supervisor call (SVC)

What is a supervisor call (SVC) instruction?

In computers, especially IBM mainframes, a supervisor call (SVC) instruction is a processor instruction that directs the processor to pass control of the computer to the operating system's supervisor program. Most SVCs are requests for a specific OS service from an application program or another part of the OS.

Application program developers usually use a language function or macro instruction to make the request, such as to get allocated more memory for the program to work with. The language compiler or assembler generates the instruction that includes the specific SVC request. Each service has a preassigned SVC number. When the computer's processor executes the instruction that contains the SVC, the code representing SVC causes a program interrupt to occur. This means that control of the processor is immediately passed to the OS supervisor program. The supervisor then passes control to programming that performs the service that goes with the specified SVC number.

An SVC routine is a program within the supervisor that performs the service indicated by the specific SVC instruction.