Programmed Data Processor-1 | 1959

 

The PDP-1 (Programmed Data Processor-1) was the first computer in the PDP series, produced by Digital Equipment Corporation (DEC) in 1959. This computer is well-known for playing a crucial role in the formation of hacker culture at places like the Massachusetts Institute of Technology (MIT) and Bolt, Beranek and Newman (BBN). The PDP-1 was the original hardware for "Spacewar!", the first-ever mini-computer game developed by Steve Russell.

The PDP-1 uses an 18-bit word size and has a basic memory of 4,096 words, equivalent to approximately 9,216 bytes in 8-bit terms. In practice, the 18-bit words can be processed as three 6-bit characters, allowing for an extension of memory size up to 12,388 bytes. Its core memory has a cycle time of 5.35 microseconds, corresponding to a clock speed of about 187 kilohertz. Most arithmetic instructions take about 10.7 microseconds, allowing the computer to perform approximately 93,458 operations per second. Signed numbers are represented in one's complement format. The computing power of the PDP-1 is roughly comparable to that of a pocket calculator from 1996, with somewhat less memory.

The PDP-1 uses 2,700 transistors and 3,000 diodes, primarily composed of DEC’s 1000 series system building blocks, employing micro-alloy and micro-alloy diffusion transistors with a switching speed of 5 MHz. The system building blocks are packaged in multiple 19-inch racks, which are housed within a large mainframe case. At one end of the mainframe, a hexagonal control panel with switches and lights is positioned at table height, above which are a punch tape reader and writer as standard input/output solutions.

The PDP-1 weighs about 730 kg (1,600 lbs).

The design of the PDP-1 was based on the pioneering TX-0 and TX-2 computers developed at MIT's Lincoln Laboratory. Benjamin Gurley was the chief engineer on this project. After showcasing the prototype at the Eastern Joint Computer Conference in December 1959, DEC delivered the first PDP-1 to BBN in November 1960, and it was officially accepted in early 1961. In September 1961, DEC donated a PDP-1 to MIT, placing it next to the TX-0, which was then on indefinite loan from the Lincoln Laboratory.

In this environment, the PDP-1 quickly replaced the TX-0 as a popular machine among hackers and served as a platform for various computing innovations. This list includes "Spacewar!", one of the earliest digital video games, the first text editor, the first word processor, the first interactive debugger, one of the earliest reliable computer chess programs, the initial time-sharing system (BBN time-sharing system), and early computer-generated music. At a 1984 Computer History Museum reunion of TX-0 alumni, Gordon Bell noted that DEC's product had directly evolved from the TX-2, and that it was developed at a reasonable cost of about $3 million at the time. At the same meeting, Jack Dennis remarked that the PDP-1's design was influenced by the TX-0's display work.

The PDP-1 was sold in its basic form for $120,000 (equivalent to about $1,223,519 in 2023), followed by orders from Lawrence Livermore and the Atomic Energy of Canada Limited (AECL) behind BBN's systems, leading to a total production of 53 PDP-1 units by 1969. These machines remained actively used even into the 1970s, and several were preserved. The MIT unit was donated to the Boston Computer Museum, which later moved to the Computer History Museum (CHM). Inside the PDP-1 case, a later version of "Spacewar!" was still preserved in paper tape form. PDP-1 #44 was discovered in a barn in Wichita, Kansas, in 1988, reportedly belonging to a local aerospace company, and was salvaged for the digital history collection before arriving at the CHM. The AECL computer was sent to Science North but was later decommissioned.

The release of the PDP-1 marked a radical shift in computer design philosophy. It was the first commercial computer focused on user interaction rather than merely efficient use of computing cycles.

The MIT student newspaper, The Tech, referred to the first malicious hacking incident as "phone hacking," in which hackers occupied the phone line with Harvard, configured the PDP-1 to make free calls, resulting in large telephone bills.

The PDP-1 used fanfold punch paper tape as its primary storage medium. Unlike punch card decks, the physical editing of paper tape is cumbersome, which led to the development of text editing programs like Expensive Typewriter and TECO. The PDP-1 was equipped with online and offline printers based on IBM electric typewriter mechanisms, allowing for "letter quality printing" in 1980s terminology, inspiring early word processors like the TJ-2.

The console typewriter was provided by Soroban Engineering, featuring a modified mechanism based on the IBM Model B electric typewriter. It included switches for detecting key inputs and solenoids to activate the typebars. It utilized traditional typebar mechanisms, with the "golf ball" IBM Selectric typewriter mechanism introduced the following year. Upper and lower case letters were selected by lifting or lowering a large typebar basket. Soroban used two-color ink ribbons (red and black) and could select colors via an interface, with programs typically using color coding to distinguish user input from machine responses. However, the Soroban mechanism was less reliable, particularly prone to jams during case switching or ribbon color changes.

For offline devices, a Friden Flexowriter specifically designed to match the PDP-1's FIO-DEC character coding was typically used. Though also based on IBM electric typewriter mechanisms, the Flexowriter was more reliable and frequently used for long-duration unattended printing sessions. The Flexowriter included a punch and reader for paper tape synchronized with the typewriter mechanism, typing at about 10 characters per second. The common operational procedure for the PDP-1 involved using a "high-speed" (60 characters per second) teletypesetter model BRPE punch to output text onto paper tape, which was then manually transported to the Flexowriter for offline printing.

Later, DECtape drives were added to some PDP-1 systems, making it easier to back up programs and data and enabling early time-sharing. This application typically required a secondary storage medium to swap the programs and data in the core memory without manual intervention. In this context, DECtapes offered significantly better reliability, durability, and speed compared to paper tape. Early hard disks were expensive and unreliable, primarily used for swapping speed when operational, rather than for permanent file storage.

The Type 30 precision CRT display was a dot floating display device capable of addressing 1,024 x 1,024 locations at a rate of 20,000 points per second. A special "plot a dot on the CRT" command was used to construct images, which had to be refreshed multiple times per second. The CRT, originally developed for radar purposes, measured 16 inches (41 cm) in diameter and utilized a long persistence P7 phosphor. The Type 30 allowed a light pen to select points on the display, with optional hardware available for character generation and line and curve drawing.