[cctalk] Re: Friden (was Silly question about S-100 and video monitors)

He also developed a very interesting calculator, based somewhat on the principles of the LGP-30 computer for Diehl in West Germany. The machine was fully transistorized and used only 142 transistors in its logic. It was based on magnetostrictive delay lines (two of them), and was a fully microcoded architecture, I believe the first electronic calculator to be completely microcoded. Since read-only memory (for the microcode) was either physically very large, or complex and expensive to build at the time (diode ROM, wire rope ROM), the microcode was loaded into the calculator at power-up time from a two channel punched metal tape. One channel provided the clocking, and the other channel provided the bits. It took just under a minute from when the calculator was powered on until the microcode was loaded into a delay line, and from there, all operations of the machine were controlled by the microcode in the delay line. The machine was able to be implemented with so few transistors because the microcode word was quite wide, and was designed so that it was sequentially interpreted as the bits streamed out of the delay line, so not all that many flip flops were needed. Working registers were stored in the other delay line, along with program steps (yes, the machine was programmable). The design was very elegant. The machine debuted as the Diehl Combitron, and the cool thing about its design was that it was really easy to augment by just changing the microcode tape (which was quite easily done...bugfixes could be easly installed even by end-users, though such was discouraged). Soon after the Combitron was introduced, an augmented version was introduced called the Combitron-S that added a small amount of I/O circuitry and additional microcode to implement operations to allow the addition of an external punched paper tape reader/punch.