Data Compression Support

Data compression provides advantages such as the saving of disk space, reduced number of I/O operations, and reduced channel utilization. In a network it means faster data transmission and lower line costs.

z/VSE provides support for data compression (and expansion) through:
  1. The hardware instruction CMPSC which is available on all the servers that are listed in IBM Z Support.
  2. The CSRCMPSC macro which will use the hardware instruction if available; otherwise it simulates the CMPSC instruction. The CSRCMPSC macro is compatible with the MVS™ macro of the same name.
It is transparent to an application which of the two functions actually performs compression. IPL detects whether a processor supports instruction CMPSC and IPL message 0J76I informs about the compression support available.

A CMPSC application can only run if the hardware instruction is supported. A CSRCMPSC application, however, runs with the CMPSC hardware instruction if supported; if not supported the CSRCMPSC macro simulates the CMPSC instruction.

With z/VSE, you can exploit data compression as follows:
  1. Using the data compression support provided by VSE/VSAM for ESDS, KSDS, and VRDS files. This support is available on the VSE/VSAM command level as well as through the VSE/VSAM dialogs of the Interactive Interface. Further details are provided below.
  2. Using the VTAM® data compression support as introduced below.
  3. Writing or using CSRCMPSC applications as introduced below.
  4. Writing or using CMPSC applications as described in the ESA/390 Data Compression (SA22-7208).