Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. Windows, Linux, Unix, and DOS are examples of popular OSs. Clock speed is measured in megahertz. 200 MHz equals 200 million cycles a second.
Clock speed is to a computer as horse power is to the engine of car.
More meaningful information is obtained by combining consecutive bits into larger units. For example, a byte is composed of 8 consecutive bits. On almost all modern computers, a byte is equal to 8 bits. A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information. The amount of data that can be transmitted in a fixed amount of time.