Misplaced Pages

#921078

68-522: IBM also distributed other systems in source code form. Most early operating systems were shipped in this way. Source distribution of the VM family of operating systems continued for several decades after it supplanted CP/CMS from the Type-III Library, and TPF was always distributed in source form, apparently continued today with z/TPF . Unlike Type-III software, such systems were supported by IBM. During

136-634: A Token Ring or Ethernet network). The stack provided support for Telnet connections, from either simple line-mode terminal emulators or VT100-compatible emulators, or proper IBM 3270 terminal emulators. The stack also provided an FTP server. IBM also produced an optional NFS server for VM; early versions were rather primitive, but modern versions are much more advanced. There was also a fourth networking option, known as VM/Pass-Through Facility (or more commonly called, PVM). PVM, like VTAM, allowed for connections to remote VM/CMS systems, as well as other IBM systems. If two VM/CMS nodes were linked together over

204-534: A channel-to-channel link or bisync link (possibly using a dialup modem or leased line), a user could remotely connect to either system by entering "DIAL PVM" on the VM login screen, then entering the system node name (or choosing it from a list of available nodes). Alternatively, a user running CMS could use the PASSTHRU program that was installed alongside PVM, allowing for quick access to remote systems without having to log out of

272-436: A configuration would be unusual). It now runs only as a guest OS under VM. This is because CMS relies on a hypervisor interface to VM-CP, to perform file system operations and request other VM services. This paravirtualization interface: CMS and other operating systems often have DASD requirements much smaller than the sizes of actual volumes. For this reason CP allows an installation to define virtual disks of any size up to

340-488: A dialog to create an email, from which the user could send it. If the user specified an address in the form of user at node , the email file would be delivered to RSCS, which would then deliver it to the target user on the target system. If the site has TCP/IP installed, RSCS could work with the SMTP service machine to deliver notes (emails) to remote systems, as well as receive them. If the user specified user at some.host.name ,

408-497: 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 . IBM loaned those mainframes at no cost to MIT along with the staff to operate them and also provided hardware modifications mostly in

476-737: A patent application in the United Kingdom for "time-sharing" in February 1959. He gave a paper "Time Sharing in Large Fast Computers" at the first UNESCO Information Processing Conference in Paris in June that year, where he passed the concept on to J. C. R. Licklider . This paper was credited by the MIT Computation Center in 1963 as "the first paper on time-shared computers". The meaning of

544-538: A public demonstration at Robert Allerton Park near the University of Illinois in early 1961. Bitzer has long said that the PLATO project would have gotten the patent on time-sharing if only the University of Illinois had not lost the patent for two years. The first interactive , general-purpose time-sharing system usable for software development, Compatible Time-Sharing System , was initiated by John McCarthy at MIT writing

612-532: A read password, a write password, and a multi-write password). SFS directories also solve the issues that may arise when two users write to the same CMS minidisk at the same time, which may cause disk corruption (as the CMS VM performing the writes may be unaware that another CMS instance is also writing to the minidisk). The file pool server machines also serve a closely related filesystem: the Byte File System. BFS

680-599: 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 . JOSS began time-sharing service in January 1964. Dartmouth Time-Sharing System (DTSS) began service in March 1964. 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

748-457: A shell can then be started with OPENVM SHELL . Unlike the normal SFS, access to BFS filesystems is controlled by POSIX permissions (with chmod and chown ). Starting with z/VM Version 3, IBM integrated OpenEdition into z/VM and renamed it OpenExtensions. OpenEdition and OpenExtensions provide POSIX.2 compliance to CMS. Programs compiled to run under the OpenExtensions shell are stored in

SECTION 10

#1733084803922

816-516: A single system. z/VM was first released in October 2000 and remains in active use and development. IBM and third parties have offered many applications and tools that run under VM. Examples include RAMIS , FOCUS , SPSS , NOMAD , DB2 , REXX , RACF , and OfficeVision . Current VM offerings run the gamut of mainframe applications, including HTTP servers, database managers, analysis tools, engineering packages, and financial systems. As of release 6,

