C Library


The system call interface is a little too low-level
Actually, C language is too low-level as well

The system, thus, usually includes a standard C library
It implements a function-call API for the hw-specific syscall mechanism
It offers file I/O with buffering (it helps system calls)
It offers string operations (it helps C language)
It gives names to numbers, by accessing system files (it adds policy)

The system library is called "C" library but it isn't specific to C.
Most programs, most languages, rely on libc for their work
There are several implementations of the library, both big and small
You can write your own C library, and it's fun
There also exist programs that do not use libc, and it's fun

The POSIX standard covers most abstraction levels
Both system calls and standard library, for example.