Skip to content
[Ken Shirriff] does some of the most interesting teardowns. This time, he’s looking at a French-built minicomputer called the Mitra 125 MS from around 1980. In particular, it was the computer inside Spacelab, a European lab that could fit in the back of the Space Shuttle.
As you might expect, the computer doesn’t contain a microprocessor. Instead, it is a series of cards and, in this post, [Ken’s] looking at the ALU that allows the computer to perform math operations.
The Mitra was a descendant of a 1971 computer, and the “MS” indicated it was a military-grade variant of the computer. Spacelab had three of these. One operated the lab, another handled experiments, and the third was a backup.
At the heart of the board was the 74181 ALU. Well, actually, the 54S181, which was the military-grade high-speed part. Each chip handled four bits of addition, subtraction, or a few other logical operations. No multiply. No divide. Oddly, no right shift, either.
