PDP11s

PDP-11s refer to a family of 16-bit minicomputers designed and produced by Digital Equipment Corporation (DEC) beginning in 1970. The line became one of the most successful and influential in the history of computing, seen in universities, research labs, and industry worldwide. The PDP-11s helped democratize multiuser and multitasking computing and played a key role in the early adoption of the UNIX operating system.

The architecture centers on a 16-bit word, a set of general-purpose registers (R0–R7), and an orthogonal instruction set with multiple addressing modes. This combination gave programmers a flexible and compact instruction repertoire. DEC introduced modular I/O using the Unibus, later complemented by the Q-bus on higher-end models to improve expandability and throughput. The family includes a range of configurations, from smaller, affordable systems to higher-performance models.

Notable models span the mid-range and high-end of the line. Some early and widely deployed machines included the PDP-11/20 and PDP-11/40, with later and more capable variants such as those offering memory management units to support virtual memory for multitasking operating systems. The PDP-11 supported a variety of operating systems beyond UNIX, including RSX-11 and RT-11, contributing to its longevity in both academic and industrial contexts.

Legacy and influence are major aspects of the PDP-11 story. The architecture influenced later DEC designs and the broader industry, reinforcing the popularity of UNIX in the 1970s. The PDP-11 lineage gradually declined as DEC shifted focus to the VAX series, though PDP-11 systems remained in service in some roles for many years and continue to be studied for their historical significance.

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