DEC PDP-1
In 1960 came the PDP-1 (Programmed Data Processor), the first commercial computer from Digital Equipment Corporation. This machine broke with the computing behemoths of the era through its radically different philosophy of wanting to make the computer accessible and interactive.
Kenneth Olsen and Harlan Anderson, founders of DEC in 1957, designed this computer by drawing inspiration from the MIT Lincoln Laboratory’s TX-2, where they had previously worked. The TX-2 served as their model, but they simplified its architecture while retaining its interactive dimension.
One of the PDP-1’s distinctive features lay in its advanced technical performance. Its ferrite core memory contained 4,096 18-bit words, with a 5-microsecond cycle time. It processed 100,000 additions per second, surpassing contemporary mainframe computers by a factor of 2.5 thanks to its parallel architecture and 5 MHz circuits. The replacement of vacuum tubes with Micro-Alloy and Micro-Alloy-Diffused transistors reduced its footprint to just 17 square meters.
Its originality came above all from the direct interaction it offered with the user. The 16-inch cathode ray display, the Friden Flexowriter keyboard, and the paper tape reader reading 300 lines per second created an immediate user experience, while batch mode largely dominated computing practices.
From a technical standpoint, the PDP-1 brought several lasting innovations. Its instruction set comprised 32 opcodes with arithmetic, logical, and control operations. Its sequence break interrupt system managed multiple peripherals simultaneously. Multiple indirect addressing brought unprecedented flexibility in data processing. These characteristics would mark future generations of computers. This model used one’s complement for its arithmetic, a choice abandoned in later versions in favor of two’s complement, illustrating its experimental nature.
Sold for $120,000, the PDP-1’s commercialization demonstrated DEC’s audacity and challenged IBM computers. This machine required neither air conditioning nor a raised floor, operated on a simple 110-volt power supply, and incorporated self-diagnostic circuits for its maintenance. DEC thus sought to “democratize” access to computing.
The software environment included an assembler with macro support, a text editor called Expensive Typewriter, one of the first Lisp interpreters, and various utilities. The system accepted several additional peripherals such as a punched card reader, a high-speed printer, IBM magnetic tapes, or analog-to-digital converters.
In 1962, MIT students created Spacewar! on this machine. This program, considered the first computer video game, illustrated the PDP-1’s graphical and interactive capabilities while inventing a new form of entertainment.
Despite the production of around fifty units between 1960 and 1969, the PDP-1’s influence established DEC as a major player in interactive computing. Its architecture directly inspired future models in the series: PDP-4, PDP-7, PDP-9, and PDP-15.
Today, the Computer History Museum in Mountain View preserves three PDP-1s, one of which was still operational in 1995. These machines bear witness to a period when computing began to leave calculation centers to move closer to users. Unlike IBM, which favored centralized systems, DEC bet on human-machine interaction and accessibility. The PDP-1’s success validated DEC’s strategy based on less expensive and more accessible machines. The PDP-1 thus marked the first steps toward computing where miniaturization and interactivity were paramount.