IMS SVC modules

IMS uses a Type 2 supervisor call (SVC), in the range of 200-255, for batch, utility, DBCTL, DCCTL, and DB/DC IMS control program functions. IMS uses a Type 4 supervisor call (SVC), in the range of 200-255, for DBRC functions.

If you are installing different versions of IMS in the same z/OS® system, note that the Type 2 SVC and Type 4 SVC are downward compatible. The SVC module for IMS 15 can be used by IMS Version 13 and IMS 14. However, the SVC module for IMS Version 13 cannot be used by IMS 14 or IMS 15, and the SVC module for IMS 14 cannot be used by IMS 15.
Note: The IMS V15 SVC module is the same in all levels of IMS 15. You do not need to reinstall the IMS 15 SVC if you migrate from previous IMS 15 release levels, such as IMS 15.2, to IMS 15.3.
Important: If you specify the SVC2= or SVC4= parameters in the DFSIDEF0 module, ensure that the DFSIDEF0 module resides in an APF-authorized library that is included in the IMS Control Region JOBLIB or STEPLIB concatenation, or in the z/OS LINKLIST concatenation.

Type 2 SVC

Perform the following steps to use the type 2 SVC:
  1. Define a type 2 SVC number by specifying the SVC2= keyword in one of the following locations. If you do not use the SVC2= keyword to define a type 2 SVC number, IMS uses a default value of 254.
    Important: If you use the Open Database Access (ODBA) interface or the database resource adapter (DRA) and you do not want to use the default value of 254 for the type 2 SVC number, you can define the number only by using the DFSIDEF macro of the DFSIDEF0 module.
    • In the DFSPBxxx member of the IMS PROCLIB data set. The value that you specify in the DFSPBxxx member overrides the value that is specified on the DFSIDEF macro.
    • In JCL. The value that you specify in JCL overrides the SVC2= keyword value that is specified in the DFSPBxxx member and the value that is specified on the DFSIDEF macro.
    • On the DFSIDEF macro of the DFSIDEF0 module by specifying the following code: 
      DFSIDEF TYPE=PARM,SVC2=
      The value that is specified on the DFSIDEF macro is overidden by the value that is specified in the DFSPBxxx member or in JCL.
  2. If you used the SVC2= parameter on the DFSIDEF macro to define a type 2 SVC number, assemble and link the DFSIDEF0 module into IMS.SDFSRESL.
  3. Run JCL to re-link the type 2 SVC routine, DFSVC200, as IGCxxx, where xxx is the type 2 SVC number. To generate sample JCL for re-linking the routine, specify TYPE=GEN,SVC2=xxx on the DFSIDEF macro.
    Important: If you specify TYPE=GEN on the DFSIDEF macro, you cannot use another form of the TYPE= statement on the macro.
  4. Bind the type 2 SVC routine into the z/OS nucleus.

Type 4 SVC

Perform the following steps to use the type 4 SVC:
  1. To define a type 4 SVC number, specify the following code on the DFSIDEF macro of the DFSIDEF0 module. If you do not use the SVC4= keyword to specify a type 4 SVC number, IMS uses a default value of 255.
    DFSIDEF TYPE=PARM,SVC4=
  2. Assemble and link the DFSIDEF0 module into IMS.SDFSRESL.
  3. Run JCL to re-link the type 4 SVC routine, DSP00MVS, as IGC00yyy, where yyy is the EBCDIC representation of the zoned-decimal type 4 value. You can use the sample JCL, which is generated when you specify TYPE=GEN,SVC4=yyy on the DFSIDEF macro, to re-link the routine.
    Important: If you specify TYPE=GEN on the DFSIDEF macro, you cannot use another form of the TYPE= statement on the macro.
  4. Bind the type 4 SVC routine in an LPA or MLPA library.

Defining the IMS and DBRC SVCs to z/OS

When you define the IMS and DBRC SVCs to z/OS, follow this format:

Example:

SVCPARM 254,REPLACE,TYPE(2)
SVCPARM 255,REPLACE,TYPE(4)

Related reading: Refer to z/OS MVS Initialization and Tuning Reference for information on defining SVCs to z/OS.