Tim Mikkelsen's Other Projects
2020-04 DEC PDP-8/E emulator
The PDP-8 was one of the early computers I experienced in college. This project was building a DEC PDP-8 emulator running on a Raspberry Pi.
The PDP-8/e was a model of the PDP-8 line of minicomputers, designed by the Digital Equipment Corporation to be a general purpose computer that inexpensively met the needs of the average user while also being capable of modular expansion to meet the more specific needs of advanced user. The first was built in 1970 and was among the first ever minicomputers and this one was small enough to fit in the back seat of a Volkswagen Beetle Convertible. It originally sold for $6,500 but after 18 months the price dropped to $4995 to make it the only computer under $5000 available at that time.
The basic PDP-8/E system was a 10.5 x 19 x 24 inch rackmount or table top unit that contained the processor, core memory, front panel controls ("programmer's console"), console terminal interface for use with an external data terminal, and power supply.
The PDP-8/e featured a processor with single-address fixed word length, parallel transfer computer using 12-bit, two's complement arithmetic. The 1.2/1.4 microsecond cycle time provides a computation rate of 385,000 additions per second. It was built to be versatile and has a high capacity input/output that supports more than 60 types of peripherals. It could be used for a variety of tasks, from keeping score at Fenway Park to monitoring stimuli to the brain during brain surgery at Massachusetts General Hospital. It was often used for instrumentation and lab control.
The machine had a 12-bit word and 4096 12-bit words of magnetic core memory. The first model was built without any Integrated circuit - thus no microprocessor - but with discrete transistors mounted on numerous small printed circuit boards called 'flip chips' that were inserted on two backplanes mounted vertically. The PDP-8/e featured a processor with single-address fixed word length, parallel transfer computer using 12-bit, two's complement arithmetic. CPU was composed of 12 interlinked Register Boards each operating on one bit slice of the 12 bit word and containing an Adder function together with all the major registers - MB, MA, AC, PC. Speed a little less than 1MHz. The instructions set of the PDP-8 was very limited, only eight basic instructions encoded by the three left bits of each 12-bit word, and one register, the accumulator: However, the PDP-8 could be programmed to do almost anything.
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