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The PDP-5 was
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...
's first
12-bit Before the widespread adoption of ASCII in the late 1960s, six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This also made it useful for storing a single decimal digit along with a si ...
computer, introduced in 1963.


History

An earlier 12-bit computer, named LINC has been described as the first minicomputer and also "the first modern personal computer." It had 2,048 12-bit words, and the first LINC was built in 1962. DEC's founder, Ken Olsen, had worked with both it and a still earlier computer, the 18-bit 64,000-word TX-0, at MIT's Lincoln Laboratory. Neither of these machines was mass-produced.


Applicability

Although the LINC computer was intended primarily for laboratory use, the PDP-5's 12-bit system had a far wider range of use. An example of DEC's "The success of the PDP-5 ... proved that a market for minicomputers did exist" is: * "Data-processing computers have accomplished for mathematicians what the wheel did for transportation" * "Very reliable data was obtained with ..." * "A PDP-5 computer was used very successfully aboard EvergreenU. S. Coast Guard Oceanographic Vessel — ''Evergreen'' (WAGO-295) for ..." all of which described the same PDP-5 used by the
United States Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...
. The architecture of the PDP-5 was specified by Alan Kotok and Gordon Bell; the principal logic designer was the young engineer Edson de Castro who went on later to found
Data General Data General Corporation was an early minicomputer firm formed in 1968. Three of the four founders were former employees of Digital Equipment Corporation (DEC). Their first product, 1969's Data General Nova, was a 16-bit minicomputer intended to ...
.


Hardware

By contrast with the 4-cabinet PDP-1, the minimum configuration of the PDP-5 was a single 19-inch cabinet with "150 printed circuit board modules holding over 900 transistors." Additional cabinets were required to house many peripheral devices. The minimum configuration weighed about . The machine was offered with from 1,024 to 32,768 12-bit words of core memory. Addressing more than 4,096 words of memory required the addition of a Type 154 Memory Extension Control unit (in modern terms, a
memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit that examines all references to computer memory, memory, and translates the memory addresses being referenced, known as virtual mem ...
); this allowed adding additional Type 155 4,096 word core memory modules.Programmed Data Processor 5
Digital Equipment Corp., Mar. 1964; this is a promotional brochure.


Instruction set

Of the 12 bits in each word, exactly 3 were used for instruction op-codes. The PDP-5's instruction set was later expanded in its successor, the PDP-8. The biggest change was that, in the PDP-5, the program counter was stored in memory location zero, while on PDP-8 computers, it was a register inside the CPU. Another significant change was that microcoded instructions on the PDP-5 could not combine incrementing and clearing the accumulator, while these could be combined on the PDP-8. This allowed loading of many small constants in a single instruction on the PDP-8. The PDP-5 was one of the first computer series with more than 1,000 built.


Software

DEC provided an editor, an assembler, a FORTRAN II Compiler and DDT (a
debugger A debugger is a computer program used to test and debug other programs (the "target" programs). Common features of debuggers include the ability to run or halt the target program using breakpoints, step through code line by line, and display ...
).


Marketplace

With a base price of $27,000 and designed for those not in need of the 18-bit PDP-4, yet having "applications needing solutions too complicated to be solved efficiently by modules systems" the PDP-5, when introduced in 1963, came at a time when the minicomputer market was gaining a foothold.


Photos


PDP-5 computer, including Teletype Model 33 ASR

PDP-5 from Ed Thelen's collection

Front panel of a PDP-5


Notes


References

{{DEC hardware DEC minicomputers 12-bit computers Transistorized computers Computer-related introductions in 1963