Retro Computing, Technology

70’s Computer running nuclear plants

On March 28th, 1970 Digital Equipment Corporation announced the PDP-11 one of if not the most successful computers in history. These computers were part of a second wave of computers that were a smaller version of the Mainframe called a minicomputer and are still operating today. A PDP-11 powers a robotic installation at GE Nuclear Plants and will run these systems until 2050. GE is finding it progressively more difficult to find both parts and technical people to support them. They are now resorting to purchasing used parts on eBay. The original PDP-11 expanded to its maximum memory held 248K of memory, a full 26K less than the amount of storage used in the photo of its front panel.

It is hard to imagine what todays computing environment would look like without the PDP-11, it shaped every machine that came after it in some way and had a significant impact on shaping operating systems.

The design of the PDP-11 influenced operating systems like CP/M, MS-DOS and UNIX. The PDP-11 was the smallest computer at the time of its launch that could run UNIX and that made it attractive for use for industrial and scientific projects. It has even been said that parts of the C language took advantage of specific PDP-11 programming features. In 1975 Dave Cutler an engineer at DEC designed 32-bit extensions for the PDP-11. In 1988 Dave left DEC for Microsoft to design Windows NT and even later Windows Azure and XBOX. His systems design background on these older systems were sure to influence future systems.

The PDP-11 was about as far removed from the XBOX as one can imagine. In fact these computers required a lot of cooling as they generated a lot of heat. In the video below you can see a PDP-11 running and outputting information on a teletype.

The first model of the PDP-11 was the PDP-11/20. It lacked even simple hardware support for multiply and divide functions which later models did include but despite its limited capabilities it was a popular option for corporations and governments alike.  It is hard for me today to imagine folks installing UNIX on a PDP-11 in 1970 thinking about how easily you can install Linux a close cousin on the $35 Raspberry Pi.

Because the original PDP-11 was modular, and was built from individual and not highly integrated components, it was cloned and knocked off in many other nation states. It makes sense that other countries also wanted the power that the PDP-11 brought to the table.

Five years after its introduction a model was introduced by LSI that was built on an a design using integrated circuits. The PDP-11 would ship many years and into the 1990’s with the introduction of the PDP-11/93 and PDP-11/94.

The PDP-11 led to VAX which still powers our nations ICBM arsenal and the VAX lead to VMS and OpenVMS operating system, a system still found powering control systems today.

So as I write this today in 2017 I say Happy 47th Birthday to the PDP-11.

Editors Note: Images used in this article By Digital_PDP11-IMG_1498.jpg: Rama & Musée Boloderivative work: Morn – This file was derived from  Digital PDP11-IMG 1498.jpg:, CC BY-SA 2.0 fr,

Leave a Reply