System Calls

• System calls provide the interface between a running program and the operating system.

1. Generally available as assembly-language instructions.
2. Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++)

• Three general methods are used to pass parameters between a running program and the operating system.

1. Pass parameters in registers.
2. Store the parameters in a table in memory, and the table address is passed as a parameter in a register.
3. Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.