Batch processing The earliest computers were extremely expensive devices, and very slow. Machines were typically dedicated to a particular set of tasks and operated by control panels, the operator manually entering small programs via switches one at a time. These programs might take hours to run. As computers increased in speed,
run times dropped, and soon the time taken to start up the next program became a concern. Newer
batch processing software and methodologies, including batch operating systems such as
IBSYS (1960), decreased these "dead periods" by queuing up programs ready to run. Comparatively inexpensive
card punch or
paper tape writers were used by programmers to write their programs "offline". Programs were submitted to the operations team, which scheduled them to be run. Output (generally printed) was returned to the programmer. The complete process might take days, during which time the programmer might never see the computer. Stanford students made a short film humorously critiquing this situation. 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.
Time-sharing time-sharing at the
University of Wisconsin, 1978 The term time-sharing has had two major uses, one prior to 1960 and the other after. In the earliest uses, the term (used without the hyphen) referred to what we now call
multiprogramming. Robert Dodds claimed to have been first to describe this form of time sharing in a letter he wrote to Bob Bemer in 1949. Later
John Backus described the concept in the 1954 summer session at
MIT. In a 1957 article "How to consider a computer" in
Automatic Control Magazine ,
Bob Bemer outlined the economic reasons for using one large computer shared among multiple users, whose programs are “interleaved.” He also proposed a computer utility that would provide computing power to multiple users, similarly to how electricity is provided by power companies. In June of that year, he gave a paper "Time Sharing in Large Fast Computers" at the first
UNESCO Information Processing Conference in Paris, in which he described solutions to various technical problems raised by the idea of time-sharing. At the same conference, he passed the concept on to
J. C. R. Licklider of
Bolt Beranek and Newman (BBN). This paper was credited by the
MIT Computation Center in 1963 as "the first paper on time-shared computers". After 1960, the meaning of the term
time-sharing shifted from its original usage and it came to mean sharing a computer
interactively among multiple users. --> The first
interactive, general-purpose time-sharing system usable for software development,
Compatible Time-Sharing System, was initiated by
John McCarthy at MIT writing a memo in 1959.
Fernando J. Corbató led the development of the system, a prototype of which had been produced and tested by November 1961.
Philip M. Morse arranged for IBM to provide a series of their mainframe computers starting with the
IBM 704 and then the
IBM 709 product line
IBM 7090 and
IBM 7094. MIT could only use the IBM computers for eight hours a day; another eight hours were available for other colleges and universities; IBM could use their computers for the remaining eight hours, although there were some exceptions. In 1963 a second deployment of CTSS was installed on an IBM 7094 that MIT has purchased using
ARPA money. This was used to support
Multics development at
Project MAC.
Dartmouth Time-Sharing System (DTSS) began service in March 1964.
Development 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. DTSS'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, and unless they received a bill for using the service, rarely thought about how others shared the computer's resources, such as when a large JOSS application caused
paging for all users. The
JOSS Newsletter often asked users to reduce storage usage. Time-sharing was nonetheless an efficient way to share a large computer. DTSS supported more than 100 simultaneous users. Although more than 1,000 of the 19,503 jobs the system completed on "a particularly busy day" required ten seconds or more of computer time, DTSS was able to handle the jobs because 78% of jobs needed one second or less of computer time. About 75% of 3,197 users used their terminal for 30 minutes or less, during which they used less than four seconds of computer time. A football simulation, among
early mainframe games written for DTSS, used less than two seconds of computer time during the 15 minutes of real time for playing the game. With the rise of microcomputing in the early 1980s, time-sharing became less significant, 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 busy.
Time-sharing business Genesis In the 1960s, several companies started providing time-sharing services as
service bureaus. Early systems used
Teletype Model 33 KSR or ASR or Teletype Model 35 KSR or ASR machines in
ASCII environments, and
IBM Selectric typewriter-based terminals (especially the
IBM 2741) 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 storage. Common systems used for time-sharing included the
SDS 940, the
PDP-10, the
IBM 360, and the
GE-600 series. Companies providing this service included
GE's
GEISCO, the
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),
AL/COM,
Bolt, Beranek, and Newman (BBN) and
Time Sharing Ltd. in the
UK. By 1968, there were 32 such service bureaus serving the US
National Institutes of Health (NIH) alone. The
Auerbach Guide to Timesharing (1973) lists 125 different timesharing services using equipment from
Burroughs,
CDC,
DEC,
HP,
Honeywell,
IBM,
RCA,
Univac, and
XDS.
Rise and fall In 1975, acting president of
Prime Computer Ben F. Robelen told stockholders 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, Inc. (OLS), Rapidata and
Time Sharing Ltd. The advent of the
personal computer marked the beginning of the decline of time-sharing. The economics were such that computer time went from being an expensive resource that had to be shared to being so cheap that computers could be left to sit idle for long periods in order to be available as needed.
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.
Time-sharing in the United Kingdom •
Time Sharing Limited (TSL, 1969–1974) - launched using DEC systems.
PERT was one of its popular offerings. TSL was acquired by
ADP in 1974. • OLS Computer Services (UK) Limited (1975–1980) - using HP & DEC systems.
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.
Security 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 could result in a potentially wrong output. With multiple users though, 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 customers. Time-sharing in the form of
shell accounts has been considered a risk. ==Notable time-sharing systems==