The operating system, also known as an €œOS,€ interfaces with the computer's hardware and provides services that applications can use. Assertion (A): Every general-purpose computer must have an Operating System (OS) installed on it. OS is designed to serve two basic purposes: ?It controls the allocation and use of the computing System's resources among the various user and tasks. It provides an interface between the computer hardware and the programmer that simplifies and makes it feasible for coding, creation, debugging of application programs. Reasons (R): Man and Computer cannot communicate directly. Typically, men communicate to computers new material in the form of programs and data, requests for processing or retrieval of previously stored data or data entered from external sources, and other information required for processes performed by the computer. That is why we need OS in a computer as a man cannot directly communicate to the computer. Thus both (A) and (R) are true and (R) is the correct explanation of (A)