Definition

PDP-11 (Programmed Data Processor-11)

Part of the Hardware glossary:

PDP-11 (Programmed Data Processor-11) is one of the most famous computers in computing history, one of a series manufactured by Digital Equipment Corporation ( DEC ) from the early 1960s through the mid-1990s. PDP-11, which was sold in 1970 for $10,800, was the only 16-bit computer ever made by the company.

The PDP-11 had a number of other features that distinguished it from most of its contemporaries, including multiple (eight) register s; multiple addressing mode s; a hardware stack ; processor error trap s; and a separate communications path for memory and peripherals (called the UNIBUS ) that could move data independently of the processor. Many early developers and users of the UNIX operating system ran it on the PDP-11 after the original Multics system was no longer available.

Before the 1970s, computers were not thought to be something that the average person would buy or use. At about $1,000,000, they were prohibitively expensive. Furthermore, computers of the time were so large and complex that a computer center was required to house one and a sizable staff was required to look after it. To dissociate their product line from these public perceptions, DEC didn't refer to the PDP as a computer at all, but used its name, the Programmed Data Processor, as a generic term. DEC's first model, PDP-1 sold for $120,000 - about 40 times the price of a good computer today, but a bargain at the time.

DEC was acquired by Compaq Computers in 1998.

This was last updated in March 2011
Contributor(s): Shailender Chennamaneni
Posted by: Margaret Rouse

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