System Call:

System calls provide an interface between the processor and the operating system. System calls allow user-level processes to request some services from the operating system which process itself is not allowed to do. For example, for I/O a process involves a system call telling the operating system to read or write a particular area and this request is satisfied by the operating system.

The following different types of system calls provided by an operating system:-

Process control

end, abort
load, execute
create a process, terminate the process
get process attributes, set process attributes
wait for time
wait for the event, a signal event
allocate and free memory

File management

create a file, delete a file
open, close
read, write, reposition
get file attributes, set file attributes

Device management

request device, the release device
read, write, reposition
get device attributes, set device attributes
logically attach or detach devices

Information maintenance

get time or date, set time or date
get system data, set system data
get process, file, or device attributes
a set process, file, or device attributes

Communications

create, delete communication connection
send, receive messages
transfer status information
attach or detach remote devices