Compatible time sharing system

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The Compatible Time-Sharing System ( CTSS ) was one of the first multi-user systems . It was developed at MIT in the early 1960s and was used until 1973.

CTSS was developed and operated on a modified IBM 7094 mainframe computer .

The “Compatible” in the name referred to the possibility of running an unchanged copy of the Fortran Monitor System (FMS) in the background. This made it possible that under this batch processing - the operating system to use programs written on.

There was a problem at the beginning of use, and it was found that larger programs would run forever and never get a result. This happened due to a bug in the code that gave users only one priority, which determined the amount of hardware resources allocated. So if more and more users logged in to run a small program, the large, lengthy programs were deprived of more and more available power, which meant that they could no longer be fully executed. This error was recognized after some time and solved by Tom Hastings, a co-developer of the system, by adding a sub-priority.

CTSS is considered to be the forerunner of Multics , which in turn is the forerunner of Unix .

File system

5/20/63		MAIN	MAD	P	15
5/17/63 	DPFA	SYMTB	P	1
5/17/63 	DPFA	BSS	P	1
5/17/63 	DPFA	FAP	P	2