Function library call vs system call

Function library call vs system call

Function library call	System Call
In all ansi c compiler versions, C library functions are the same	System calls vary with operating systems.
It calls a program (or function) in the function library)	It calls the system kernel service.
Associate with user programs	Is an entry point of the Operating System
Run the following command in the user address space:	Run in the kernel address space
The running time belongs to "user time"	The running time belongs to the system time.
It is a process call, and the call overhead is small.	Switching between user space and kernel context is required, with high overhead
There are about 300 functions in the C function library libc	About 90 system calls in UNIX
Typical C function library call: System fprintf malloc	Typical System Call: chdir fork write BRK;