by Gerald Boerner


“Software comes from heaven when you have good hardware.”
— Kenneth Olsen, Digital Equipment Corp.

“The nicest thing about standards is that there are so many of them to choose from.”
— Kenneth Olsen, Digital Equipment Corp.

“On almost anything someone does in the computer business, you can go back in the literature and prove someone had done it earlier.”
— Kenneth Olsen, Digital Equipment Corp.

“The beginnings of the hacker culture as we know it today can be conveniently dated to 1961, the year MIT acquired the first PDP-1.”
— Eric S. Raymond

“There is no reason anyone would want a computer in their home.”
— Kenneth Olsen, Digital Equipment Corp.

“When I was a teenager in the late 30’s and early 40’s, electronics wasn’t a word. You were interested in radio if you were interested in electronics.”
— Kenneth Olsen, Digital Equipment Corp.

“Home computers were a natural continuum of the ‘personal computers’ that people had at work, in the laboratory, in the military.”
— Kenneth Olsen, in clarification of the previous quote

“A long time ago when the common knowledge was that PCs would run our lives in every detail, I said that if you stole something from the refrigerator at night you didn’t want to enter this into the computer so that it would … mess up the computer plans for coming meals.”
— Kenneth Olsen


The PDP-1 Computer

The PDP-1 (Programmed Data Processor-1) was the first computer in Digital Equipment Corporation’s PDP series and was first produced in 1960. It is famous for being the computer most important in the creation of hacker culture, at MIT, BBN and elsewhere. The PDP-1 was also the original hardware for playing history’s first computerized video game, Steve Russell’s Spacewar!.

pdp-1PDP-1 (above) at the Computer History Museum. At the far right is the IBM Model B typewriter modified by Soroban, with the Type 30 display to its left. The cabinet to the left of the display is the processor itself, the main control panel is visible just above the tabletop, the paper tape reader above it (metallic), and the output of the Teletype model BRPE paper tape punch above that (vertical slot).

The Developer: Kenneth Olsen

Olsen-Kenneth_DECOLSN Kenneth Harry Olsen an American engineer who co-founded Digital Equipment Corporation (DEC) in 1957 with colleague Harlan Anderson and venture capital provided by Georges Doriot’s American Research and Development Corporation. He was born in Stratford, Connecticut. Olsen was a Massachusetts engineer who had been working at MIT Lincoln Laboratory on the TX-2 project.

Ken Olsen was known throughout his career for his paternalistic management style and his fostering of engineering innovation. Ken Olsen’s valuing of innovation and technical excellence spawned and popularized techniques such as engineering matrix management that are broadly employed today throughout many industries.[1]

In 1986, Fortune Magazine named Olsen "America’s most successful entrepreneur." Olsen was the focus of a 1988 biography, "The Ultimate Entrepreneur: The Story of Ken Olsen and Digital Equipment Corporation," by Glenn Rifkin and George Harrar.


PDP-1_control_board_800px It has an 18-bit word and had 4 kilowords as standard main memory (equivalent to 9 kilobytes, or 9,000 bytes), upgradable to 64 kilowords (144 KB). The magnetic core memory’s cycle time was 5 microseconds (corresponding very roughly to a "clock speed" of 200 kilohertz; consequently most arithmetic instructions took 10 microseconds (100,000 operations per second) because they had two memory cycles: one for the instruction, one for the operand data fetch. Signed numbers were represented in one’s complement.

The PDP-1 was built mostly of DEC 1000-series System Building Blocks, using Micro-Alloy and Micro-Alloy-Diffused transistors with a rated switching speed of 5 MHz.


Spacewar_screenshot_800pxThe PDP-1 used punched paper tape as its primary storage medium. Unlike punched card decks, which could be sorted and re-ordered, paper tape was difficult to physically edit. This inspired the creation of text-editing programs such as Expensive Typewriter and TECO. Because it was equipped with online and offline printers that were based on IBM electric typewriter mechanisms, it was capable of what, in eighties terminology, would be called "letter-quality printing" and therefore inspired TJ-2, arguably the first word processor.

PDP-1 and Steve_Russell_Vintage_Computer_Fair_800px_2006 The console typewriter was the product of a company named Soroban Engineering. It was an IBM Model B Electric typewriter mechanism modified by the addition of switches to detect keypresses and solenoids to activate the typebars. It used a traditional typebar mechanism, not the "golfball" IBM Selectric typewriter mechanism, which was not introduced until the next year. Case shifting was performed by raising and lowering the massive type basket. It was equipped with a two-color red-and-black ribbon, and the interface allowed color selection. Programs commonly used color coding to distinguish user input from machine responses. The Soroban mechanism was unreliable and prone to jamming, particularly when shifting case or changing ribbon color, and was widely disliked.

PDP-1_expo_400pxOffline devices were typically Friden Flexowriters that had been specially built to operate with the FIO-DEC character coding used by the PDP-1. Like the console typewriter, these were built around a typing mechanism that was mechanically the same as an IBM Electric typewriter. However, Flexowriters were highly reliable and often used for long unattended printing sessions. Flexowriters had electromechanical paper tape punches and readers which operated synchronously with the typewriter mechanism. Typing was performed about ten characters per second. A typical PDP-1 operating procedure was to output text to punched paper tape using the PDP-1’s "high speed" (60 character per second) Teletype model BRPE punch, then carry the tape to a Flexowriter for offline printing.

Current status

Only three PDP-1 computers are still known to exist, and all three are in the collection of the Computer History Museum. One was a prototype, and the other two are production PDP-1C machines. One of the latter, serial number 55 (the last PDP-1 made) has been restored to working order, is on exhibit, and is demonstrated two Saturdays every month.

The demonstrations include:

  • the game Spacewar!
  • graphics demonstrations such as Snowflake
  • playing music

The restoration is described on a special web page of the Computer History Museum. Simulations of the PDP-1 exist in SIMH and MESS, and paper tapes of the software exist in the archives.

PDP-1 and Steve_Russell_Vintage_Computer_Fair_800px_2006 BBN was DEC’s first customer for the PDP-1. MIT’s PDP-1, donated by DEC in 1961, occupied the room next door to the TX-0 which was on indefinite loan from Lincoln Laboratory.

At the Computer History Museum TX-0 alumni reunion in 1984, Gordon Bell said DEC’s products developed directly from the TX-2, the successor to the TX-0 which had been developed at what Bell thought was a bargain price at the time, about USD $3 million. At the same meeting, Jack Dennis said Ben Gurley’s design for the PDP-1 was influenced by his work on the TX-0 display.

At the museum’s PDP-1 restoration celebration in May 2006, Alan Kotok said his Mac G4 laptop was 10,000 times faster, came with 100,000 times the RAM and 500,000 times the storage, was 1/2000 the size, and cost 1/100 as much.


Background and biographical information is from the Wikipedia articles on:

PDP-1 Computer that can be found at…

Kenneth Olsen that can be found at…