Real-time bit pattern of PDP-10 physical memory pages allocation and page faults (PCLS).
Free Page
Kernel (SYS)
User Job
PCLS Fault
WHAT IS ITS?
ITS (Incomplete / Incompatible Timesharing System) was developed at the MIT Artificial Intelligence Laboratory starting in 1967 for DEC PDP-6 and PDP-10 computers.
Dissatisfied with earlier systems like CTSS and Multics, MIT AI Lab hackers (including Richard Greenblatt, Tom Knight, and Richard Stallman) built ITS to maximize user freedom, real-time response, and open collaboration.
System Highlights:
- No Passwords: Open multi-user access across the laboratory.
- PCLS (Page Fault Clean-up Interrupts): Execution pauses mid-instruction to resolve system requests cleanly.
- Hackish Tools: Birthplace of EMACS, MACLISP, Scheme, TECO, Zork, and early ARPANET chat.