WHAT IS AN OPERATING SYSTEM?

An Operating System (often referred to as OS) is an integrated set of programs that controls the resources (CPU, memory, I/O devices, etc.) of a computer system and provides its users with an interface or virtual machine that is easier to use than the bare machine. According to this definition, the two primary objectives of an operating system are:

1. Make computer system easier to use. A computer system consists of one or more processors, main memory, and many types of I/O devices such as disks, tapes, terminals, network interfaces, etc. Writing programs for using these hardware resources correctly and efficiently is an extremely difficult job, requiring in-depth knowledge of the functioning of these resources. Hence, to make computer systems usable by a large number of users, it became clear several years ago that computer systems need some mechanism to shield programmers and other users from the complexity of hardware resources. Researchers gradually evolved a solution to handle this problem by putting a layer of software on top of bare hardware. This layer of software manages all hardware resources of the system and presents the users with an interface or virtual machine that is easier, safer, and efficient to program and use. It is called the operating system.
          The below figure shows the logical architecture of a computer system. As shown, the operating system layer surrounds hardware resources. Then a layer of other system software (such as compilers, editors, utilities, etc.) and a set of application programs (such as commercial data processing applications, scientific and engineering applications, entertainment, and educational applications, etc.) surrounds the operating system layer. Finally, end-users view the computer system in terms of the interfaces of the application programs. 
   
   
   
   
   
   
   
2. Manage the resources of a computer system. An operating system manages all the resources of a computer system. This involves performing such tasks as keeping track of who is using what resources, granting resource requests, accounting for resource usage, mediating conflicting requests from different programs and users. Efficient and fair sharing of system resources among users/or programs is a key goal of all operating systems.