884-471: A single user (or virtual machine) could not use more than 16 MB. The functions of the spool filesystem were also improved, allowing 9900 spool files to be created per user, rather than 9900 for the whole system. The architecture of the spool filesystem was also enhanced, each spool file now had a unique user ID associated with it, and reader file control blocks were now held in virtual storage. The system could also be configured to deny certain users access to

952-416: A user account is configured to only use SFS (and does not own any minidisks), the user's A-disk will be FILEPOOL:USERID. and any subsequent directories that the user creates will be FILEPOOL:USERID.DIR1.DIR2.DIR3 where the equivalent UNIX file path is /dir1/dir2/dir3 . SFS directories can have much more granular access controls when compared to minidisks (which, as mentioned above, can often only have

1020-745: A very substantial portion of the mid-range machines that were built in Endicott. Before fifteen years had passed, there would be more VM licenses than MVS licenses. A PC DOS version that runs CMS on the XT/370 (and later on the AT/370) is called VM/PC. VM/PC 1.1 was based on VM/SP release 3. When IBM introduced the P/370 and P/390 processor cards, a PC could now run full VM systems, including VM/370, VM/SP, VM/XA, and VM/ESA (these cards were fully compatible with S/370 and S/390 mainframes, and could run any S/370 operating system from

1088-478: A virtual machine and CP." The instruction contains two four-bit register numbers, called Rx and Ry, which can "contain operand storage addresses or return codes passed to the DIAGNOSE interface," and a two-byte code "that CP uses to determine what DIAGNOSE function to perform." The available diagnose functions include: At one time, CMS was capable of running on a bare machine , as a true operating system (though such

1156-424: Is capable of running any software that could be run on a stand-alone machine. A given VM mainframe typically runs hundreds or thousands of virtual machine instances. VM-CP began life as CP-370, a reimplementation of CP-67 , itself a reimplementation of CP-40 . Running within each virtual machine is another operating system, a guest operating system . This might be: The following versions are known: The CMS in

1224-552: Is provided by either C/370 or C for VM/ESA. Neither the CMS filesystem nor the standard VM Shared File System has any support for UNIX-style files and paths; instead, the Byte File System is used. Once a BFS extent is created in an SFS file pool, the user can mount it using the OPENVM MOUNT /../VMBFS:fileservername:filepoolname /path/to/mount/point . The user must also mount the root filesystem, done with OPENVM MOUNT /../VMBFS:VMSYS:ROOT/ / ,

1292-468: Is referred to as a CMS minidisk, although CMS is not the only system that can use them. It is common practice to define full volume minidisks for use by such guest operating systems as z/OS instead of using DEDICATE to assign the volume to a specific virtual machine. In addition, "full-pack links" are often defined for every DASD on the system, and are owned by the MAINT userid. These are used for backing up

1360-715: 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. Although many time-sharing services simply closed, Rapidata held on, and became part of National Data Corporation . It

1428-683: Is used to store files on a UNIX-style filesystem. Its primary use is for the VM OpenExtensions POSIX environment for CMS. The CMS user virtual machines themselves communicate with the SFS server virtual machines through the IUCV mechanism. The early history of VM is described in the articles CP/CMS and History of CP/CMS . VM/370 is a reimplementation of CP/CMS, and was made available in 1972 as part of IBM's System/370 Advanced Function announcement (which added virtual memory hardware and operating systems to

SECTION 20

#1733084803922

1496-516: 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

1564-458: The System/370 series). Early releases of VM through VM/370 Release 6 continued in open source through 1981, and today are considered to be in the public domain . This policy ended in 1977 with the chargeable VM/SE and VM/BSE upgrades and in 1980 with VM/System Product (VM/SP). However, IBM continued providing updates in source form for existing code for many years, although the upgrades to all but

1632-537: 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 . In 1975, acting president of Prime Computer Ben F. Robelen told stockholders that "The biggest end-user market currently

