Operating system plays important role in computer. Without Operating system computer cannot run. it will be just a dead machine. Operating system manage a computer's resources- memory, pheripherial devices, and even cpu access and provide a battery of services to the user's programs. UNIX, first developed for micro computers and now widely used on both pcs and mainframes is one example.
In early days computer had no operating system. A user loaded a program from paper tape by employing switches to specify it's memory address, to start loading, and to run the program. when the program finished, the computer halted. the programmer had to have knowledge of every compuer detail, such as how much memory it had and the characteristics of I/o devices used by the program. It was quickly realized that this was an inefficient use of resources, particularly as the cpu was largely idle while wating for relatively slow I/o devices to finished tasks such as reading and writing data. if instead several programs could be loaded at once and coordinated to interleave their step of computation and I/o, more work could be done. The earliest operating system were small supervisor programs that did just that they coordinated several programs, accepting commands from the operator and provided them all with basic I/o operation. These were known as multiprogrammed system.