter computer, I was employed as a part-time electronics technician at a local electronics company while in college at Penn State, working on my electrical engineering degree. I was troubleshooting and repairing all manners of electronic terminals that were used on the mini-computers and mainframes of the world.

One of my colleagues purchased a complete and functioning Cromemco Z-2D micro-computer — an Altair-like machine in function. Lacking the space in his tiny apartment, he set it up at work. For the cost of a floppy disk, roughly $2, he let me use it off-hours for programming in FORTRAN or Z80 machine language. Being able to touch and work with a real micro-computer with a terminal, a printer, and floppy disks for storage convinced me even more that I had to have one for myself — but the $4,000 price tag of the Cromemco was way too steep.

Others had built their own micro-computers, so why not me? Certainly, I now possessed the background to accomplish such a project, and I got started piecing together the parts I would need: A backplane with several slots for plug-in boards using the current and popular S-100 technology (the same as the original Altair, also used by the Cromemco); a Z80 CPU processor card; a memory board; a terminal board that worked with a surplus keyboard and video monitor; a disk controller board along with two floppy disk drives; and a home-built box to put it all in. I purchased a legal, licensed copy of CP/M from Digital Research (the “Operating System” that we know of today as “Windows”), and after a few months, the machine was finished and working. Total cost, if I remember correctly, was about $800. From this point on, I was learning several programming languages each year: BASIC, Pascal, and C to name just a few — all made possible by a functional micro-computer in my home.

So, in a round-about way, I did arrive at the goal I set for myself so many years earlier. I went on to finish my BSEE degree, and prior to my arrival at the Academy, I worked at a number of jobs that built on my experiences with reaching my micro-computer goal: chief engineer designing computers for industrial applications, designing computer networks and systems for all manner of the commercial segment, and working as a computer systems engineer constructing servers on fiber optic networks.

During this time, a collection of “ancient computers” has been growing in my workshop at home, including a Mark-8 replica (the original Mark-8 pre-dates the Altair), a 68000 Educational Trainer, and a very early IBM PC clone. All still work, and all had something to do with shaping my experiences, so when it came for the possibility of employment here at Harrisburg Academy, I was confident that I could do everything being asked, including teaching programming.

Although my experiences with many different computer systems and programming languages went many ways, and some ancient computers remained just that, my S-100 computer did not sit still. Today, there is a very lively group of hobbyists (we used to call ourselves “hackers” until that word took on its negative connotation!) around the world who continue to work on S-100 computers, even developing new hardware and software for them. I am one of that group. In the past several years, I have designed and sold a new board for the system, and wrote a complete program of nearly 5,000 lines of Z80 machine code that is used by the community. My S-100 computer has evolved enormously, and several years ago, I built a second one. I close this series with a few photos of some of my ancient computers. Some are not ancient after all! If you have further interest in my ancient computers, please be in contact.

Learn more about Harrisburg Academy on our school website.

My second S-100 computer, built three years ago as a hardware and software development system.

My enormously evolved original S-100 system; keyboard and mini-floppy drives are original.

My Z80 Starter computer in a case on top, Mark-8 replica with green front panel, 68000 Educational Trainer in foreground, and Heathkit H-19 terminal on the right. All operate normally.