|CICS is able to
handle simultaneous execution of many tasks.
This ability to handle many simultaneous tasks is known as
|For CICS a task is
the running of a set of programs as a unit to form a transaction.
|To start a
transaction, a four character code known as the TRANS-ID is entered. In an interactive session a user types this
TRANS-ID in at a terminal and presses the Enter key.
|The TRANS-ID is sent
to the Program Control Table (PCT) which contains a translation of the four
character code to a program name.
|Assuming that the
TRANS-ID is valid, CICS checks the Processing Program Table (PPT) to find
where the program resides. The program
may already reside in memory, in which case execution begins. If the PPT shows that the program is on
disk, the executable version of the program, known as the LOAD MODULE, is
retrieved from disk and loaded into memory.
Once inside of the CICS memory area, known as the ADDRESS SPACE, the
program runs and the transaction completes.