SVC routines

If you are writing an SVC, use the information here in conjunction with “User-Written SVC Routines” in z/OS MVS Programming: Authorized Assembler Services Guide. There are five types of SVC routines, which are distinguished as follows:

Residence

SVC types 1, 2, and 6 are part of the nucleus.
SVC types 3 and 4 reside in the link pack area (LPA).
A type 3 routine is a single load module, while a type 4 routine consists of two or more load modules.