SVC (SuperVisor Call)is an RR type instruction in which the two register address fields are not utilized for register address, but contain a one byte numeric code(N) that identifies the purpose of SVC.
where N - a decimal integer from 0 to 255.
When SVC is executed :
- Control is transferred to a fixed location within the operating system.
- the address of the instruction following the SVC is preserved so that the operating system can return control to the user program following completion of the task being requested.
- the state of the computer system is set to supervisor mode so that privileged instructions may be executed while the operating system is performing the task.
- the SVC operand is made available to the operating system through the interruption code field of the program status word.
The operating system determines the purpose of the SVC by examining the SVC operand code and proceeds accordingly.
eg: SVC 13 - means ABEND
SVC 8 --LOAD
SVC 9 -- DELETE etc...