Compatible Time-sharing System
CTSS, the Compatible Time-sharing System, was probably the first time-sharing system. Developed in the early 1960s at MIT, it ran on a IBM 7094, supporting up to 30 users on a system with just 64kwords of memory and a clock speed well under 1MHz.
CTSS project director Fernando J. Corbató (shown here wearing a bow tie) demonstrates CTSS in 1963 to a reporter from WGBH. Source: Youtube.
Some of the key innovations it brought were
- Users could develop and run programs interactively using teletypwriters.
- Access was protected by logging in with a user name and password, and each running task could not interfere with others.
- It used a disk drive for storage, with users' work partitioned into directories and divided into files.
- It enabled the development of ELIZA, the world's first chatbot, along with document preparation tools and a form of email.
Although it only ever ran on two computers at MIT, it was very influential: many of the CTSS engineers went on to develop Multics, and ideas from CTSS contributed to other OS. Using it today, it seems very familiar to those used to the Unix command line.
Preservation status
There is a good amount of documentation at bitsavers.org covering the machine and the operating system. Probably the best reference is the Programmer's Guide.
The original source code for CTSS was found on a backup tape 20 years ago and has been reconstructed into a version runnable on two emulators
We will use s709 for most of the work on this site as it is slightly easier to use.
Topics
Background
Using the emulators
- A quick tour of CTSS using s709
- Getting data into and out of the system using s709
- If you are interested in using simh instead of s709, see my quickstart repo.
Using CTSS
Future topics
- ELIZA: anatomy of a CTSS application
- QED: a more advanced editor
., the first shell- Document production with TYPSET and RUNOFF
- Email on CTSS
- Preserved transcripts of CTSS usage
- IBM's own time-sharing OS for the 7094