Page 37 - DCAP403_Operating System

Operating System

Notes itself is not allowed to do. It is because of the critical nature of operations that the operating
system itself does them every time they are needed.

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.

The fact that improper use of the system can easily cause a system crash, thus the operating system
is introduced; it executes at the highest level of order and allows the applications to request for a
service – a system call – which is implemented through hooking interrupt(s). A system call is the
mechanism used by an application program to request service from the operating system. There
are different types of system call.

3.1 Operating System Services

The various operating system services are:
1. Program Execution
2. I/O Operations

3. File System Manipulation
4. Communications
5. Error Detection

Program Execution

The purpose of a computer systems is to allow the user to execute programs. So the operating
systems provides an environment where the user can conveniently run programs. The user does
not have to worry about the memory allocation or multitasking or anything. These things are
taken care of by the operating systems.
Running a program involves the allocating and deallocating memory, CPU scheduling in case of
multiprocess. These functions cannot be given to the user-level programs. So user-level programs
cannot help the user to run programs independently without the help from operating systems.

I/O Operations
Each program requires an input and produces output. This involves the use of I/O. The operating
systems hides the user the details of underlying hardware for the I/O. All the user sees is that the
I/O has been performed without any details. So the operating systems by providing I/O makes
it convenient for the users to run programs.

For efficiently and protection users cannot control I/O so this service cannot be provided by
user-level programs.

File System Manipulation

The output of a program may need to be written into new fi les or input taken from some fi les.
The operating systems provides this service. The user does not have to worry about secondary

storage management. User gives a command for reading or writing to a file and sees his/her task
accomplished. Thus operating systems makes it easier for user programs to accomplished their
task.
This service involves secondary storage management. The speed of I/O that depends on
secondary storage management is critical to the speed of many programs and hence I think it is

30 LOVELY PROFESSIONAL UNIVERSITY