Preview & Review: The operating system manages the basic operations of the computer. These operations include booting and housekeeping tasks. Another feature is the user interface, which may be a command-driven, menu-driven, or graphical user interface. Other operations are managing computer resources and managing files. The operating system also manages tasks, through multitasking, multiprogramming, time-sharing, or multiprocessing.
The operating system (OS) consists of the master system of programs that manage the basic operations of the computer. These programs provide resource management services of many kinds, handling such matters as the control and use of hardware resources, including disk space, memory, CPU time allocation, and peripheral devices. The operating system allows you to concentrate on your own tasks or applications rather than on the complexities of managing the computer.
Different sizes and makes of computers have their own operating systems. For example, Cray supercomputers use UNICOS and COS, IBM mainframes use MVS and VM, Data General minicomputers use AOS and DG, and DEC minicomputers use VAX/VMS. Pen-based computers have their own operating systems—PenRight, PenPoint, Pen DOS, and Windows for Pen Computers that enable users to write scribbles and notes on the screen. These operating systems are not compatible with one another. That is, in general, an operating system written for one kind of hardware will not be able to run on another kind of machine.
Microcomputer users may readily experience the aggravation of such incompatibility when they buy a new microcomputer. Should they get an Apple Macintosh with Macintosh Systems Software, which won't run IBM-compatible programs- Or should they get an IBM or IBM-compatible (such as Compaq, Dell, or Zenith), which won't run Macintosh programs? And, if the latter, should they buy one with DOS with Windows, Windows 95, OS/2, Windows NT, or Unix? Should they also be concerned with an operating system such as NetWare that will link several computers on a local area network? Should they wait for a new operating system to be introduced that may resolve some of these differences?
Before we try to sort out these perplexities, we should see what operating systems do that deserves our attention. We consider:
• Housekeeping tasks
• User interface
• Managing computer resources
• Managing files
• Managing tasks
The operating system begins to operate as soon as you turn on, or "boot," the computer. The term booting refers to the process of loading an operating system into a computer's main memory from diskette or hard disk. This loading is accomplished by a program (called the bootstrap loader or boot routine) that is stored permanently in the computer's electronic circuitry. When you turn on the machine, the program obtains the operating system from your diskette or hard disk and loads it into memory. Other programs called diagnostic routines also start up and test the main memory, the central processing unit (/ p. 16), and other parts of the system to make sure they are running properly. As these programs are running, the display screen may show the message "Testing RAM" (main memory). Finally, other programs (indicated on your screen as "BIOS," for basic input-output system) will be stored in main memory to help the computer interpret keyboard characters or transmit characters to the display screen or to a diskette.
All these activities may create a jumble of words and numbers on your screen for a few seconds before they finally stop. Then a guide may appear, such as "A:\>" or "C:\>." This is the system prompt. The system prompt indicates the operating system has been loaded into main memory and asks ["prompts") you to enter a command. You may now enter a command. The operating system remains in main memory until you turn the computer off. With newer operating systems, the booting process puts you into a graphically designed starting screen, from which you choose the applications programs you want to run.
If you have not entered a command to start an applications program, what else can you do with the operating system? One important function is to perform common repetitious "housekeeping tasks."
One example of such a housekeeping task is formatting blank diskettes. Before you can use a new diskette that you've bought at a store, you may have to format it. Formatting, or initializing, electronically prepares a diskette so it can store data or programs. (On IBM-style computers, for example, you might insert your blank disk into drive A and type the command Format a:. You can also buy preformatted disks.)