Changes in CICS storage use from 31-bit to 64-bit storage

Several CICS® facilities now use 64-bit (above-the-bar) storage in the CICS region, in place of 31-bit (above-the-line) storage. These changes increase the virtual storage available for your existing and new applications to operate in 31-bit storage.

The CICS runtime environment is improved in the following ways:

The need for additional CICS regions to resolve demands on 31-bit storage is reduced.
Problems caused by short-on-storage conditions in 31-bit storage are avoided.
CICS regions can carry out simultaneous processing of a greater number of tasks that use these CICS facilities.

Conditions for CICS facilities to use 64-bit storage

In CICS TS for z/OS®, Version 4.2, some CICS facilities used 64-bit storage or 31-bit storage, depending on the version of the z/OS operating system and whether the CICS region operated with transaction isolation (set by using the TRANISO system initialization parameter). In CICS TS for z/OS, Version 5.1, these CICS facilities use 64-bit storage.

This use of 64-bit storage no longer depends on whether the CICS region operates with transaction isolation, and is supported by the version of the z/OS operating system that is required for CICS TS 5.1. For a list of CICS facilities that use 64-bit storage, see CICS facilities that use 64-bit storage.

Value for the z/OS MEMLIMIT parameter

CICS requires a MEMLIMIT value of 6 GB or higher. If you attempt to start a CICS region with a MEMLIMIT value that is lower than 6 GB, message DFHSM0602 is issued, a system dump with the dump code KERNDUMP is produced, and CICS terminates.

Main temporary storage

An additional eight fixed-length subpools (in 64-byte lengths from 576 bytes to 1024 bytes) are available for main temporary storage. These subpools can provide improvements in performance and storage for temporary storage. They are in the above-the-bar CICS dynamic storage area (GCDSA), and are named as follows:

TSMN0576
TSMN0640
TSMN0704
TSMN0768
TSMN0832
TSMN0896
TSMN0960
TSMN1024

CICS trace

CICS now uses 64-bit storage for the internal trace table, so some messages and trace points are changed.

The default size of the transaction dump trace table, set by using the TRTRANSZ system initialization parameter, is increased from 16 KB to 1024 KB.

Console queue processing

CICS now uses 64-bit storage for the console queue processing trace table and the console queue transaction entry table. These tables were previously in 31-bit storage taken from the ECDSA.

Storage allocation control blocks

CICS now uses 64-bit storage for the storage element descriptor (SCE) and free storage descriptor (SCF) control blocks, which control storage allocation. Use of 24-bit and 31-bit storage is reduced, especially in systems with a lot of storage allocation activity, for example systems with subpools that keep an element chain and that have many small records.

Loader control blocks

CICS now uses 64-bit storage for the Active Program Element (APE), Current Program Element (CPE), and CSECT descriptor control blocks in the loader domain. These control blocks were previously in 31-bit storage, and could occupy a significant amount of storage.

To provide access to the 64-bit storage, the size of the tokens used on the PROGRAM_TOKEN and NEW_PROGRAM_TOKEN options on the XPI calls ACQUIRE_PROGRAM, DEFINE_PROGRAM, and RELEASE_PROGRAM has increased from 4 bytes to 8 bytes. You must change and recompile global user exit programs that use these options. Exit programs that do not use the PROGRAM_TOKEN option or NEW_PROGRAM_TOKEN option are not affected.

Optimized access to 64-bit storage for channels and containers

Before CICS TS for z/OS, Version 5.1, CICS used dedicated copy services in the CICS Storage Manager domain to copy data to and from 31-bit and 64-bit storage. CICS components now access their 64-bit storage directly by using calls to 64-bit procedures. The new data copy functions provide improved performance, and performance is also improved because the copy services no longer require domain calls and subspace switches. CICS channels and containers, and some CICSPlex® SM components that access 64-bit storage, use the new access methods.

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Last updated: Thursday, 27 June 2019