The operating system provides two interfaces to the user: the command interface and the system call.
Differences:
1. Different users
Command interface: the system provides for the user.
System calls: programmers use system calls.
2, the operation process is different
Command interface: the use of operational commands to organize and control the execution of operations or management of computer systems.
System call: requesting the operating system to provide services, such as applying for and releasing peripherals and other types of resources, control the speed of execution of the program.
Difference between system call and ordinary call
1, running state is different
System call the calling process and the called process running in different states, while the ordinary procedure call generally run in the same state.
2. Different calling methods
System calls must first enter the system core through a soft interrupt mechanism before turning to the corresponding command handler. Ordinary procedure calls can be directly from the calling process to the called process.
3. Return Issues
In systems with preemptive scheduling, when a system call returns, the scheduling analysis is repeated -- whether a higher-priority task is ready. Ordinary procedure calls return directly to the calling procedure to continue execution.