1700-514: The "recovery machine" that does not actually serve any files; VMSERVS, the server for the VMSYS filepool; and VMSERVU, the server for the VMSYSU (user) filepool. The file pool server machines own several minidisks, usually including a CMS A-disk (virtual device address 191, containing the file pool configuration files), a control disk, a log disk, and any number of data disks that actually store user files. If

1768-436: The 1960s, its emergence as the prominent model of computing in the 1970s represented a major technological shift in the history of computing. By allowing many 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

1836-422: The 1970s, Ted Nelson 's original " Xanadu " hypertext repository was envisioned as such a service. 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

1904-465: The 31-bit era, e.g., MVS/ESA, VSE/ESA). In addition to the base VM/SP releases, IBM also introduced VM/SP HPO (High Performance Option). This add-on (which is installed over the base VM/SP release) improved several key system facilities, including allowing the usage of more than 16 MB of storage (RAM) on supported models (such as the IBM 4381). With VM/SP HPO installed, the new limit was 64 MB; however,

1972-629: The IBM Corporation as part of its service to customers, but recipients are expected to make the final evaluation as to the usefulness of the programs in their own environment. There is no committed maintenance for Type III Programs, nor does IBM make any warranty, expressed or implied, as to the documentation, function or performance of such programs. Originally, these programs were not individually priced, but were provided at no cost as part of IBM’s service. In 1969, IBM “unbundled,” separately pricing hardware, software, and services. The Type-III library

2040-571: The MVS Performance Group in the early days of MVS, when its performance was a sore topic). In 1983, the teddy bear became VM's de facto mascot at SHARE 60, when teddy bear stickers were attached to the nametags of "cuddlier oldtimers" to flag them for newcomers as "friendly if approached". The bears were a hit and soon appeared widely. Bears were awarded to inductees of the "Order of the Knights of VM", individuals who made "useful contributions" to

2108-516: The NOTE program would deliver the email to the SMTP service machine, which would then route it out to the destination site on the Internet. VM's role changed within IBM when hardware evolution led to significant changes in processor architecture. Backward compatibility remained a cornerstone of the IBM mainframe family, which still uses the basic instruction set introduced with the original System/360 ; but

IBM Type-III Library - Misplaced Pages Continue

2176-798: The Program Information Department (PID) for distribution. These programs and their documents were distributed in the author's original form and were not subjected to any formal testing. These libraries were maintained by the IBM Program Information Department, headquartered in Hawthorne, New York , with its distribution center in Mechanicsburg, Pennsylvania , which published separate catalogs for each compatible family of IBM Processors. [The software] has not been submitted to any formal test. Type III Programs are provided by

2244-399: The SFS does. SFS also introduces more granular security. With CMS minidisks, the system can be configured to allow or deny users read-only or read-write access to a disk, but single files cannot have the same security. SFS alleviates this, and vastly improves performance. The SFS is provided by service virtual machines. On a modern VM system, there are usually three that are required: VMSERVR,

2312-521: The VM/370 Control Program has a number of commands for General Users, concerned with defining and controlling the user's virtual machine. Lower-case portions of the command are optional Starting with VM/ESA Version 2, IBM introduced the chargeable optional feature OpenEdition for VM/ESA Shell and Utilities Feature , which provides POSIX compatibility for CMS. The stand-out feature was a UNIX shell for CMS. The C compiler for this UNIX environment

2380-451: The business of selling computer systems. Melinda Varian provides this fascinating quote, illustrating VM's unexpected success: The marketing forecasts for VM/370 predicted that no more than one 168 would ever run VM during the entire life of the product. In fact, the first 168 delivered to a customer ran only CP and CMS. Ten years later, ten percent of the large processors being shipped from Poughkeepsie would be destined to run VM, as would

2448-401: The capacity of the device. For CKD volumes, a minidisk must be defined in full cylinders. A minidisk has the same attributes as the underlying real disk, except that it is usually smaller and the beginning of each minidisk is mapped to cylinder or block 0. The minidisk may be accessed using the same channel programs as the real disk. A minidisk that has been initialized with a CMS file system

