Time-sharing system evolution

This article covers the evolution of time-sharing systems, providing links to major early time-sharing operating systems, showing their subsequent evolution.

Time-sharing

Time-sharing was developed in the late 1950s out of the realization that a single expensive computer could be efficiently utilized if a multitasking, multiprogramming operating system allowed multiple users simultaneous interactive access. Typically an individual user would enter bursts of information followed by long pauses; but with a group of users working at the same time, the pauses of one user would be filled by the activity of the others. Similarly, small slices of time spent waiting for disk, tape, or network input could be granted to other users. Given an optimal group size, the overall process could be very efficient.

Each user would use their own computer terminal; initially electromechanical teleprinters such as the Teletype Model 33 ASR or the Friden Flexowriter, but from about 1970 these were progressively superseded by CRT-based units such as the DEC VT05, Datapoint 2200 and Lear Siegler ADM-3A.

Terminals were initially linked to a nearby computer via current loop or serial cables, by conventional telegraph circuits provided by PTTs and over specialist digital leased lines such T1. Modems such as the Bell 103 and successors, allowed remote and higher-speed use over the analogue voice telephone network.

Family tree of major systems

See details and additional systems in the table below. Relationships shown here are for the purpose of grouping entries and do not reflect all influences (e.g., OS/2 was more influenced by VAX/VMS than by MS-DOS, but its legacy is as an x86 platform). The Cambridge Multiple-Access System^[1][2] was the first time-sharing system developed outside the United States.

Family tree of major time-sharing operating system families
Influences:    → derivation    >> strong influence    > some influence/precedence

CTSS >
	IBM mainframe systems
	CP-40/CMS → CP[-67]/CMS →	VM/370 → VM/XA versions → VM/ESA → z/VM
		VP/CSS
	TSS/360
	OS/MVT-TSO → OS/VS2-TSO → MVS-TSO → z/OS-TSO
	Transactional systems: CICS, TPF → z/TPF
	Non-IBM systems on IBM mainframes
	Michigan Terminal System (MTS)
	MUSIC/SP
	ORVYL
	The MULTICS/UNIX family
	MULTICS > UNIX family >> Linux   MULTICS > PRIMOS > Domain/OS   MULTICS >> Stratus VOS
	DEC time-sharing systems
	TOPS-10 > TENEX >> TOPS-20
	RSTS/E
	RSX-11M >> VAX/VMS → VMS → OpenVMS
	Dartmouth Time Sharing System (DTSS)
	Incompatible Timesharing System (ITS)

System descriptions and relationships

Important time-sharing systems, 1960-1990 (and successors); listed alphabetically

