ITS 138

ITS 138 front page

Gerald Sussman has preserved a listing of ITS version 138, most likely from 1967. It was mentioned in Grant Fjermedal's 1986 book "The Tomorrow Makers". In 2023, MIT Museum staff began processing the listing, and volunteers transcribed it to machine readable files; at this point there are 25 pages out of more than 120. The TITLE statement on the first line says "ITS 1.0 3/19/67", but there is reason to believe the date has not been kept current with edits.

The format of the listing is in the output of some cross reference tool. Each line is prefixed with a line number and a symbol reference. The last three pages are a table which lists all symbols and where they are defined.

Supported hardware

• Modified TTY device that handles four more teletypes, as per AI memo 105 "Modifications to PDP-6 Teletype Logic". Interestingly, this was done already in August 1966.
• Four GE Datanet 760 CRT consoles, present already in July/September 1967 per Project MAC Progress Report IV.
• The second generation vidissector, "TVB". Mentioned in AI memo 113. The input is slaved to the Type 340 deflectors.
• 16K core, or (preferably) 256K moby core memory from Fabri-Tek. The latter was installed in 1966, but took almost a year to be fully operational.
• DEC Type 555 "microtapes" with data channel.
• DEC Type 340 display.
• Line printer.

Source code walkthrough

Page	Description
1-3	Basic definitions, accumulators, PI channel assignments, etc.
4	"GO" entry point, initialization. Jumps to the core job.
5-7	Handlers for clock, parity error, and other processor interrupts.
8-9	Job scheduling.
10	PC "losering"
11-16	Job switching and starting.
17-18	Wait for event.
19-23	UUO handling; system calls and user calls.
24-48	Implementation of most system calls.
49	Vidissector I/O.
50-51	Memory allocation.
52	NUL device I/O.
53-57	USR job device I/O.
58-59	Line printer I/O.
60-69	Teletype I/O.
70-82	GE console I/O.
83-115	Microtape I/O.
116	The system core job.
117-118	Various variables and END statement.

System calls

These are the UUO calls defined on page 19. Note how the symbols do not have the . prefix here.

040	IOT		CALL 1,	DISMIS		OPER 1	ITYI
041	OPEN		CALL 2,	TRAND		OPER 2	LISTEN
042	OPER		CALL 3,	TRANAD		OPER 3	SLEEP
043	CALL		CALL 4,	VALRET		OPER 4	SETMSK
044	USET		CALL 5,	UTRAN		OPER 5	GETMSK
045	BREAK		CALL 6,	CORE		OPER 6	LOGIN
			CALL 7,	TRNDL		OPER 7	CLOSE
			CALL 10,	DSTART		OPER 10	UFLUSH
			CALL 11,	FDELE		OPER 11	ATTY
						OPER 12	GBLTTY
						OPER 13	IPUSH
						OPER 14	IPOP
						OPER 15	DFLUSH
						OPER 16	DSTOP
						OPER 17	RDTIME
						OPER 20	RDSW
						OPER 21	LPEN
						OPER 22	UDISMT

See also

• MIT AI lab IO bus interface for GE Datanet 760

External links

• GitHub repository with ITS 138 page photos and transcribed text.
• ITS 1.4 Reference Manual, is close in time to ITS 138.