2516-416: The community-support model of early CP/CMS users. In the meantime, the system struggled with political infighting within IBM over what resources should be available to the project, as compared with other IBM efforts. A basic problem with the system was seen at IBM's field sales level: VM/CMS demonstrably reduced the amount of hardware needed to support a given number of time-sharing users. IBM was, after all, in

2584-410: The community. Time-sharing In computing , time-sharing is the concurrent sharing of a computing resource among many tasks or users by giving each task or user a small slice of processing time . This quick switch between tasks or users gives the illusion of simultaneous execution. It enables multi-tasking by a single user or enables multiple-user sessions. Developed during

2652-440: 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. As of 1972 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

2720-453: The development of new interactive applications . 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 to run. As computers grew in speed, run times dropped, and soon

2788-438: 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

IBM Type-III Library - Misplaced Pages Continue

2856-444: The form of RPQs as prior customers had already commissioned the modifications. There were certain stipulations that governed MIT's use of the loaned IBM hardware. MIT could not charge for use of CTSS. 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

2924-517: The free base required a license. As with CP-67, privileged instructions in a virtual machine cause a program interrupt, and CP simulated the behavior of the privileged instruction. VM remained an important platform within IBM, used for operating system development and time-sharing use; but for customers it remained IBM's "other operating system". The OS and DOS families remained IBM's strategic products, and customers were not encouraged to run VM. Those that did formed close working relationships, continuing

2992-505: The limit entirely, and some modern z/VM systems can have as many as 80 processors. The per-VM limit for defined processors is 64. When IBM introduced the System/370 Extended Architecture on the 3081 , customers were faced with the need to run a production MVS/370 system while testing MVS/XA on the same machine. IBM's solution was VM/XA Migration Aid, which used the new Start Interpretive Execution (SIE) instruction to run

3060-570: The mainframe era, IBM made a wide variety of programs available to its customers. Programs were offered in two broad categories. The first category of programs were IBM developed and supported. These were termed Type I (Programming systems) and Type II (Application Programs). These programs were subjected to formal testing and were maintained by IBM. The second category of available programs were termed Type III and Type IV programs. Type III (IBM Contributed Programs) and Type IV (Customer Contributed Programs) were programs of general interest contributed to

3128-571: The many Type-III programs offered by IBM include: VM (operating system) VM (often: VM/CMS ) is a family of IBM virtual machine operating systems used on IBM mainframes System/370 , System/390 , zSeries , System z and compatible systems, including the Hercules emulator for personal computers. The heart of the VM architecture is the Control Program or hypervisor abbreviated CP, VM-CP and sometimes, ambiguously, VM. It runs on

3196-472: The most part. The concept is claimed to have been first described by Robert Dodds in a letter he wrote in 1949 although he did not use the term time-sharing . Later John Backus also described the concept, but did not use the term, in the 1954 summer session at MIT . Bob Bemer used the term time-sharing in his 1957 article "How to consider a computer" in Automatic Control Magazine and it

3264-655: The name refers to the Conversational Monitor System, a component of the product that is a single-user operating system that runs in a virtual machine and provides conversational time-sharing in VM. IBM coined the term hypervisor for the 360/65 and later used it for the DIAG handler of CP-67. The Diagnose instruction ('83'x—no mnemonic) is a privileged instruction originally intended by IBM to perform "built-in diagnostic functions, or other model-dependent functions." IBM repurposed DIAG for "communication between

3332-455: The need for efficient use of the 64-bit zSeries made the VM approach much more attractive. VM was also utilized in data centers converting from DOS/VSE to MVS and is useful when running mainframe AIX and Linux , platforms that were to become increasingly important. The current z/VM platform has finally achieved the recognition within IBM that VM users long felt it deserved. Some z/VM sites run thousands of simultaneous virtual machine users on

3400-466: The physical hardware, and creates the virtual machine environment. VM-CP provides full virtualization of the physical machine – including all I/O and other privileged operations. It performs the system's resource-sharing, including device management, dispatching, virtual storage management, and other traditional operating system tasks. Each VM user is provided with a separate virtual machine having its own address space , virtual devices, etc., and which

