TODAY's DISCUSSION ON MAINFRAMES

NOTION OF LOGICAL LEVELS WITH LINK XCTL AND RETURN!!

The CICS Terminal Control is the highest level and is considered to be running at LEVEL 0.The first initiated one by entering the TRAN-ID is said to be at LEVEL 1. If PROGRAM-A at LEVEL 1 is calling PROGRAM-B using the LINK command, then PROGRAM-B is considered to be at LEVEL 2 as both PROGRAM-A and PROGRAM-B will both be loaded in MAIN STAORAGE. If PROGRAM-C is called by PROGRAM-A using the XCTL command, then, PROGRAM-C is said to be at LEVEL 1 as PROGRAM-A will be removed from MAIN STORAGE after loading PROGRAM-C. The options that are used with LINK and XCTL commands are PROGRAM, COMMAREA and LENGTH. RETURN command is used to transfer control from one logical level to the level one above it.A RETURN command at logical LEVEL 1 (only at LEVEL 1) can have the options TRANSID, COMMAREA and LENGTH to initiate a new TRANSACTION once the control is passed to the CICS.The RETURN command at all other logical levels should be issued without any options.

SOME MORE DOSE

LINK is used to transfer control from an application program at one logical level to an application program at the next lower logical level. If the LINKED to program is not already in the MAIN storage, it will be loaded. When the RETURN command is executed in the LINKED to program, control is returned to the program initiating the LINKAGE at the next sequential executable instructions. XCTL is used to transfer control from one application program to another application at the same logical level. The program which control is transferred is released. If the program to which control is transferred is not already in the memory, it will be loaded.

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