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Time Sharing Option (TSO) is an interactivetime-sharing environment forIBM mainframe operating systems, includingOS/360 MVT,OS/VS2 (SVS),MVS,OS/390, andz/OS.
In computing,time-sharing is a design technique that allows many people to use a computer system concurrently and independently—without interfering with each other.[1] Each TSO user has his own region of storage, protected from alteration by other users.
TSO is most commonly used by mainframesystem administrators and programmers. It provides:
TSO interacts with users in either a line-by-line mode or in a full screen, menu-driven mode. In the line-by-line mode, the user enters commands by typing them in at the keyboard; in turn, the system interprets the commands, and then displays responses on the terminal screen. But most mainframe interaction is actually viaISPF, which allows for customized menu-driven interaction. This combination is calledTSO/ISPF. TSO can also provide a Unix-style environment on OS/390 and z/OS via theUNIX System Servicescommand shell, with or without ISPF.
TSO commands can be embedded inREXX andooRexx execs orCLISTs, which can run interactively or in batch.
TSO eliminated the need to punch cards on akeypunch machine, and to sendcard decks to the computer room to be read by acard reading machine.
Prior to TSO, IBM had introduced limited function time sharing applications such as Remote Access ComputingSystem (RAX),Conversational Programming System (CPS), Conversational Remote Batch Entry (CRBE) and Conversational Remote Job Entry (CRJE) for S/360. These either ran user programs only in an interpreter or had no ability to run user programs at all, only to edit, retrieve and submit batch jobs.[a]
In addition, universities had written time sharing systems both for the 360/67, e.g.,Michigan Terminal System (MTS), and for systems prior to S/360, e.g.Compatible Time-Sharing System (CTSS).
When it was introduced in 1971,[3] IBM considered time-sharing an "optional feature", as compared to standardbatch processing, and hence offered TSO as an option forOS/360 MVT. Originally, TSO assigned each user to a TSO region during logon, and used swapping to a swap dataset to allow users to share regions; this remained true forSVS. IBM usedTelecommunications Access Method (TCAM) for terminal I/O until Selectable Unit 13 (TSO/VTAM) added VTAM2 as an alternate access method in MVS.
With the introduction of MVS in 1974, IBM made TSO a standard component of their top-end mainframe operating system. MVS did away with TSO regions and TSO swap data sets; each user had a separate address space, and swapping became the responsibility of the underlying supervisor rather than TSO.
TSO/E ("Time Sharing Option/Extensions") is a set of extensions to the original TSO. TSO/E is a base element of z/OS. Before z/OS, TSO Extensions (TSO/E) was an element of OS/390 and was a licensed program for the MVS andMVS/ESA System Products.[4] Since all z/OS installations have both TSO and TSO/E functions installed, it is normal to refer to both TSO and TSO/E as "TSO".
When first released, TSO module names outside ofSVCs always had the "prefix" IKJ, in some cases followed by the second and third letters of an associated pre-TSO functional group (IEA = original functional group of "supervisor", hence a TSO module name of IKJEAxxx, IEB = original functional group of "dataset utilities", hence a TSO module name of IKJEBxxx, etc.).
TSO provides several facilities[5][6]
It is common to run TSO in batch (as opposed to interactively): all the usual TSO line-mode interactive commands can be also executed viaJob Control Language (JCL) by running any of the programsIKJEFT01,IKJEFT1A, andIKJEFT1B and supplying the line commands in a file pointed to by theSYSTSIN DD. The primary difference between the three programs is their handling of return codes from the executed commands.
Batch execution of TSO is one way to allow an IBM mainframe application to accessDB2 resources.
