SVC
Supervisor call: the instruction a program uses to ask z/OS to do something for it, such as open a file or get storage.
Also written supervisor call, SVC instruction, SVC number
An SVC, or supervisor call, is the way a program asks z/OS for a service that it cannot perform itself. The program issues the SVC instruction with a number, and z/OS takes over, does the work with its own authority, and returns.
Each number is a different service. Some deal with storage, some with opening and closing files, some with loading programs and some with ending a task. Programmers rarely code SVCs by number. They use macros, and the macros contain the SVC instructions.
SVC numbers show up in other places. Some abend codes are tied to the service that failed, and dumps and traces list the SVCs a program issued before it failed. System programmers sometimes install their own SVCs, which is a sensitive change because the code runs with full authority.
For most people, the term matters only when reading dumps or diagnostic output. It is enough to know that an SVC is a request from a program to the operating system.
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- AssemblerThe low-level programming language of the mainframe, where each statement matches a single machine instruction.
- z/OSThe main operating system that runs on IBM mainframes, in the same way Windows or Linux runs on a laptop or server.
- DumpA copy of a program's memory taken at the moment it failed, used to find out why.
- AbendAn abnormal end: a program stopping in an uncontrolled way rather than finishing and reporting a result.
- APF authorisationThe Authorized Program Facility: the z/OS rule that only programs from approved libraries may use the system's most powerful functions.
- PSWProgram status word: the processor's record of what it is doing, including the address of the next instruction, shown in abend messages and dumps.