An operating system is a program that manages the computer hardware. Operating system acts as an intermediary between the computer hardware and the user and also provides a basis for application programs. An astonishing aspect of operating system is how varied they are in achieving these tasks for the computer. Mainframe operating systems are intended first and foremost to optimize consumption of hardware. Personal computer operating systems support complex business applications, games and everything in between the user and hardware. This is the basic need of a computer to be run because the instructions are directly given to the hardware with the help of operating system.
The operating system is a large and complex set of instructions therefore it must be created piece by piece so that the problem which comes in the development of software can be handled and should be take care of. Each of the pieces should be well defined in context to the system which carefully defines the input, output, and the functions given by the user to the hardware.
For use in hand-held computers the operating systems are designed in sequence to provide the environment in which the user can easily interface with the hardware to execute the various programs. Therefore some of the operating systems are designed to be convenient with the user, others to be efficient with the users and some of them are designed as the combination of both of them. The operating system is a software or asset of instructions that intimately involve with the hardware to execute the different types of operations given by the user. Therefore we can also say the operating system as a resource allocator which allocates all the resources needed by the hardware to accomplish the command provided by the user. Operating system is especially concerned with the operation and control of I/O devices.