# PDP-7

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Minicomputer introduced in 1964

PDP-7 A modified PDP-7 under restoration in Oslo, Norway Manufacturer Digital Equipment Corporation Product family Programmed Data Processor Type Minicomputer Released 1965; 61 years ago (1965) Introductory price US$72,000 (equivalent to $735,586 in 2025) Units sold 120[1][2] Units shipped 120[2] Operating system DECsys, Unix (as "Unics") Memory 4K words (9.2 KB) (expandable up to 64K words (144 KB).)[1] Storage Paper-tape and dual transport DECtape drives (type 555) Display Printer Input Keyboard Platform PDP 18-bit Backward compatibility PDP-1 Predecessor PDP-4 Successor PDP-9

Modified PDP-7 under restoration in Oslo, Norway

PDP-7 at [Living Computer Museum](/source/Living_Computer_Museum)

The **PDP-7** is an [18-bit](/source/18-bit_computing) [minicomputer](/source/Minicomputer) produced by [Digital Equipment Corporation](/source/Digital_Equipment_Corporation) as part of the [PDP](/source/Programmed_Data_Processor) series. Introduced in 1964,[3]: p.8[4] shipped since 1965, it was the first[5] to use their [Flip-Chip](/source/Flip-Chip_module) technology. With a cost of US$72,000, it was cheap but powerful by the standards of the time. The PDP-7 is the third of Digital's 18-bit machines, with essentially the same [instruction set architecture](/source/Instruction_set_architecture) as the [PDP-4](/source/PDP-4) and the [PDP-9](/source/PDP-9).

## Hardware

The PDP-7 was the first [wire-wrapped](/source/Wire_wrap) PDP computer. The computer has a memory cycle time of 1.75 µs and an add time of 4 µs. [Input/output](/source/Input%2Foutput) (I/O) includes a keyboard, printer, [punched tape](/source/Punched_tape) and dual transport [DECtape](/source/DECtape) drives (type 555).[6] The standard [core memory](/source/Magnetic-core_memory) capacity is 4K words (9 KB) but expandable up to 64K words (144 KB).[1]

The PDP-7 weighs about 1,100 pounds (500 kg).[7]

## Software

**DECsys**, the first operating system for DEC's 18-bit computer family (and DEC's first operating system for a computer smaller than its 36-bit timesharing systems), was introduced in 1965. It provides an interactive, single user, program development environment for [Fortran](/source/Fortran) and [assembly language](/source/Assembly_language) programs.[8]

In 1969, [Ken Thompson](/source/Ken_Thompson) wrote the first [UNIX](/source/Unix) system, then named Unics as a pun on [Multics](/source/Multics) despite only using two design elements from Multics,[9][10] in assembly language on a PDP-7,[11] as the operating system for *[Space Travel](/source/Space_Travel_(video_game))*, a game which requires graphics to depict the motion of the planets. A PDP-7 was also the development system used during the development of [MUMPS](/source/MUMPS) at [MGH](/source/Massachusetts_General_Hospital) in [Boston](/source/Boston) a few years earlier.

## Sales

The PDP-7 was described as "highly successful."[12] A combined total of 120 of the PDP-7 and PDP-7A were sold.[3]: p.8 A [DEC](/source/Digital_Equipment_Corporation) publication states that the first units shipped to customers in November 1964.

Eleven systems were shipped to the UK.[5]

## Restorations

At least four PDP-7s were confirmed to still exist as of 2011[5] and a fifth was discovered in 2017.[13]

A PDP-7A (serial number 115) was under restoration in [Oslo](/source/Oslo), Norway;[14] a second PDP-7A (serial number 113) previously located at the [University of Oregon](/source/University_of_Oregon) in its Nuclear Physics laboratory was at the [Living Computer Museum](/source/Living_Computer_Museum) in Seattle, Washington and is completely restored to running condition after being disassembled for transport;[15] Another PDP-7 (serial number 47) is known to be in the collection of Max Burnet near Sydney, Australia, a fourth PDP-7 (serial number 33) is in storage at the [Computer History Museum](/source/Computer_History_Museum) in Mountain View, California and a fifth PDP-7 (serial number 129) belonging to Fred Yerian is also located at the Museum, and has been demonstrated running Unix version 0 and compiling a [B program](/source/B_(programming_language)).[13]

## References

1. ^ [***a***](#cite_ref-liinfopdp7_1-0) [***b***](#cite_ref-liinfopdp7_1-1) [***c***](#cite_ref-liinfopdp7_1-2) ["PDP-7 Definition"](http://www.linfo.org/pdp-7.html). *The Linux Information Project*. September 27, 2007.

1. ^ [***a***](#cite_ref-microsoftpdp7_2-0) [***b***](#cite_ref-microsoftpdp7_2-1) ["1964 — PDP-7"](https://research.microsoft.com/~gbell/Digital/timeline/1964-3.htm). *DIGITAL Computing Timeline* – via Microsoft. Ultimately, 120 PDP-7s were produced and sold.

1. ^ [***a***](#cite_ref-SOEM_DEC57.PRES_3-0) [***b***](#cite_ref-SOEM_DEC57.PRES_3-1) ["Digital Equipment Corporation - 1957 to the present"](https://www.soemtron.org/downloads/decinfo/decdigital1957tothepresent1978-102630349.pdf) (PDF). [Archived](https://ghostarchive.org/archive/20221009/https://www.soemtron.org/downloads/decinfo/decdigital1957tothepresent1978-102630349.pdf) (PDF) from the original on October 9, 2022.

