What Is An Operating System?

• An OS is software that manages the computer hardware.
  • Mainframe OSs are designed primarily to optimize utilization of hardware.
  • Personal computer (PC) OSs support complex games, business applications, and everything in between.
  • OSs for handheld computers are designed to provide an environment in which a user can easily interface with the computer to execute programs.
• Thus, some OSs are designed to be convenient, others to be efficient, and others some combination of the two.

  Figure 2.1: Abstract view. Where the OS fits in.
• A computer system can be divided roughly into four components: the hardware, the OS, the application programs, and the users (see Fig. 2.1).
  1. Hardware
     • Electronic, mechanical, optical devices.
     • The central processing unit (CPU), the memory, and the input/output (I/O) devices-provides the basic computing resources for the system.
     • The hardware must provide appropriate mechanisms to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.
  2. Software
     • Programs. Without support software, a computer is of little use. With its software, however, a computer can store, manipulate, and retrieve information.
     • Software can be grouped into the following categories:
       • systems software (OS & utilities)
       • applications software (user programs; word processors, spreadsheets, compilers, database systems, games, web browsers etc.)
• As a summary;
  • Hardware provides basic computing resources (CPU, memory, I/O devices).
  • OS controls and coordinates the use of the hardware among the various application programs for the various users.
  • Provides orderly and controlled allocation (i.e., sharing, optimization of resource utilization) and use of the resources by the users (jobs) that compete for them.
• An OS is similar to a government. Like a government, it performs no useful function by itself. It simply provides an environment within which other programs can do useful work.