Syscalls

System Calls

System calls are how programs that users initiate request resources from the OS kernel. This design is supposed to give the OS control over the system, or a means of regaining control from the processes it initiates.

What a system call is to the Operating System is defined by an interface which provide a series of functions that raise "interrupts," pieces of code that causes to kernel to take over and operate according to some specially-set registers that the function should set up before interrupting.

Depending on the system call, completing the interupt may require more time than simple code execution time. If a call requires input from the user, or a response from another piece of hardware, then the kernel has no choice but to wait for this response. The process that made the call is considered "blocked," and forced to wait until the desired information arrives to finish its execution. In a well-scheduled OS, other processes will continue to run, and the system will continue to operate until the information is presented, which causes another interrupt that properly finishes the prior system call.