Computer Basics Lecture Notes

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  Computer Basics What is a Computer? A computer is an electronic machine that accepts information, stores it until the informationis needed, processes the information according to the instructions provided by the user, andfinally returns the results to the user. The computer can store and manipulate large quantitiesof data at very high speed, but a computer cannot think. A computer makes decisions basedon simple comparisons such as one number being larger than another. Although the computer can help solve a tremendous variety of problems, it is simply a machine. It cannot solve problems on its own. History of Computers Since civilizations began, many of the advances made by science and technology havedepended upon the ability to process large amounts of data and perform complemathematical calculations. !or thousands of years, mathematicians, scientists and businessmen have searched for computing machines that could perform calculations andanalyze data quickly and efficiently. ne such device was the abacus.The abacus was an important counting machine in ancient #abylon, $hina, and throughout%urope where it was used until the late middle ages. It was followed by a series of improvements in mechanical counting machines that led up to the development of accuratemechanical adding machines in the &'()*s. These machines used a complicated assortmentof gears and levers to perform the calculations but they were far to slow to be of much use toscientists. Also, a machine capable of making simple decisions such as which number islarger was needed. A machine capable of making decisions is called a computer.The first computer like machine was the +ark I developed by a team from I#+ and arvard-niversity. It used mechanical telephone relays to store information and it processed dataentered on punch cards. This machine was not a true computer since it could not makedecisions.In une &'/(, work began on the world0s first electronic computer. It was built at the-niversity of 1ennsylvania as a secret military pro2ect during 3orld 3ar II and was to beused to calculate the tra2ectory of artillery shells. It covered &4)) square feet and weighed ()tons. The pro2ect was not completed until &'/5 but the effort was not wasted. In one of itsfirst demonstrations, the computer solved a problem in 6) seconds that took a team of mathematicians three days. This machine was a vast improvement over the mechanicalcalculating machines of the past because it used vacuum tubes instead of relay switches. Itcontained over &7,))) of these tubes, which were the same type tubes used in radios at thattime. The invention of the transistor made smaller and less epensive computers possible.Although computers shrank in size, they were still huge by today*s standards. Another innovation to computers in the 5)*s was storing data on tape instead of punch cards. Thisgave computers the ability to store and retrieve data quickly and reliably.    Classification of Computersi.Mainframe Computersii.Minicomputersiii.Microcomputersiv.Supercomputers +ainframe computers are very large, often filling an entire room. They can store enormousof information, can perform many tasks at the same time, can communicate with many usersat the same time, and are very epensive. . The price of a mainframe computer frequentlyruns into the millions of dollars. +ainframe computers usually have many terminalsconnected to them. These terminals look like small computers but they are only devices usedto send and receive information from the actual computer using wires. Terminals can belocated in the same room with the mainframe computer, but they can also be in differentrooms, buildings, or cities. 8arge businesses, government agencies, and universities usuallyuse this type of computer.+inicomputers are much smaller than mainframe computers and they are also much lessepensive. The cost of these computers can vary from a few thousand dollars to severalhundred thousand dollars. They possess most of the features found on mainframe computers, but on a more limited scale. They can still have many terminals, but not as many as themainframes. They can store a tremendous amount of information, but again usually not asmuch as the mainframe. +edium and small businesses typically use these computers.+icrocomputers are the types of computers we are using in your classes at !loyd $ollege.These computers are usually divided into desktop models and laptop models. They areterribly limited in what they can do when compared to the larger models discussed above because they can only be used by one person at a time, they are much slower than the larger computers, and they can not store nearly as much information, but they are ecellent whenused in small businesses, homes, and school classrooms. These computers are inepensiveand easy to use. They have become an indispensable part of modern life. Computer Tasks i.Inputii.Storageiii.1rocessingiv. utput3hen a computer is asked to do a 2ob, it handles the task in a very special way. &.It accepts the information from the user. This is called input.6.It stored the information until it is ready for use. The computer has memory chips, which are designed to hold information until it is needed.