In the days before computers usually used off-the-shelf CPU chips, people who needed a CPU often used something called “bitslice.” The idea was to have a building block chip that needed some surrounding logic and could cascade with other identical building block chips to form a CPU of any bit width that could do whatever you wanted to do. It was still harder than using a CPU chip, but not as hard as rolling your own CPU from scratch. [Usagi Electric] has a Centurion, which is a 1980s-vintage minicomputer based on a bitslice processor. He wanted to use it to write assembly language programs targeting the same system (or an identical one). You can see the video below.

Truthfully, unless you have a Centurion yourself, the details of this are probably not interesting. But if you have wondered what it was like to code on an old machine like this, you’ll enjoy the video. Even so, the process isn’t quite authentic since he uses a more modern editor written for the Centurion. Most editors from those days were more like CP/M ed or DOS edlin, which were painful, indeed.

The target program is a hard drive test, so part of it isn’t just knowing assembly but understanding how to interface with the machine. That was pretty common, too. You didn’t have a lot of help from canned routines in those days. For example, it was common to read an entire block from a hard drive, tape, or drum and have to figure out what part of it you were actually interested in instead of, say, opening a file and reading a stream of characters.

If nothing else, fast forward over to the 25-minute mark and see what a hard drive from that era looked like. Guess how much storage was on that monster? If you guessed more than 10 MB, you probably didn’t live through the 1980s. We won’t even guess what the price tag was, but you can bet it was spendy.

If you think entering programs like this is painful, try a front panel. That made paper tape seem like a great thing.

Continue reading “Assembly Language 80’s Minicomputer Style” →