System Calls Versus Library Calls

An operating system is fundamentally a way to abstract the hardware into a set of calls you can make from your program. These calls run in the kernel and are the only way to interface with the hardware. They are very different from calls you may make to libraries, though from a programming point of view they look similar.

The original Unix system calls were read, write, open, creat (sic), close, fork, exec, wait, and exit. Dennis Ritchie gives a good explanation of what was done and why in “The Evolution of the Unix Time-sharing System” at http://cm.bell-labs.com/cm/cs/who/dmr/hist.html.