The first generation (1945 to 1955):

It was the time before the Second World War when the digital computer was not developed, and there were calculating engines with mechanical relays at this point in time. Later mechanical relays were replaced by vacuum tubes as they were very slow. But, the performance issue was not resolved even with vacuum tubes, besides these machines were too bulky and large as there were made of tens of thousands of vacuum tubes.

Furthermore, each of the machines was designed, programmed, and maintained by a single group of people. The programming languages and operating systems were not known, and absolute machine language was being used for programming.

These systems were designed for numerical calculations. The programmer was required to sign up for a block of time and then insert his plug board into the computer. In the 1950s, punch cards were introduced, which improved the computer performance. It allowed programmers to write programs on punch cards and read them into the system; the rest of the procedure was the same.

The second generation (1955 to 1965):

This generation started with the introduction of transistors in the mid-1950s. The use of transistors made the computers more reliable, and they began to be sold to customers. These machines were called mainframes. Only the big organization and government corporations could afford it. In this machine, the programmer was required to write the program on a paper then punch it on cards. The card would be taken to the input room and handed over to an operator to get the output. The printer provides the output which was taken to the output room. These steps made it a time-consuming task. So, the batch system was adopted to address this issue.

In a batch system, the tasks were collected in a tray in the form of batches in the input room and read onto a magnetic tape, which was taken to the machine room, where it was mounted on a tape drive. Then using a special program, the operator was to read the first task or job from the tape and run it, and the output was generated onto a second tape. OS automatically read the next job from the tape, and Jobs were completed one by one. After the completion of the batch, the input and output tapes were taken off, and the next batch was started. The printouts were taken from the output tape. It was mainly used for engineering and scientific calculations. The first OS was used in this generation in computers was called FMS (Fortran Monitor System), and IBMSYS, and FORTRAN were used as a high-level language.

The third generation (1965 to 1979):

This generation began with the introduction of 360 family of computers of IBM in 1964. In this generation, transistors were replaced by silicon chips, and the operating system was developed for multiprogramming, some of them even supported batch processing, time sharing, real-time processing, at the same time.

The fourth generation operating system (1979 to Present):

This generation of OS started with the introduction of personal computers and workstations. Chips that contain thousands of transistors were introduced in this generation that made possible the development of personal computers that supported the growth of networks and thus the development of network operating systems and distributed operating systems. DOS, Linux, and window operation systems were are few examples of OS of this generation.