(.It processes the information. The computer has an electronic brain called the $entral 1rocessing -nit, which is responsible for processing all data and instructions given to the computer./.It then returns the processed information to the user. This is called output.%very computer has special parts to do each of the 2obs listed above. 3hether it is amultimillion dollar mainframe or a thousand dollar personal computer, it has the followingfour components, Input, +emory, $entral 1rocessing, and utput.  The central processing unit 9$1-: is the electronic brain of the computer. The $1- in a personal computer is usually a single chip. It organizes and carries out instructions that comefrom either the user or from the software. The processor is made up of many components, but two of them are worth mentioning at this point. These are the arithmetic and logic unitand the control unit. The control unit controls the electronic flow of information around thecomputer. The arithmetic and logic unit, A8-, is responsible for mathematical calculationsand logical comparisons.The processor is plugged into the computer*s motherboard. The motherboard is a rigidrectangular card containing the circuitry that connects the processor and all the other components that make up your personal computer. In most personal computers, some of thecomponents are attached directly to the motherboard and some are housed on their own smallcircuit boards that plug into the epansion slots built into the motherboard. Input Devices A computer would be useless without some way for you to interact with it because themachine must be able to receive your instructions and deliver the results of these instructionsto you. Input devices accept instructions and data from you the user. Some popular inputdevices are listed below.;eyboard+ouseScanner +icrophone$<=> +oystick  Memory A personal computer must have a means of storing information 9data: and instructions so thatit can perform processing tasks on the data. 1ersonal computers have two types of memory.These are discussed below.>ead nly +emory 9> +:> + is a small area of permanent memory that provides startup instructions when thecomputer is turned on. ?ou can not store any data in > +. The instructions in > + are set by the manufacturer and cannot be changed by the user. The last instruction in > + directsthe computer to load the operating system. %very computer needs an operating system. This is a special computer program that must beloaded into memory as soon as the computer is turned on. Its purpose is to translate your instructions in %nglish into #inary so that the computer can understand your instructions.The operating system also translates the results generated by your computer into %nglishwhen it is finished so that we can understand and use the results. The operating systemcomes with a computer.>andom Access +emory 9>A+:  This is the area of memory where data and program instructions are stored while thecomputer is in operation. This is temporary memory. @ T% The data stored in RAM islost forever when the power is turned off. !or this reason it is very important that you saveyour work before turning off your computer. This is why we have peripheral storage deviceslike your computer*s hard disk and floppy diskettes. 1ermanent +emory 9Auiliary Storage:?our files are stored in permanent memory only when saved to your disk in a drive or savedto your computer0s hard disk, <rive c In the !loyd $ollege labs, you can also save your work to a network drive. 3e will discuss this in class.To better understand how a computer handles information and to also understand whyinformation is lost if the power goes off, let*s take a closer look at how a computer handlesinformation. ?our computer is made of millions of tiny electric circuits. !or every circuit ina computer chip, there are two possibilities&.an electric circuit flows through the circuit or 6.An electric circuit does not flow through the circuit.3hen an electric current flows through a circuit, the circuit is on. 3hen no electricity flows, the circuit is off. An BonC circuit is represented by the number one 9&: and an off circuit is represented by the number zero 9):. The two numbers & and ) are called bits. The word bit comes from Bbinary digitC. %ach time a computer reads an instruction, it translates that instruction into a series of bits, &*s and )*s. n most computers every character from the keyboard is translated into eight bits, a combination of eight &*s and )*s. %ach group of eight  bits is called a byte. #yte D The amount of space in memory or on a disk needed to store one character. E bits F & #yteSince computers can handle such large numbers of characters at one time, metric prefies are combined with the word byte to give some common multiples you will encounter in computer literature. ;ilo means &))) ;ilobyte 9;#: F&))) #ytes+ega means &,))),))) +egabyte 9+#: F &,))),))) #ytesGiga +eans &,))),))),))) Gigabyte 9G#: F&,))),))),))) #ytes At this point it would be good to point out why information stored in >A+ is lost if the power goes off. $onsider the way the following characters are translated into binary code for use by the computer.A)&)))))&#)&))))&)$)&))))&&H)&)&&))))&)&&)&)&))&&)))&6))&&))&)$onsider the column at the right, which represents how the computer stores information. %ach of the &*s in the second column represents a circuit that is BonC. If the power goes off, these circuits can @ T be BonC any more

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