Advanced CICS for Senior Software Developers(1 of 5)

Many CICS-Mainframe programmers do not know exact difference between ATI and START. Understanding these concepts is little tricky. That is why I am posting these concepts for Senior software developers.

Since CICS has multitasking capability, let us see how it initiates different tasks.


Automatic time ordered transaction initiation, or time ordered ATI, is a CICS facility lets you start a new task by issuing a START command from a program.

START==> Will initiate new task in layman terms.

Before you understand ATI, you need to understand the difference between starting a task, and using the program control commands (LINK or XCTL) to invoke a program.

As a multitasking system, CICS can process more than one task at a time.

As a result, a task initiated by a START command can execute simultaneously with the task that issued the START command. In other words, the starting task can run at the same time as the started task.

In contrast, programs invoked by LINK and XCTL commands run one at a time as part of a single task.

To illustrate, consider how you might use program control and interval control commands in a menu driven application that includes a data entry program that requires user interaction and a report preparation program that doesn’t.

When a user selects the data entry program, the menu program should issue an XCTL command to transfer control directly to that program. If the user selects the report preparation program, though, the menu program should issue a START command to start the program as a separate task. Then, control returns to the menu program, and the user can continue other work while the report is being prepared.

Final Notes:

  • A task that is initiated by START is asynchronous. No need to wait for instant reply. It is a separate task CICS initiated. So user can proceed with other tasks.

-Program invoked by LINK and XCTL, are synchronous, that means user has to wait till gets reply from program

Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.