Operating system (OS) programs are essential for the computer’s functionality, without which, the computer is a useless machine. The OS is also known as a software environment or platform. It is safe to say is that is the most important program on a computer. Primarily, OS controls the hardware and software of the computer in which located, increasing the flexibility of the computer’s uses. This characteristic includes recognizing input from different hardware, keyboard or mouse, and processing it to create output, which is displayed on the monitor, expressed by printing and many other tasks. These features are carried on due to the presence of operating system files known as Kernel, which are copied into the computer memory when the computer is first switched on, hence represent the central component of the computer OS. The OS also organizes and locates various computer files on a storage disk. Subsequently, the user interacts with the hardware and software through the user interface provided by the OS. The command of copying a file is completed by the OS accepting the command then executing it, this OS feature is known as the command processor. A feature provided by the OS is the Graphical User Interface (GUI), which is responsible for allowing interaction between the user and the computer and access to programs via clicking on graphics, represented in the form of icons. Moreover, applications can be run and downloaded by OS.

OS must be chosen wisely due to their software platform characteristic. A software platform has specific applications designed to run on it, hence, the OS must be chosen accordingly. OS can also be distinguished according to their specifications. Multi-user feature of the OS allows two or more users to run programs at the same time. This feature allows each user to completely personalize their window. Moreover, there are multi-processing OS, which support running the same program on more than one CPU. Multi-tasking, on the other hand, is a feature that allows the running of more than one program at the same time, and the alternating usage of these programs. Real-time processing is a feature that allows the instantaneous processing of input, providing instant response. This feature contributes to the speeding up of tasks performed by the computer. An OS could have one, most, or all of these features; all is dependent on individual or corporation use.

Although these features are essential differentiation means, the most basic and widely used mean of differentiation between OS is according to the computers in which they are used. Hence, OS are categorized into stand-alone OS, network OS, and embedded OS.

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