System Call

API - System Call - OS Relationship

System Calls

• Programming interface to the services provided by the OS
• Typically written in a high-level language (C or C++)
• Mostly accessed by programs via a high-level Application Program Interface(API) rather than direct system call use
• Three most common APIs are Win32 API for Windows, POSIX API for PISIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

System Call Implementation

• Typically, a number associated with each system call
• System-call interface maintains a table indexed according to these numbers
• The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values
• The caller need know nothing about how the system call is implemented
• Just needs to obey API and understand what OS will do as a result call
• Most details of OS interface hidden from programmer by API
• Managed by run-time support library (set of functions built into libraries included with compiler)

Standard C Library Example

C program invoking printf() library call, which calls write() system call

참고  : Operating System Concepts by WILEY