3468-478: 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

SECTION 50

#1733084803922

3536-648: 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. 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

3604-462: The same format as standard CMS executable modules. Visual editors, such as vi are unavailable, as 3270 terminals are not capable. Users can use ed or XEDIT instead of vi. In the early 1980s, the VM group within SHARE (the IBM user group) sought a mascot or logo for the community to adopt. This was in part a response to IBM's MVS users selecting the turkey as a mascot (chosen, according to legend, by

3672-669: The system using the DASD Dump/Restore program, where the entire contents of a DASD are written to tape (or another DASD) exactly. With modern VM versions, most of the system can be installed to SFS, with the few remaining minidisks being the ones absolutely necessary for the system to start up, and the ones being owned by the filepool server machines. VM/SP Release 6 introduced the Shared File System which vastly improved CMS file storage capabilities. The CMS minidisk file system does not support directories (folders) at all, however,

3740-671: The term time-sharing has shifted from its original usage. From 1949 to 1960, time-sharing was used to refer to multiprogramming without multiple user sessions. Later, it came to mean sharing a computer interactively among multiple users. In 1984 Christopher Strachey wrote he considered the change in the meaning of the term time-sharing a source of confusion and not what he meant when he wrote his paper in 1959. There are also examples of systems which provide multiple user consoles but only for specific applications, they are not general-purpose systems. These include SAGE (1958), SABRE (1960) and PLATO II (1961), created by Donald Bitzer at

3808-724: 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

3876-469: 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

3944-473: 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)

4012-646: The user's session. PVM also supported accessing non-VM systems, by utilizing a 3x74 emulation technique. Later releases of PVM also featured a component that could accept connections from a SNA network. VM was also the cornerstone operating system of BITNET , as the RSCS system available for VM provided a simple network that was easy to implement, and somewhat reliable. VM sites were interlinked by means of an RSCS VM on each VM system communicating with one another, and users could send and receive messages, files, and batch jobs through RSCS. The "NOTE" command used XEDIT to display

4080-541: The vector facility (by means of user directory entries). Releases of VM since VM/SP Release 1 supported multiprocessor systems. System/370 versions of VM (such as VM/SP and VM/SP HPO) supported a maximum of two processors, with the system operating in either UP (uniprocessor) mode, MP (multiprocessor) mode, or AP (attached processor) mode. AP mode is the same as MP mode, except the second processor lacks I/O capability. System/370-XA releases of VM (such as VM/XA) supported more. System/390 releases (such as VM/ESA) almost removed

4148-402: The virtual machine. SIE automatically handled some privileged instructions and returned to CP for cases that it couldn't handle. The Processor Resource/System Manager (PR/SM) of the later 3090 also used SIE. There were several VM/XA products before it was eventually supplanted by VM/ESA and z/VM. In addition to RSCS networking, IBM also provided users with VTAM networking. ACF/VTAM for VM

SECTION 60

#1733084803922

4216-402: 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

4284-405: Was eventually replaced by several different product designations. Programs contributed by customers were known as " Installed User Programs " (IUPs) and those developed by IBM employees as " Field Developed Programs " (FDPs). The "field developed" moniker was something of a misnomer, as quite a few FDPs were written by employees in the IBM programming groups rather than by field personnel. Some of

4352-424: Was fully compatible with ACF/VTAM on MVS and VSE. Like RSCS, VTAM on VM ran under the specialized GCS operating system. However, VM also supported TCP/IP networking. In the late 1980s, IBM produced a TCP/IP stack for VM/SP and VM/XA. The stack supported IPv4 networks, and a variety of network interface systems (such as inter-mainframe channel-to-channel links, or a specialized IBM RT PC that would relay traffic out to

4420-560: Was reported the same year he used the term time-sharing in a presentation. In a paper published in December 1958, W. F. Bauer 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." Christopher Strachey , who became Oxford University's first professor of computation, filed

4488-560: 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

4556-479: 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. Beginning in 1964, the Multics operating system was designed as a computing utility , modeled on the electrical or telephone utilities. In

4624-539: 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

#921078