System calls provide an interface between processes and the operating system. They allow programs to request services like reading/writing files or communicating over a network. Common system calls include opening/closing files, reading/writing data, process creation/termination, and requesting the current time/date. System calls are grouped into categories like process control, file management, device management, information maintenance, and communications.

2. System call provide the interface between a process and the operating system. Certain system allow system calls to be made directly from a higher level language program, the calls normally resembles predefined functions or subroutine calls. They may generate a call to a special run-time routine that makes the system calls, or the system call may be generated directly in line. These calls generally available as assembly language instructions.

3. Example:- Consider that we have to write a program to read data from one file and to copy them to another file. The first input that the program will need is the names of the two files the input file and the output file. In an interactive system this approach will require a sequence of system calls first to write a prompting message on the screen and then to read from the keyboard the characters that define the two files. After file names are obtained each

4. Of these operations require another system calls and may encounter possible error conditions. X: Parameters for call Load address X System call 13 Use Parameters from table X X User Program Operating System

5. System Call can be grouped into five major categories Process Control File Management Device Management Information Maintenance Communications

6. Process Control END, ABORT Load, Execute Create Process, Terminate Process Wait Event, Signed Event Allocate and free memory

7. File Management Create File, Delete File Open , Close Read, write, reposition Get file attributes, set file attributes

8. Device Management Request device, Release Device Read, Write, Reposition Get Device attributes, set device attributes Logically attach or detach device

9. Information Maintenance Get time or date, set time or date Get system date, set system date Get process, device attributes

10. Communications Create, delete communications connections Send, Receive message Transfer status information Attach or detach remote devices

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