Influences:    → derivation    >> strong influence    > some influence/precedence
System	Platform	Dates in use	Developer	Description	Influences: from→   →to
ACP	S/360 and S/370	1965-1979	IBM	High-performance mainframe transaction platform used in SABRE and PARS	→ TPF → z/TPF
Berkeley Timesharing System	SDS 940	1964-1972	Project Genie	Early general-purpose	>> TENEX
Cambridge Multiple-Access System	Titan, the prototype Atlas 2	1967-1973	University of Cambridge and Ferranti	Multiple Access System	Project MAC→ →UNIX
CANDE	Burroughs large systems	1965?-present	Burroughs	first IDE	(separate evolution)
CICS	S/3x0	1969–present	IBM	Ubiquitous mainframe transaction platform; often used with IBM 3270 terminals and COBOL
CP-40/CMS	customized S/360-40	1967-1972?	IBM's Cambridge Scientific Center	First implementation of full virtualization	CTSS > → CP-67
CP-67/CMS	IBM System/360-67	1967-1975?	IBM's Cambridge Scientific Center	Influential precursor to IBM's VM series, widely distributed as open source	CP-40 → → VP/CSS → VM/370 → z/VM
CTSS ("Compatible Time Sharing System")	modified IBM 7094	1961-1973	MIT Computation Center	First-generation "grandfather" of time-sharing systems	FMS > >> CP-40 >> Multics >> ITS > [numerous other systems]
DTSS ("Dartmouth Time Sharing System")	GE 200	1964-1999	Dartmouth College	Early time-sharing system running Dartmouth BASIC and other tools; the first commercial time-sharing system	FMS > >> CP-40 >> Multics >> ITS > [numerous other systems]
ITS ("Incompatible Timesharing System")	PDP-6, PDP-10	1968?-1990	MIT Artificial Intelligence Laboratory	"Subversive" operating system developed to counter direction of CTSS, the original platform for TECO (parent of EMACS, Macsyma, and other important applications	CTSS > > [numerous later systems]
Linux	ubiquitous	1991–present	Linus Torvalds, GNU project, open source	Operating system dominating current open source activities	UNIX >> minix >> > [numerous other systems]
Microsoft Windows	x86, IA-64, others	1985–present	Microsoft	Ubiquitous GUI operating system	MS-DOS >> OS/2 >> VMS >> Smalltalk >>
MTS (Michigan Terminal System)	IBM S/360-67, S/370	1967-1999	University of Michigan and 7 other universities	First (Nov. 1967) OS to use the virtual memory features of the S/360-67. Early (Sept. 1968) S/360-67 multiprocessor support.	CTSS > DTSS > > UNIX (BSD)
MULTICS	GE 645	1969-2000	Project MAC	Rich, important system	CTSS >> >> UNIX >> [many other systems]
MVS/TSO	System/370 and successors	1971–present	IBM	Probably the most widely used version of TSO, extended version TSO/E, current version zOS-TSO	CTSS > TSS/360 > → z/OS-TSO
NOS	most CDC platforms	1976-??	Control Data Corporation	System used on most CDC machines[3]	Kronos >>
ORVYL	IBM 9672	1967-??	Stanford University	Early time-sharing system; source of the WYLBUR editor later used on System/370 platforms
OS/2	x86	1987–present	IBM/Microsoft	Joint OS effort, now moribund. Still available as eComStation from Serenity Systems International.	VMS >> → Windows NT → eComStation
ROSCOE	System/360 and successors	1969-??	Applied Data Research (ADR)	Early time-sharing editor environment, often used as an alternative to TSO[4]
RSTS/E	PDP-11	1972-1992+	DEC	General-purpose time-sharing for the PDP-11
RSX-11	PDP-11	1972-??	DEC	Real-time operating system for the PDP-11	→ IAS >> VMS
Smalltalk	Xerox Alto, later made portable	1972–present	Xerox PARC, successors	Seminal system for experimental programming, responsible for many modern user interface concepts	>> Apple Lisa >> Apple Macintosh >> Microsoft Windows >> [all GUI platforms]
Stratus VOS	i860, x86, PA-RISC, 68k	1980?-present	Stratus Technologies	High-availability fault-tolerant transaction processing	MULTICS >>
TENEX	PDP-10	1970?-??	Bolt Beranek and Newman	Influential system widely used at research and government sites	>> TOPS-20 >> VMS
TOPS-10	PDP-10	1970-1988? (as TOPS-10) 1964-1970 (as PDP-6 Monitor)	DEC	Widely used at research and academic sites	PDP-6 Monitor → > TENEX >> CP/M
TOPS-20	DECsystem 20	1976-??	DEC	Successor to TOPS-10 but more like TENEX	TENEX > TOPS-10 >
TPF	S/3x0	1979–present (TPF) 2005–present(z/TPF)	IBM	High-performance mainframe transaction platform, successor to ACP, still available as z/TPF	ACP → → z/TPF
TSS-8	PDP-8	1967–??	DEC	Simple minicomputer OS	> RSTS/E
TSS/360 TSS/370	IBM System/360-67 and successors	1967-1971?	IBM	IBM's original "official" time-sharing system; not a success	CTSS > → TSS/370
Unisys/UNIVAC EXEC 8	UNIVAC 1108 and successors	1964-present	Sperry-Rand et al	Many universities and government agencies were early users	EXEC 8 → OS 1100 → OS 2200
UNIX and derivative systems	ubiquitous	1969–present	Bell Laboratories and successors	Ultimately dominated operating system thought, in both proprietary and open-source descendants	Multics >> >> Linux
VM/370	System/370 and successors	1972-1988 2000–present (z/VM)	IBM	Proprietary reimplementation of CP/CMS, still available as z/VM	CP-40 → CP-67 → → VM/ESA → z/VM
VMS and OpenVMS	VAX/VMS, IA-64, DEC Alpha	1977–present	DEC	Popular DEC operating system	TENEX > RSX-11M >> >> Windows NT >> OS/2
VP/CSS	IBM System/360-67, System/370 and successors	1968-1986?	National CSS	Proprietary fork of CP/CMS developed by a time-sharing vendor	CP/CMS →
WYLBUR	System/370 and successors	1967-2009?	Stanford University	Popular editor system originally from ORVYL, used under OS/VS as an alternative to TSO	→ SuperWylbur

See also

• History of CP/CMS has many period details and sources.
• Timeline of operating systems

References

1. Hartley, D. F. (1968), The Cambridge multiple-access system: user's reference manual, Cambridge: Cambridge Univ. Press, ISBN 978-0901224002
2. Wilkes, M.; Needham, R. (1968), "The Design of Multiple-Access Computer Systems: Part 2" (PDF), The Computer Journal, 10 (4): 315–320, doi:10.1093/comjnl/10.4.315
3. "A partial history of CDC Operating Systems", March 1976
4. Oral History of Martin A. Goetz, co-founder of Applied Data Research (ADR), interviewed by: Burt Grad and Luanne Johnson, December 10, 1985 at Princeton, New Jersey, Computer History Museum Reference No. X4579.2008