In computing , TIME-SHARING is the sharing of a computing resource
among many users by means of multiprogramming and multi-tasking at the
Its introduction in the 1960s and emergence as the prominent model of
computing in the 1970s represented a major technological shift in the
history of computing.
By allowing a large number of users to interact concurrently with a
single computer, time-sharing dramatically lowered the cost of
providing computing capability, made it possible for individuals and
organizations to use a computer without owning one, and promoted the
interactive use of computers and the development of new interactive
* 1 History
* 1.3 Development
* 1.4.1 Rise and Fall
* 220.127.116.11 Rapidata as an example
* 1.5 The computer utility
* 1.6 Security
* 2 Notable time-sharing systems
* 3 See also
* 4 References
* 5 Further reading
* 6 External links
The earliest computers were extremely expensive devices, and very
slow in comparison to later models. Machines were typically dedicated
to a particular set of tasks and operated by control panels, the
operator manually entering small programs via switches in order to
load and run a series of programs. These programs might take hours, or
even weeks, to run. As computers grew in speed, run times dropped, and
soon the time taken to start up the next program became a concern.
Batch processing methodologies evolved to decrease these "dead
periods" by queuing up programs so that as soon as one program
completed, the next would start.
To support a batch processing operation, a number of comparatively
inexpensive card punch or paper tape writers were used by programmers
to write their programs "offline". When typing (or punching) was
complete, the programs were submitted to the operations team, which
scheduled them to be run. Important programs were started quickly; how
long before less important programs were started was unpredictable.
When the program run was finally completed, the output (generally
printed) was returned to the programmer. The complete process might
take days, during which time the programmer might never see the
The alternative of allowing the user to operate the computer directly
was generally far too expensive to consider. This was because users
might have long periods of entering code while the computer remained
idle. This situation limited interactive development to those
organizations that could afford to waste computing cycles: large
universities for the most part. Programmers at the universities
decried the behaviors that batch processing imposed, to the point that
Stanford students made a short film humorously critiquing it. They
experimented with new ways to interact directly with the computer, a
field today known as human–computer interaction .
Unix time-sharing at the
University of Wisconsin
University of Wisconsin , 1978.
Time-sharing was developed out of the realization that while any
single user would make inefficient use of a computer, a large group of
users together would not. This was due to the pattern of interaction:
Typically an individual user entered bursts of information followed by
long pauses but a group of users working at the same time would mean
that the pauses of one user would be filled by the activity of the
others. Given an optimal group size, the overall process could be very
efficient. Similarly, small slices of time spent waiting for disk,
tape, or network input could be granted to other users.
The concept is claimed to have been first described by
John Backus in
the 1954 summer session at MIT, and later by
Bob Bemer in his 1957
article "How to consider a computer" in Automatic Control Magazine.
In a paper published in December 1958 by W. F. Bauer, he wrote that
"The computers would handle a number of problems concurrently.
Organizations would have input-output equipment installed on their own
premises and would buy time on the computer much the same way that the
average household buys power and water from utility companies."
Implementing a system able to take advantage of this was initially
Batch processing was effectively a methodological
development on top of the earliest systems. Since computers still ran
single programs for single users at any time, the primary change with
batch processing was the time delay between one program and the next.
Developing a system that supported multiple users at the same time was
a completely different concept. The "state" of each user and their
programs would have to be kept in the machine, and then switched
between quickly. This would take up computer cycles, and on the slow
machines of the era this was a concern. However, as computers rapidly
improved in speed, and especially in size of core memory in which
users' states were retained, the overhead of time-sharing continually
decreased, relatively speaking.
The first project to implement a time-sharing system was initiated by
John McCarthy at
MIT in 1959, initially planned on a modified
, and later on an additionally modified
IBM 709 (one of the first
computers powerful enough for time-sharing). One of the deliverables
of the project, known as the
Compatible Time-Sharing System or CTSS,
was demonstrated in November 1961. CTSS has a good claim to be the
first time-sharing system and remained in use until 1973. Another
contender for the first demonstrated time-sharing system was PLATO II,
Donald Bitzer at a public demonstration at Robert Allerton
Park near the University of Illinois in early 1961. But this was a
special purpose system. Bitzer has long said that the PLATO project
would have gotten the patent on time-sharing if only the University of
Illinois had known how to process patent applications faster, but at
the time university patents were so few and far between, they took a
long time to be submitted.
