Brief History of PDP Computers

A brief history of DEC’s PDP computer family traces how machines developed for different markets rather than following one straight line of improvement. The PDP-1 began as an experiment in using general-purpose computers for industrial control, while the cheaper PDP-4 traded speed and compatibility for lower cost. The PDP-5 similarly scaled down the earlier designs for control applications and led to the PDP-8. Chip advances produced the PDP-7 and PDP-9 from the PDP-4 line. In contrast, the PDP-6 was built for time-sharing, with extensive addressable memory and protection that suited large Lisp programs; it evolved into the PDP-10. The later PDP-11 was meant to unite the separate product lines, but it could not match the PDP-10 for some users. The VAX eventually took over the PDP-10’s role. A timeline compares models by inflation-adjusted minimum price and memory-cycle time as a rough measure of speed.

These hardware differences also shaped computing culture. The relatively constrained PDP-7 and PDP-11 fostered Unix, C, and tools designed to do useful work with limited resources, including vi, make, Usenet, awk, and composable shell commands. The PDP-10’s abundant resources supported Emacs and large Lisp systems, alongside projects such as Scheme, TeX, Zork, email, and Microsoft BASIC. The divide was not simply technical: Bell Labs pursued economical computing, while MIT had substantial research funding. Which style a programmer encountered often depended on what their employer could afford, producing contrasting traditions later described as the “New Jersey” and “MIT/Stanford” approaches.