What are system calls and system programs? Discuss the categories of system programs

Subject Introduction to Computer System
NU Year Set: 4.(d) Marks: 5 Year: 2012

System calls provide an interface between the process an 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. In handling the trap, the operating system will enter in the kernel mode, where it has access to privileged instructions, and can perform the desired service on the behalf of user-level process. It is because of the critical nature of operations that the operating system itself does them every time they are needed. For example, for I/O a process involves a system call telling the operating system to read or write particular area and this request is satisfied by the operating system.

System programs provide basic functioning to users so that they do not need to write their own environment for program development (editors, compilers) and program execution (shells). In some sense, they are bundles of useful system calls.


There are five types of systems software, all designed to control and coordinate the procedures and functions of computer hardware. They also enable functional interaction between hardware, software and the user.

Systems software carries out middleman tasks to ensure communication between other software and hardware to allow harmonious coexistence with the user.

Systems software can be categorized under the following:

Operating system: Harnesses communication between hardware, system programs, and other applications.

Device driver: Enables device communication with the OS and other programs.

Firmware: Enables device control and identification.

Translator: Translates high-level languages to low-level machine codes.

Utility: Ensures optimum functionality of devices and applications.



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