CICS application programs

Online application programs have certain features and needs in common. Typically, they:

* Serve many online users, apparently simultaneously.
* Require common access to the same data sets and databases.
* Try to give each end user a timely response to each interaction.
* Involve telecommunications access to remote terminals.

The host operating system is in overall charge of the computer and manages resources in whatever way you set up. But the very versatility of a general-purpose operating system means that it often cannot give online programs the sort of priority treatment they need. Instead, CICS may be given "privileged" treatment on behalf of all the online programs that run under it.

To make the best use of the time and system resources that the operating system gives to CICS, CICS takes on itself some of the aspects of an operating system. For example, CICS allows more than one of its programs (tasks) to be in an active state at the same time. But CICS doesn't duplicate all of the services provided by the operating system. Whenever appropriate, CICS goes straight to the operating system to provide what its tasks ask for.

What does CICS do?

CICS controls online DB/DC application programs. But what does this mean? In fact, it means that CICS is a program that does a lot of work on your behalf. CICS handles interactions between terminal users and your application programs. An interaction may consist of one or more requests from, and responses to, a terminal user in the course of a single job by that user.

CICS provides:

The functions required by application programs for communication with remote and local terminals and subsystems

Control of concurrently running programs serving many online users Facilities for accessing databases and files, in conjunction with the various IBM database products and data access methods that are available

The ability to communicate with other CICS systems and database systems, both in the same computer and in connected computer systems.

IBM has left things as open as possible to allow customers to produce the system they need. It's up to your systems and applications designers (which could mean you, of course) to choose what they want from the various CICS facilities, and to build whatever kind of user interface that best suits the end users. So, although you still have to provide the application programs that the end users actually run, CICS makes it much easier. Your programs gain access to the CICS facilities they need by straightforward, high-level, commands.

What is CICS?

CICS (Customer Information Control System) is a general-purpose data communication system that can support a network of many hundreds of terminals. You may find it helpful to think of CICS as an operating system within your own operating system (although this definition might offend purists). In these terms, CICS is a specialized operating system whose job is to provide an environment for the execution of your online application programs, including interfaces to files and database products.