JOSS began time-sharing service in January
The first commercially successful time-sharing system was the
Dartmouth Time Sharing System .
Throughout the late 1960s and the 1970s, computer terminals were
multiplexed onto large institutional mainframe computers (centralized
computing systems), which in many implementations sequentially polled
the terminals to see whether any additional data was available or
action was requested by the computer user. Later technology in
interconnections were interrupt driven, and some of these used
parallel data transfer technologies such as the
IEEE 488 standard.
Generally, computer terminals were utilized on college properties in
much the same places as desktop computers or personal computers are
found today. In the earliest days of personal computers, many were in
fact used as particularly smart terminals for time-sharing systems.
The Dartmouth Time Sharing System's creators wrote in 1968 that "any
response time which averages more than 10 seconds destroys the
illusion of having one's own computer". Conversely, timesharing users
thought that their terminal was the computer. With the rise of
microcomputing in the early 1980s, time-sharing faded into the
background because individual microprocessors were sufficiently
inexpensive that a single person could have all the
CPU time dedicated
solely to their needs, even when idle. However, the Internet brought
the general concept of time-sharing back into popularity. Expensive
corporate server farms costing millions can host thousands of
customers all sharing the same common resources. As with the early
serial terminals, web sites operate primarily in bursts of activity
followed by periods of idle time. This bursting nature permits the
service to be used by many customers at once, usually with no
perceptible communication delays, unless the servers start to get very
In the 1960s, several companies started providing time-sharing
services as service bureaus . Early systems used
Teletype Model 33
Teletype Model 33 KSR
or ASR or Teletype Model 35 KSR or ASR machines in
IBM Selectric typewriter
IBM Selectric typewriter -based terminals (especially the
) with two different seven-bit codes. They would connect to the
central computer by dial-up Bell 103A modem or acoustically coupled
modems operating at 10–15 characters per second. Later terminals and
modems supported 30–120 characters per second. The time-sharing
system would provide a complete operating environment, including a
variety of programming language processors, various software packages,
file storage, bulk printing, and off-line storage. Users were charged
rent for the terminal, a charge for hours of connect time, a charge
for seconds of CPU time, and a charge for kilobyte-months of disk
Common systems used for time-sharing included the
SDS 940 , the
PDP-10 , and the
IBM 360 . Companies providing this service included
GE 's GEISCO,
IBM subsidiary The
Service Bureau Corporation , Tymshare
(founded in 1966),
National CSS (founded in 1967 and bought by Dun &
Bradstreet in 1979), Dial Data (bought by
Tymshare in 1968), and Bolt,
Beranek, and Newman (BBN). By 1968, there were 32 such service bureaus
serving the US
National Institutes of Health
National Institutes of Health (NIH) alone. The
Auerbach Guide to Timesharing (1973) lists 125 different timesharing
services using equipment from Burroughs , CDC , DEC , HP ,
Univac , and XDS .
An example of a UK-based time-sharing bureau business is OLS Computer
Services (UK) Ltd. Previously Leasco Response and later acquired by
On-Line Systems of Pittsburgh, PA, the company operated four HP-2000
TSB (Time shared Basic) systems from its Knightsbridge (later
Islington) headquarters offering off-the-shelf business packages as
well as raw time to universities. In addition to its HP estate a DEC
PDP-10 operated as a front-end processor (FEP) connecting UK users to
16 DEC PDP-11s based in the US. Connectivity was provided via leased
Westrex ASR 33 or Data Dynamics 390 punched-tape enabled teletype
machines connected via Post Office (ex GPO) type 2 modems or acoustic
couplers connecting telephone handsets operating at up to 110cps.
Rise And Fall
In 1975, it was said about one of the major super-mini computer
manufacturers that "The biggest end-user market currently is
time-sharing." For DEC, for a while the second largest computer
company (after IBM), this was also true: Their
PDP-10 and IBM's 360/67
were widely used by commercial timesharing services such as
CompuServe, On-Line Systems (OLS), and Rapidata.
