The interface between a process and an operating system is provided by system calls. In general, system calls are available as assembly language instructions. They are also included in the manuals used by the assembly level programmers.
System calls are usually made when a process in user mode requires access to a resource. Then it requests the kernel to provide the resource via a system call.
There are mainly five types of system calls. These are explained in detail as follows −
Here are the types of system calls −
These system calls deal with processes such as process creation, process termination etc.
These system calls are responsible for file manipulation such as creating a file, reading a file, writing into a file etc.
These system calls are responsible for device manipulation such as reading from device buffers, writing into device buffers etc.
These system calls handle information and its transfer between the operating system and the user program.
These system calls are useful for interprocess communication. They also deal with creating and deleting a communication connection.
Some of the examples of all the above types of system calls in Windows and Unix are given as follows −
|Types of System Calls||Windows||Linux|
There are many different system calls as shown above. Details of some of those system calls are as follows −
In some systems, a process may wait for another process to complete its execution. This happens when a parent process creates a child process and the execution of the parent process is suspended until the child process executes. The suspending of the parent process occurs with a wait() system call. When the child process completes execution, the control is returned back to the parent process.
This system call runs an executable file in the context of an already running process. It replaces the previous executable file. This is known as an overlay. The original process identifier remains since a new process is not created but data, heap, stack etc. of the process are replaced by the new process.
Processes use the fork() system call to create processes that are a copy of themselves. This is one of the major methods of process creation in operating systems. When a parent process creates a child process and the execution of the parent process is suspended until the child process executes. When the child process completes execution, the control is returned back to the parent process.
The exit() system call is used by a program to terminate its execution. In a multithreaded environment, this means that the thread execution is complete. The operating system reclaims resources that were used by the process after the exit() system call.
The kill() system call is used by the operating system to send a termination signal to a process that urges the process to exit.However, kill system call does not necessary mean killing the process and can have various meanings.