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


Main article: 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teleprinters such as the Teletype Model 33 ASR or the Friden Flexowriter; from about 1970 these were progressively superseded by CRT–based units such as the DEC VT05, Datapoint 2200 and Lear Siegler ADM-3A.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. 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 mainframes:
CP-40/CMS CP[-67]/CMS ⇶    VM/370 ⇶ VM/SE versions ⇶ VM/SP versions ⇶ VM/XA versions ⇶ VM/ESAz/VM
Transactional systems: CICS, TPFz/TPF

IBM mainframes with non-IBM operating systems:
  Michigan Terminal System (MTS)

  Dartmouth Time Sharing System (DTSS)
  MULTICSUNIX familyLinux

DEC systems:
  BBN Time-Sharing System
  TOPS-10TENEX  ⇉  TOPS-20
  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 TPFz/TPF
APL ("A Programming Language," also "Iverson's Language") System/360, others later[3] 1964–present Kenneth Iverson Mathematically-oriented language and interactive environment, noted for incredible terseness and powerful set processing operators
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/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
CTSS ("Compatible Time Sharing System") modified IBM 7094 1961-1973 MIT Computation Center First-generation "grandfather" of time-sharing systems FMS
→ [numerous other systems]
DTSS ("Dartmouth Time Sharing System") GE 200, GE 635, Honeywell 6000 series 1963-1999 Dartmouth College Early time-sharing system running Dartmouth BASIC and other tools; became the first commercial time-sharing system through General Electric Information Services Division FMS
→ [numerous other systems]
ITS ("Incompatible Timesharing System") PDP-6, PDP-10 1967-1990 MIT Artificial Intelligence Laboratory "Subversive" operating system developed to counter direction of CTSS. The original platform for Macsyma, EMACS and other important applications. CTSS
→ [numerous later systems]
JOSS ("JOHNNIAC Open Shop System") JOHNNIAC, PDP-6 1963-1971? RAND Corporation Lightweight, interactive computing language for non-specialists; did not distinguish operating system from language Highly regarded, but no obvious successors
Linux ubiquitous 1991–present Linus Torvalds, GNU project, open source Operating system dominating current open source activities UNIX
→ [numerous other systems]
Microsoft Windows
(Windows NT 4.0 Terminal Server Edition)
x86, IA-64, others 1985–present Microsoft Ubiquitous GUI operating system MS-DOS
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
Multics GE 645, Honeywell 6180 1969-2000 Project MAC Rich, important system CTSS
⇉ [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
⇶ z/OS-TSO
NOS CDC 60-bit platforms 1976-?? Control Data Corporation System used on most CDC machines[4] MACE→⇶ Kronos
NOS/BE CDC 60-bit platforms 1976-?? Control Data Corporation System used on most CDC machines[4] COSSCOPE →⇶
ORVYL IBM 9672 1967-?? Stanford University Early time-sharing system; source of the WYLBUR editor later used on System/370 platforms
OS/2 (as Citrix Multiuser) x86 1987–present IBM/Microsoft Joint OS effort, now moribund. Still available as eComStation and ArcaOS. DOS ⇶ Microsoft Windows ⇉ OS/2
⇶ eComStation
⇶ ArcaOS 5.0
ROSCOE System/360 and successors 1969-present Applied Data Research (ADR) Early time-sharing editor environment, often used as an alternative to TSO[5] ⇶ WRAP
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
Smalltalk[citation needed] 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
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 ⇶
TOPS-20 DECsystem 20 1976-?? DEC Successor to TOPS-10 but more like TENEX TENEX
TPF S/3x0 1979–present (TPF)
IBM High-performance mainframe transaction platform, successor to ACP, still available as z/TPF ACP
TSOS RCA Spectra 70 and successors 1968-today RCA Early general purpose mainframe OS
TSS-8 PDP-8 1967–?? DEC Simple minicomputer OS RSTS/E
IBM System/360-67 and successors 1967-1971? IBM IBM's original "official" time-sharing system; not a success CTSS
⇶ TSS/370
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
System/370 and successors 1972-1988
2000–present (z/VM)
IBM Proprietary reimplementation of CP/CMS, still available as z/VM CP-40CP-67
OpenVMS VAX, IA-64, DEC Alpha, x86-64 1977–present DEC Popular DEC operating system TENEX
MICAWindows NT
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


  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. ^ McDonnell, Eugene. "The Socio-Technical Beginnings of APL". Retrieved 18 January 2019.
  4. ^ a b "A partial history of CDC Operating Systems", March 1976
  5. ^ Oral History of Martin A. Goetz Archived 2012-03-24 at the Wayback Machine, 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