Rapidata As An Example
Although many time-sharing services simply closed, Rapidata held
on, and became part of National Data Corporation. It was still of
sufficient interest in 1982 to be the focus of "A User's Guide to
Statistics Programs: The Rapidata Timesharing System". Even as
revenue fell by 66% and National Data subsequently developed its own
problems, attempts were made to keep this timesharing business going.
THE COMPUTER UTILITY
Beginning in 1964, the
Multics operating system was designed as a
computing utility , modeled on the electrical or telephone utilities.
In the 1970s,
Ted Nelson 's original "Xanadu " hypertext repository
was envisioned as such a service. It seemed as the computer industry
grew that no such consolidation of computing resources would occur as
timesharing systems. In the 1990s the concept was, however, revived in
somewhat modified form under the banner of cloud computing .
Time-sharing was the first time that multiple processes, owned by
different users, were running on a single machine, and these processes
could interfere with one another. For example, one process might
alter shared resources which another process relied on, such as a
variable stored in memory. When only one user was using the system,
this would result in possibly wrong output - but with multiple users,
this might mean that other users got to see information they were not
meant to see.
To prevent this from happening, an operating system needed to enforce
a set of policies that determined which privileges each process had.
For example, the operating system might deny access to a certain
variable by a certain process.
The first international conference on computer security in London in
1971 was primarily driven by the time-sharing industry and its
NOTABLE TIME-SHARING SYSTEMS
Time-sharing system evolution
Significant early timesharing systems:
Allen-Babcock RUSH (Remote Users of Shared Hardware) Time-sharing
IBM S/360 hardware (1966) →
Unix (1971) → UC Berkeley BSD
Time-sharing System → Massachusetts General Hospital
* BBN TENEX → DEC
TOPS-20 , Foonly FOONEX, MAXC OS at PARC ,
Stanford Low Overhead Timesharing System (LOTS)
Berkeley Timesharing System at UC Berkeley
Project Genie →
Scientific Data Systems
SDS 940 (
Tymshare , BBN , SRI , Community
Memory) → BCC 500 → MAXC at PARC
Time-sharing MCP →
HP 3000 MPE
* Cambridge Multiple Access System was developed for the Titan , the
prototype Atlas 2 computer built by
Ferranti for the University of
Cambridge . This was the first time-sharing system developed outside
the United States, and which influenced the later development of UNIX
* Compower Ltd., a wholly owned subsidiary of the National Coal
Board (later British Coal Corporation) in the UK. Originally National
Coal Board (NCB) Computer Services, it became Compower in 1973
providing computing and time-share services to internal NCB users and
as a commercial service to external users. Sold to Philips C
originally based on IBM's
Oregon State University
Oregon State University OS-3, on
CDC 3000 series.
JOSS → JOSS-2 → JOSS-3
RCA TSOS →
Unisys VMOS →
Service in Informatics and Analysis (SIA) , on
CDC 6600 Kronos .
System Development Corporation
Time-sharing System, on the
ORVYL and WYLBUR , on
IBM S/360-67 .
Time-sharing System → SAIL →
* Time Sharing Ltd. (TSL) on DEC
PDP-10 systems → Automatic Data
Processing (ADP), first commercial time-sharing system in Europe and
first dual (fault tolerant) time-sharing system.
* Tone (TSO-like, for VS1 ), a non-
marketed by Tone
Software Co; TSO required VS2.
Tymshare SDS-940 → Tymcom X → Tymcom XX
EXEC 8 → OS 1100 →
* UC Berkeley CAL-TSS, on CDC 6400 .
* XDS UTS → CP-V →
* The Heralds of Resource Sharing , a 1972 film.
* History of
CP/CMS , IBM's virtual machine operating system (CP)
that supported time-sharing (CMS).
IBM M44/44X , an experimental computer system based on an
used to simulate multiple virtual machines.
IBM System/360 Model 67 , the only
IBM S/360 series mainframe to
support virtual memory.
Multiseat configuration , multiple users on a single personal
Project MAC , a
DARPA funded project at
MIT famous for
groundbreaking research in operating systems , artificial intelligence
, and the theory of computation .
TELCOMP , an interactive, conversational programming language
JOSS , developed by BBN in 1964.
Timeline of operating systems
VAX (Virtual Address eXtension), a computer architecture and
family of computers developed by DEC .
