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D > DIGITAL EQUIPMENT CORPORATION > PDP-8   


Digital Equipment Corporation
PDP-8

The PDP-8 was the first sucessful commercial minicomputer, produced by DEC in the 60s, the first real minicomputer, and the first computer costing less than $20,000.

By late 1973 to 77, the PDP-8 family was the best selling computer in the world. The basic version could sit on a desktop rather than requiring cumbersome racks well known at the time. This compact size caused it to become a popular system in scientific laboratories.

The machine had a now quite strange 12-bit word and four thousand 12-bit words of magnetic core memory. The first model was built without any Integrated circuit - thus no microprocessor - but with discrete transistors mounted on numerous small printed circuit boards called 'flip chips' that were inserted on two backplanes mounted vertically. Both table-top and rack-mount models were available, but adding additional memory required a rack.

CPU was composed of 12 interlinked Register Boards each operating on one bit slice of the 12 bit word and containing an Adder function together with all the major registers - MB, MA, AC, PC. Speed a little less than 1MHz.

The instructions set of the PDP-8 was very limited, only eight basic instructions encoded by the three left bits of each 12-bit word, and one register, the accumulator: However, the PDP-8 could be programmed to do almost anything. It just took longer (sometimes very longer!) to execute programs.

A 110 baud current loop teletype interface allowed an ASR 33 Teletype to be connected, serving as a console as well as a storage device by means of the built-in papertape puncher and reader.

There were numerous variations of the original model over the years, among them:
1966: PDP-8/S - minimum price but slow memory serial logic design
1968: PDP-8/I - first version with integrated circuits
1970: PDP-8/E - New bus structure design called Omnibus
1975: PDP-8/A - Allowed OEMs choice of memory type and quantity

All together, about 50,000 PDP-8 series computers were sold, as well as numerous clones made USA, Asia and East European countries.
In 2000 year, there were still a few PDP8's in operation, mainly in third-world countries.

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The first two of the first three machines I ever worked on were PDP-8''s. A PDP-8A in my high school freshman year in a computer math class and a PDP-8E in my junior and senior years in a computer science/data processing vocational program. They were incredible machines for their time. The one in the vocational program had 2 removable rk05e''s and an rk05f hard drives attached and had 15 terminals attached that could all be used at the same time! It did this with only 32k word memory (appx 48k bytes)! It used an operating system called ''ETOS'' which used the rk05f (5MB fixed version) for virtual memory, one of the rk05e''s for the OS and languages (BASIC, DIBOL, COBOL, and Fortran IV) and the other rk05e for data files.

          
Friday 26th December 2014
Chuck Rose (Vermont, USA)

I am currently leading a group of students in an attempt to restore PDP-8 serial number 85 to operating condition. Our restoration project log is on the web at:
$ http://www.cs.uiowa.edu/~jones/pdp8/UI-8/
We''re posting photos of our work $ currently the focus is on reforming the capacitors in the power supply so we can turn it on. That will take a while, since we had to disassemble quite a bit just to get to some of them.

          
Tuesday 18th February 2014
Douglas W. Jones (Iowa City, Iowa, USA)
Douglas W. Jones

I had the privilege of debugging PDP 8S serial no. 2 in the factory at Maynard in the Traditional products dept. in 1970. It had come to the factory to be rebuilt after being struck by lightning in some place in the Midwest.
It took me almost two months to repair and get it working again. I almost couldn''t believe It was working again after finding so many blown out transistors and other burnt components.

          
Tuesday 12th February 2013
Bob (USA)

 

NAME  PDP-8
MANUFACTURER  Digital Equipment Corporation
TYPE  Professional Computer
ORIGIN  U.S.A.
YEAR  1965
END OF PRODUCTION  1980
BUILT IN LANGUAGE  None
KEYBOARD  ASR-33 Teletype
CPU  CPU was composed of 12 interlinked Register Boards
SPEED  1 MHz (0.5 MIPS)
RAM  4 K of 12 bit words
TEXT MODES  Depending of the terminal used
SIZE / WEIGHT  48 (W) x 55 (D) x 84 (H) cm. / 150 Kgs.
I/O PORTS  110 Baud serial interface
BUILT IN MEDIA  None
POWER SUPPLY  Built-in 780 Watts power supply unit
PERIPHERALS  Memory boards up to 32 Kwords
PRICE  $18.000 (Basic version)


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