Unable to start debugging on the web server - Chapter 1 Introduction to Computers, the Internet and
Chapter 1 Introduction to Computers, the Internet and the Web 47 The various devices that comprise a computer system (such as the keyboard, screen, disks, memory and processing units) are referred to as hardware. The computer programs that run on a computer are referred to as software. The input unit is the receiving section of the computer. It obtains information (data and computer programs) from various input devices and places this information at the disposal of the other units so that the information may be processed. The output unit is the shipping section of the computer. It takes information processed by the computer and places it on output devices to make it available for use outside the computer. The memory unit is the rapid access, relatively low-capacity warehouse section of the computer. It retains information that has been entered through the input unit so that the information may be made immediately available for processing when it is needed and retains information that has already been processed until that information can be placed on output devices by the output unit. The arithmetic and logic unit (ALU) is the manufacturing section of the computer. It is responsible for performing calculations such as addition, subtraction, multiplication and division and for making decisions. The central processing unit (CPU) is the administrative section of the computer. It is the computer s coordinator and is responsible for supervising the operation of the other sections. The secondary storage unit is the long-term, high-capacity warehousing section of the computer. Programs or data not being used by the other units are normally placed on secondary storage devices (such as disks) until they are needed, possibly hours, days, months or even years later. Early computers were capable of performing only one job or task at a time. This form of computer operation often is called single-user batch processing. Software systems called operating systems were developed to help make it more convenient to use computers. Early operating systems managed the smooth transition between jobs and minimized the time it took for computer operators to switch between jobs. Multiprogramming involves the simultaneous operation of many jobs on the computer the computer shares its resources among the jobs competing for its attention. Timesharing is a special case of multiprogramming in which dozens or even hundreds of users share a computer through terminals. The computer runs a small portion of one user s job, then moves on to service the next user. The computer does this so quickly that it might provide service to each user several times per second, so programs appear to run simultaneously. An advantage of timesharing is that the user receives almost immediate responses to requests rather than having to wait long periods for results, as with previous modes of computing. In 1977, Apple Computer popularized the phenomenon of personal computing. In 1981, IBM introduced the IBM Personal Computer. Almost overnight, personal computing became legitimate in business, industry and government organizations. Although early personal computers were not powerful enough to timeshare several users, these machines could be linked together in computer networks, sometimes over telephone lines and sometimes in local area networks (LANs) within an organization. This led to the phenomenon of distributed computing, in which an organization s computing is distributed over networks to the sites at which the real work of the organization is performed. Today, information is shared easily across computer networks where some computers called file servers offer a common store of programs and data that may be used by client computers distributed throughout the network hence the term client/server computing. Java has become the language of choice for developing Internet-based applications (and for many other purposes). Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/8/01
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