* ^ A B DEC TIMESHARING (1965), by Peter Clark, The DEC
Professional, VOLUME 1, Number 1
IBM advertised, early 1960s, with a headline: "This man is
sharing a $2 million computer"
* ^ Eisenson, Arthur; and Yager, Heather (1967). Ellis D.
Kropotchev Silent Film. Stanford University, 1967. This
student-produced film from
Stanford University is a humorous spoof of
the trials and tribulations of a college hacker condemned to use batch
processing. Originally created by Arthur Eisenson and Gary Feldman,
the film gives the viewer a feel for the process of computer
programming in the 1960s. Original music by Heather Yager. Computer
History Museum, Object ID 102695643. Retrieved on 2013-11-29 from
* ^ Backus, John, Computer Advanced Coding Techniques,
page 16-2. The first known description of computer time-sharing.
* ^ Bemer, Bob (March 1957). "Origins of Timesharing".
bobbemer.com. Retrieved June 24, 2016.
* ^ Middleburg, C.A. "Searching Publications on Operating Systems".
arXiv :1003.5525 .
* ^ Bauer, W. F., Computer design from the programmer\'s viewpoint
(Eastern Joint Computer Conference, December 1958) One of the first
descriptions of computer time-sharing.
* ^ "There were no command files supported." - the commands to
compile and then 'link' a program had to be typed in each time. As the
article adds: "No CCL (Concise Command Language)" referring to the DEC
world's equivalent of
* ^ A B McCarthy, John. "REMINISCENCES ON THE HISTORY OF TIME
SHARING". stanford.edu. stanford.edu. Retrieved 12 March 2017.
* ^ J. C. Shaw (1964). "JOSS: a designer's view of an experimental
on-line computing system". Proceeding AFIPS \'64 (Fall, part I)
Proceedings of the October 27-29, 1964, fall joint computer
conference, part I. pp. 455–464.
* ^ dtss.dartmouth.edu/history.php
* ^ Kemeny, John G.; Kurtz, Thomas E. (11 October 1968). "Dartmouth
Time-Sharing". Science. 162: 223–228.
* ^ "TRANSCRIPTS OF 1974 National Computer Conference Pioneer Day
Session". Dartmouth Time Sharing System. Dartmouth College.
IBM 2741 Communication Terminal (PDF). IBM. p. 12.
* ^ "Information Technology Corporate Histories Collection".
Computer History Museum. Retrieved on 2013-11-29 from
Auerbach Publishers, Inc. 1973. Retrieved 2013-11-29.
* ^ Computerworld, June 11, 1975, p. 35
* ^ One Two-page
IBM print ad was headlined "100 or more people can
use IBM's new time-sharing computer at the same time." Originals
were/are? on e-Bay
* ^ p.1425, Encyclopedia of Computer Science, Litton Educational
- "I worked for RapiData Timesharing for about a year circa 1969..."
* ^ someone else: "I worked there for almost 2 years 1977 to 1979."
* ^ NDC started in 1967, and paralleled Rapidata; see Bloomberg's
* ^ Bruce Bosworth, ISBN 978-089529-1-677
* ^ Computerworld, Oct. 6, 1986, p.179, "Rapidata revenue was $11
million ... in 1986, down from ... ($31 million in 1982)."
* ^ Computerworld, Aug.25,1986, p.5, "National Data Corp. said it
is close to reaching an agreement with a buyer of its Rapidata
timesharing division. In May, National Data said it would close down
* ^ National Data Corp became NDC-Health Corp in 2001
* ^ As for a place in history, Rapidata is listed in 'The AUERBACH
Guide to Time Sharing (1973)'
* ^ Silberschatz, Abraham; Galvin, Peter; Gagne, Greg (2010).
Operating system concepts (8th ed.). Hoboken, N.J.: Wiley & Sons. p.
591. ISBN 978-0-470-23399-3 .
* ^ "A Brief Description of Privacy Measures in the RUSH
Time-Sharing System", J.D. Babcock, AFIPS Conference Proceedings,
Spring Joint Computer Conference, Vol. 30, 1967, pp. 301-302.
* ^ Hartley, D. F. (1968), The Cambridge multiple-access system:
user's reference manual, Cambridge: Cambridge Univ. Press, ISBN
* ^ "Time Sharing", James Miller. Retrieve