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The PDP-11 is widely regarded as one of the key computers of the 20th century. Introduced in 1970 and available in a bewildering number of models and configurations, variants were in production until 1990.
Most of the pioneering work on Unix and the C language was done on PDP-11s, so the heritage of the design continues through Linux into the most modern mobile phones. The hardware also pioneered the practical application of many modern concepts, including orthogonal instruction sets, memory-mapped peripherals, and a bewildering array of options and ill-considered cost reductions.
Like almost all of DEC's minicomputers, the design ended its days in a variety of custom processors that used modern techniques to reduce a filing cabinet of silicon to a single chip.
Photo credit: Rupert Goodwins