A computer is a device capable of performing computations and making logical dicisions at speeds millions, and even billions of times faster than human beings can. For example, many of today's personal computers can perform tens of millions of additions per second. Aperson operating a desk calculator might require decades to complete the sace mucber of calculatoins a powerful personal computer can perform in one second.(Points to ponder: How would you know whether the person added the munbers correctly? How would you know wheather the computer added the numbers correctly?) Todays fastest super- computers can perform hundreds of billions of additions per second about as many calculations as hundreds of thousands of peoplecould perform in one year! And trilloin instruction per second computers are already functioning in research laborties.

Computers process data under the control of sets of instructions called computer programs. These computer programs guide the computer through orderly sets of actions specified by the people called computer programers. The virus devises (such as the keyboard, monitor, disks, memory and processing unit) that compromise a computer system are referred to as hardware. The computer programs that run on a computer are refered to as software. soft ware costs have declined dramatically in the recent years. To the point that personal computers have become a commodity. Unfortunately, software development costs have been rising steadilu as programmers develope ever mare powerfull and complete applications, without being able to improve the technology of software development. Programming that reduce software decelopment costs would feature a sturctuted style of programming with top-downstep wise refinement , functionalization and object oriented programming: c++ is such a language regardless differences in phusical appearance, virtually eberu computer mayu be envisoned as being dividing into sex logical units or sections.

These are:
1. INPUT UNIT: This is the "recieving" section of the computer. It obtains information (data and computer programs) from various input devisees and places this information at the disposal of the other units so thar the infomation may be processed. Most information is entered into computers today through typewriter-like heyboards and "mouse"decives. in the future perhaps most information will be entered bu speaking to your computer.
2. OUTPUT UNIT:This is the "shipping" section of the computer. It takes infomation that has been processed by the computer and places it on various output devices to make the ingormation available for use outside the computer. Mast information outmut from computers today is displayed on screens, printed on paper, or used to control other devices.
3.MEMORY UNIT: this is the rapid access,relatively low-capacity "ware house" section of the computer. It retains information that has been entered through the input unit so that the ingormation may bhe made immediotely available fo r processing when it is needed. The memory unit also retains information that has already been processed until that information can be placed on output devices by the output unit. the memory unit is often called either memory of primary memory.
4. ARITHMETIC AND LOGIC UNIT. this is the "manufactoring "section of the computer. It is responsible fo rperforming calculations such as addition, subtraction, multiplication and division. It contains the devision mechanisms that allow the computer, for example, to compare two items from the memory unit to determine whether or not theu are equal.
5.CENTRAL PROCESSING UNIT. This is the "administrativ "section of the computer. It is the computer's coordenator and is reaponsible fo rsupervising the operation of the other sections. the cpu tells the input unit when information should be read into the memory unit tells the alu when information from the memory unit should be utilized in calculations and tells the output unit when tho send information from the memory unit to certain output devices.
6.SECONDARY STORAGE UNIT. this is the long term high capacity "ware house" section of the computer. programs or data mot actively being used by the other units are normally plaved on secondary storage devices (such as disks) until they are needed again, possibily hours, days, months or even years later. Information in secondary storage takes much longer to access than information in primary emory the cost per unit of secondary storage is much less than the cost per unit of primary memory.

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