ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/docs/pdp8 From jones@cs.uiowa.edu Sat Dec 10 21:18:00 EST 1994 Organization: Computer Science, University of Iowa, Iowa City, Iowa, USA

In 1957, Ken Olson and Harlan Anderson founded Digital Equipment Corporation (DEC), capitalized at $100,000, and 70% owned by American Research and Development Corporation. The founders wanted to call the company Digital Computer Corporation, but the venture capitalists insisted that they avoid the term Computer and hold off on building computers. With facilities in an old woolen mill in Maynard Massachusetts, DEC's first product was a line of transistorized digital "systems modules", plug-in circuit boards with a few logic gates per board. Starting in 1960, DEC finally began to sell computers (the formal acceptance of the first PDP-1 by BBN is reported in Computers and Automation, April 1961, page 8B). Soon after this, there were enough users that DECUS, the Digital Equipment Computer User's Society was founded.

DEC's first computer, the PDP-1, sold for only $120,000 at a time when other computers sold for over $1,000,000. (A good photo of a PDP-1 is printed in Computers and Automation, Dec. 1961, page 27). DEC quoted prices as low as $85,000 for minimal models. The venture capitalist's insistance on avoiding the term computer was based on the stereotype that computers were big and expensive, needing a computer center and a large staff; by using the term Programmable Data Processor, or PDP, DEC avoided this stereotype. For over a decade, all digital computers sold by DEC were called PDPs. (In early DEC documentation, the plural form "PDPs" is used as a generic term for all DEC computers.)

In the early 1960's, DEC was the only manufacturer of large computers without a leasing plan. IBM, Burroughs, CDC and other computer manufacturers leased most of their machines, and many machines were never offered for outright sale. DEC's cash sales approach led to the growth of third party computer leasing companies such as DELOS, a spinoff of BB&N.

DEC built a number of different computers under the PDP label, with a huge range of price and performance. The largest of these are fully worthy of large computer centers with big support staffs. Some early DEC computers were not really built by DEC. With the PDP-3 and LINC, for example, customers built the machines using DEC parts and facilities. Here is the list of PDP computers:


     =====  ====  ========  ====  =====

     PDP-1  1960  $120,000  18    DEC's first computer

     PDP-2            NA    24    Never built?

     PDP-3            NA    36    One built by a customer, not by DEC.

     PDP-4  1962   $60,000  18    Predecessor of the PDP-7.

     PDP-5  1963   $27,000  12    The ancestor of the PDP-8.

     PDP-6  1964  $300,000  36    A big computer; 23 built, most for MIT.

     PDP-7  1965   $72,000  18    Widely used for real-time control.

     PDP-8  1965   $18,500  12    The smallest and least expensive PDP.

     PDP-9  1966   $35,000  18    An upgrade of the PDP-7.

     PDP-10 1967  $110,000  36    A PDP-6 followup, great for timesharing.

     PDP-11 1970   $10,800  16    DEC's first and only 16 bit computer.

     PDP-12 1969   $27,900  12    A PDP-8 relative.

     PDP-13           NA          Bad luck, there was no such machine.

     PDP-14                       A ROM-based programmable controller.

     PDP-15 1970   $16,500  18    A TTL upgrade of the PDP-9.

     PDP-16 1972      NA    8/16  A register-transfer module system.

Corrections and additions to this list are welcome! The prices given are for minimal systems in the year the machine was first introduced. The bits column indicates the word size. Note that the DEC PDP-10 became the DECSYSTEM-20 as a result of marketing considerations, and DEC's VAX series of machines began as the Virtual Address eXtension of the never-produced PDP-11/78.

It is worth mentioning that it is generally accepted that the Data General Nova (see photo, Computers and Automation, Nov. 1968, page 48) was originally developed as the PDP-X, a 16-bit multi-register version of the PDP-8. A prototype PDP-X was built at DEC before the design was rejected. This and a competing 16-bit design were apparently submitted to Harold McFarland at Carnegie-Mellon University for evaluation; McFarland (and perhaps Gordon Bell, who was at C-MU at the time) evaluated the competing designs and rejected both in favor of what we know as the PDP-11. Some speculate that Bell rejected the Nova design because the competing proposal used the register-transfer notation he had introduced in "Bell and Newell, Computer Structures -- Readings and Examples". An alternate story is that the reason DEC never produced a PDP-13 was because the number 13 had been assigned to what became the Nova; this is unlikely because the PDP-X prototype came before the -11. Neither DEC nor Data General talk much about this, but Ed De Castro, the founding president of Data General, was part of the PDP-8 design team, as were many of the others who came to Data General to build the Nova.

Today, all of the PDP machines are in DEC's corporate past, with the exception of the PDP-11 family, which survives as a line of microcomputers.

Of course, occasionally, some lab builds a machine out of DEC hardware and calls it a PDP with a new number. For example, the Australian Atomic Energy Commission once upgraded a PDP-7 by adding a PDP-15 on the side; they called the result a PDP-22.

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