PDP-10 enthusiasts resurrect ancient MIT operating system

Incompatible Timesharing System now compatible with modern machines

By Richard Chirgwin


Among the more interesting denizens of GitHub are the many projects devoted to rediscovering and preserving the history of computing – such as a system called the Incompatible Timesharing System for the legendary Digital PDP-10.

If Wikipedia is correct, ITS (its name a play on an earlier MIT project, the Compatible Time Sharing System) was created because of dissatisfaction with Multics.

There's at least one ITS characteristic that stands out, to Vulture South's eye: the creation of virtual devices running as user processes, which supported using the then-ARPAnet for distributed computing, with connected machines able to treat each others' storage as if it were local.

The GitHub PDP-10 ITS project says MIT shut down its ITS in 1990, but “enthusiasts continue to operate ITS systems to this day”.

Certainly the original source code is still available, even if's repository hasn't changed in about 15 years.

PDP-10s were big on the ARPAnet in 1977. Image: Computer History Museum under Creative Commons

Vulture South doesn't envy the task that the PDP-10 Group's set itself, even in the limited scope of ITS. They want to find source code for old ITS programs, create an auto-build ITS system, fix and enhance the programs they find, and offer configurable options for hostname, IP address and hardware devices.

And if you have the SIMH emulator (maintained by ex-DEC engineer and VP Robert Supnik, available at the Computer History Simulation Project here) or KLH10, you can experience the joys of running up a ITS.

But wait, there's more: ITS even includes a PDP-11 emulator!

Even to someone too young to be sentimental about the PDP-10, ITS isn't completely useless: it includes TCP support, a Telnet and Supdup (RFC 734) server and clients; as well as FTP and SMTP mail support. ®

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