A computer system consists of hardware and software components. Hardware is the physical equipment such as the case, floppy disk drives, keyboard, monitor, cables, speakers, and printers. Computer software, also called programs, instructs the computer on how to operate. These operations may include identifying, accessing, and processing information. Essentially, a program is a sequence of instructions that describe how data is to be processed. Programs vary widely, depending on the type of information that is to be accessed or generated. For example, the instructions involved in balancing a checkbook are very different from those required to simulate a virtual reality world on the Internet.

Software is divided into two categories, operating systems and applications. Application software accepts input from the user and then manipulates it to achieve a result, known as the output. Applications are programs designed to perform a specific function directly for the user or for another application program. Examples of applications include word processors, database programs, spreadsheets, web browsers, web development tools, and graphic design tools. -

An Operating System (OS) is a program that manages all the other programs in a computer. It provides the operating environment for the applications, which is used by the applications to access resources on the computer. Operating systems perform basic tasks like recognizing input from the keyboard or mouse, sending output to the video screen or printer, keeping track of files on the drives, and controlling peripherals such as printers and modems. Disk Operating System (DOS), Windows 98, Windows 2000, Windows NT, Linux, Mac OS X, DEC VMS, and IBM OS/400 are all examples of operating systems.

Operating systems are platform-specific, meaning they are designed for use with a specific type of computer. For instance, the Windows operating system (3.1, 95, 98, 2000, or NT) is designed for use with an IBM-compatible personal computer often referred to as a PC. The Mac OS, on the other hand, will only work with Macintosh computers. PC and Macintosh are called platforms. A platform is the computer system on which programs can run.