1. **[^](#cite_ref-4)** ["across the editor's desk: COMPUTING AND DATA PROCESSING NEWSLETTER - PDP-7 ANNOUNCED BY DIGITAL"](http://www.bitsavers.org/magazines/Computers_And_Automation/196407.pdf) (PDF). *Computers and Automation*. **XIII** (7): 45. July 1964. [Archived](https://ghostarchive.org/archive/20221009/http://www.bitsavers.org/magazines/Computers_And_Automation/196407.pdf) (PDF) from the original on October 9, 2022. Retrieved September 5, 2020.

1. ^ [***a***](#cite_ref-SOEM_5-0) [***b***](#cite_ref-SOEM_5-1) [***c***](#cite_ref-SOEM_5-2) Tore Sinding Bekkedal (2009). ["Digital Equipment Corporation PDP-7"](https://www.soemtron.org/pdp7.html). *soemtron.org*.

1. **[^](#cite_ref-6)** ["Pdp-7"](https://web.archive.org/web/20130616014501/http://dictionary.reference.com/browse/PDP-7). *reference.com Computing Dictionary*. Archived from [the original](https://dictionary.reference.com/browse/PDP-7) on June 16, 2013.

1. **[^](#cite_ref-7)** ["PDP-7 documents"](http://www.bitsavers.org/pdf/dec/pdp7/). *www.bitsavers.org*. PDP-7_Maint.pdf, p. 1-14 (32).

1. **[^](#cite_ref-DECsys_8-0)** Supnik, Bob (June 19, 2006). ["Technical Notes on DECsys"](http://simh.trailing-edge.com/docs/decsys.pdf) (PDF). [Archived](https://ghostarchive.org/archive/20221009/http://simh.trailing-edge.com/docs/decsys.pdf) (PDF) from the original on October 9, 2022.

1. **[^](#cite_ref-9)** [Ritchie, Dennis M.](/source/Dennis_Ritchie) (1977). [*The Unix Time-sharing System: A retrospective*](https://www.bell-labs.com/usr/dmr/www/retro.pdf) (PDF). Tenth Hawaii International Conference on the System Sciences. [Archived](https://ghostarchive.org/archive/20221009/https://www.bell-labs.com/usr/dmr/www/retro.pdf) (PDF) from the original on October 9, 2022. a good case can be made that UNIX is in essence a modern implementation of MIT's CTSS system

1. **[^](#cite_ref-10)** Seibel, Peter (2009). *Coders at work : reflections on the craft of programming*. New York: Apress. p. 463. [ISBN](/source/ISBN_(identifier)) [9781430219491](https://en.wikipedia.org/wiki/Special:BookSources/9781430219491). The things that I [Ken Thompson] liked [about Multics] enough to actually take were the hierarchical file system and the shell

1. **[^](#cite_ref-11)** Ritchie, Dennis M. ["The Development of the C Language"](https://www.bell-labs.com/usr/dmr/www/chist.html).

1. **[^](#cite_ref-RICM_12-0)** ["DEC PDP-9, System Number 319"](https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-9). *Rhode Island Computer Museum*.

1. ^ [***a***](#cite_ref-Yerian_13-0) [***b***](#cite_ref-Yerian_13-1) ["Restoring UNIX v0 on a PDP-7: A look behind the scenes"](https://livingcomputers.org/Blog/Restoring-UNIX-v0-on-a-PDP-7-A-look-behind-the-sce.aspx). Retrieved November 18, 2019.

1. **[^](#cite_ref-14)** ["Picture album of PDP-7 restoration project"](https://web.archive.org/web/20120715211948/https://heim.ifi.uio.no/~toresbe/dec/pdp7/agi/). Archived from [the original](https://heim.ifi.uio.no/~toresbe/dec) on July 15, 2012. Retrieved June 24, 2005. PDP-7 restoration project located in Oslo, Norway.

1. **[^](#cite_ref-15)** ["Colloquium Details - The University's 40 year old PDP-7 computer is alive again in Seattle"](https://web.archive.org/web/20120314021733/http://www.cs.uoregon.edu/Activities/talks/20110113-Lefevre.php). Archived from [the original](https://www.cs.uoregon.edu/Activities/talks/20110113-Lefevre.php) on March 14, 2012. Retrieved March 2, 2011. University of Oregon's PDP-7 moves to the Living Computer Museum in Seattle, Washington. Alternate host at [https://www.soemtron.org/pdp7no113systeminfo.html](https://www.soemtron.org/pdp7no113systeminfo.html) "January 2011" section.

## External links

- [Information about the PDP-7 and PDP-7/A](https://www.soemtron.org/pdp7.html), including some manuals and a customer list covering 99 of the systems shipped, Digital Equipment Corporation PDP-7.

- [*"The famous PDP-7 comes to the rescue"* (Bell Labs' Unix history)](https://web.archive.org/web/20140402194704/http://www.bell-labs.com/history/unix/pdp7.html) at the [Wayback Machine](/source/Wayback_Machine) (archived April 2, 2014)

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Adapted from the Wikipedia article [PDP-7](https://en.wikipedia.org/wiki/PDP-7) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/PDP-7?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.