Time Sharing Option
| Company type | Software feature |
|---|---|
| Industry | Computer software |
| Founded | 1971 |
| Headquarters | United States |
| Products | Interactive time-sharing platform for IBM mainframe operating systems including OS/360 MVT, OS/VS2 (SVS), MVS, OS/390, and z/OS |
Time Sharing Option (TSO) represents an interactive time-sharing platform designed for IBM mainframe operating systems including OS/360 MVT, OS/VS2 (SVS), MVS, OS/390, and z/OS.
Use
Time-sharing technology allows several users to simultaneously and independently utilize a computing system.
Primarily utilized by mainframe system administrators and developers, TSO provides:
- A text editor
- Batch job processing with notification upon completion
- Debugging tools supporting multiple IBM mainframe programming languages
- Compatibility with third-party software, such as querying IMS and DB2 databases
Users can interact with TSO either via its command-line interface or through the menu-driven environment of ISPF, together referred to as TSO/ISPF. On OS/390 and z/OS platforms, TSO additionally offers a Unix-like environment accessible through the UNIX System Services shell.
TSO commands are frequently incorporated into scripting languages like REXX, ooRexx, or CLIST, which may be executed interactively or in batch mode.
By replacing the reliance on physical punched cards, TSO significantly simplified interaction with mainframe systems.
History
Prior to TSO, IBM’s time-sharing capabilities were limited to tools such as Remote Access Computing System (RAX) and Conversational Programming System (CPS) on S/360, which primarily facilitated batch job editing and submission rather than comprehensive user program execution.
Academic institutions developed their own time-sharing systems, including the Michigan Terminal System (MTS) for 360/67 and the earlier Compatible Time-Sharing System (CTSS).
Launched in 1971, IBM introduced time-sharing as an "optional feature" alongside batch processing via TSO for OS/360 MVT. Initially, TSO assigned users to specific regions with swapping managed through swap datasets—a model that persisted under SVS.
With the release of MVS in 1974, TSO was integrated as a standard feature. This version removed regions and swap datasets by allocating each user an independent address space, transferring swapping control to the operating system supervisor.
TSO/E ("Time Sharing Option/Extensions") builds upon the original TSO capabilities. It is an integral component of z/OS and was formerly included in OS/390 as well as licensed for MVS and MVS/ESA. Because every z/OS system contains both TSO and TSO/E, they are commonly referred to collectively as "TSO."
Early TSO modules outside of SVCs typically had names beginning with "IKJ," followed by letters indicating their functional group association (for example, IKJEAxxx from the IEA group responsible for supervisors).
Batch use
TSO is frequently executed in batch mode instead of interactively. All standard line-mode TSO commands can be run through Job Control Language (JCL) by invoking programs IKJEFT01, IKJEFT1A, or IKJEFT1B, with command input provided via a file referenced by SYSTSIN DD. The primary distinction among these programs lies in their handling of return codes from executed commands.
Running TSO in batch mode facilitates efficient access to DB2 resources by IBM mainframe applications.
See also
- Compatible Time-Sharing System (CTSS)
- CP/CMS
- History of IBM mainframe operating systems
- Michigan Terminal System (MTS)
- MUSIC/SP
- ORVYL and WYLBUR
- Time Sharing System (TSS)
Further reading
External links
- A collection of TSO manuals dating back to the early 1970s, accessible through the BitSavers.org repository