Sunday, 20 May 2018

What is System calls in Operating System?

What is System calls in Operating System?

¡System calls provide the interface between a process and the operating system. How a program request a service from an OS’s Kernal that it does not normally have permission to run.
¡“System call provides an interface to the OS services.”
¡Application developers often do not have direct access to the system calls, but can included in the API invoke the actual system calles.By using API, Certain benefits can be gained.



System call type:

1-Process Control:

A running program needs to be able to stop execution either normally or abnormally. When execution is stopped abnormally, often a dump of memory is taken and can be examined with a debugger.

2-File Management:

Some common system calls are create, delete, read, write, reposition, or close. Also there is a need to determine the file attributes get and set file attributes. Many times the OS provides an API to make these system calls .

3-Device Management:

Process usually require several resource to execute , if these resource are available, they will be granted and control returned to the user process.
These resources are also thought of as device. Some are physical , such as a video card, and others are abstract, such as a file.
User program request the device, and when finished they release the device. Similar to files , we can read write & reposition the device.

4-Information Management:

Some system calls exist purely for transferring information between the user program & the OS. The OS also keeps information about all its processes and provides system calls to report this information.

5-Communication:

There are two model of inter-process communication, the message-passing & shared memory.
Message passing used mailbox to pass message between process. And shared memory use certain system call to create & gain access to regions of memory owned by other process.

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