What is TSO and ISPF?

Time Sharing Option, Interactive System Productivity Facility and REstructured eXtended eXecutor

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Anuj Dhawan
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What is TSO and ISPF?

Postby Anuj Dhawan » Fri May 17, 2013 10:09 am

TSO is Time Sharing Option and ISPF is Interactive System Productivity Facility. TSO and SPF are two separate products, both of which are intended to help you in your work with an OS/390 computer.TSO (Time Sharing Option) is a command-driven software product which typically employs one-word or one-line commands, while SPF (System Productivity Facility) is a newer, full-screen, menu-driven product which both simplifies and extends the capabilities of TSO. ISPF allows you to perform almost all of TSO's functions by using menus and panels--and may simplify your work on the system by making it unnecessary to remember or key in longer TSO commands. Most experienced TSO/SPF users use a combination of the capabilities of TSO and SPF, choosing to use one product or the other depending on which one happens to be simpler or faster or clearer for the particular application.

One should understand that at its most basic, each TSO interactive session is actually just a special kind of batch job. It wouldn't even be that special were it not for the fact that this job communicates in an interactive session with a terminal - the one you're logged onto. The TSO batch job is an invocation of the program named IKJEFT01 - known as the Terminal Monitor Program (TMP). It should be noted that prior to TSO, mainframe processing consisted of batch work only. So the invention of a batch program that could monitor a connected device such as a display workstation was quite a significant development. This effectively opened up the machine room to a network of such terminals installed in various parts of the enterprise. Previously any work needing to be done on the mainframe was sent as punched cards and tapes to the central complex where system operators would load and execute the work on your behalf, returning the printout if you were fortunate and all ran well.

New users to the mainframe may not realize that ISPF is actually an application program that executes within a TSO environment - you can't have ISPF without TSO first. Prior to ISPF's development, programmers and system administrators would perform all their work from within the TSO (command-only) environment. Today ISPF is usually the default environment used by the developer and administrator communities in most z/OS installations. Often ISPF is automatically invoked as part of the TSO logon process and while TSO is still there under the covers many users never see or use this environment directly.

An analogy for new mainframe users would be the relationship between the old DOS and earlier versions of Windows. Although today DOS has been somewhat absorbed into the Windows graphical environment as an application you can run, earlier versions of Windows actually required DOS to be loaded prior to Windows installation. These Windows versions would use services provided by DOS and present the results in the Windows GUI. For comparative clarity, ISPF can be described as the mainframe equivalent of the Windows GUI, and TSO would be DOS - the command line.


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