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Introduction to Computers

By Rave Harpaz

Computer Science Dept.

Brooklyn College

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What Is A Computer?

A computer is an electronic device, operatingunder the control of instructions (software)stored in its own memory unit, that canaccept data (input), manipulate data(process), and produce information (output)from the processing. Generally, the term isused to describe a collection of devices thatfunction together as a system.

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Devices that comprise a computer system

Printer (output)

Monitor (output)

Speaker (output)

Scanner (input)

Mouse (input)

Keyboard (input)

System unit

(processor, memory…)

Storage devices

(CD-RW, Floppy, Hard disk, zip,…)

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What Does A Computer Do?

Computers can perform four generaloperations, which comprise the informationprocessing cycle.

Input

Process

Output

Storage

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Data and Information

All computer processing requires data, which is a collection ofraw facts, figures and symbols, such as numbers, words,images, video and sound, given to the computer during theinput phase.

Computers manipulate data to create information. Informationis data that is organized, meaningful, and useful.

During the output Phase, the information that has been createdis put into some form, such as a printed report.

The information can also be put in computer storage for futureuse.

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Why Is A Computer So Powerful?

The ability to perform the information processing cycle with amazing speed.

Reliability (low failure rate).

Accuracy.

Ability to store huge amounts of data and information.

Ability to communicate with other computers.

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How Does a Computer Know what to do?

It must be given a detailed list of instructions, called a compute program or software, that tells it exactly what to do.

Before processing a specific job, the computer program corresponding to that job must be stored in memory.

Once the program is stored in memory the compute can start the operation by executing the program instructions one after the other.

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What Are The Primary Components Of A Computer ?

Input devices.

Central Processing Unit (containing the control unit and the arithmetic/logic unit).

Memory.

Output devices.

Storage devices.

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Input Devices

Keyboard.

Mouse.

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The Keyboard

The most commonly used input device is thekeyboard on which data is entered bymanually keying in or typing certain keys. Akeyboard typically has 101 or 105 keys.

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The Mouse

Is a pointing device which is used to controlthe movement of a mouse pointer on thescreen to make selections from the screen. Amouse has one to five buttons. The bottom ofthe mouse is flat and contains a mechanismthat detects movement of the mouse.

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The Central processing Unit

The central processing unit (CPU) containselectronic circuits that cause processing tooccur. The CPU interprets instructions to thecomputer, performs the logical and arithmeticprocessing operations, and causes the inputand output operations to occur. It isconsidered the “brain” of the computer.

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Memory

Memory also called Random Access Memoryor RAM (temporary memory) is the mainmemory of the computer. It consists ofelectronic components that store dataincluding numbers, letters of the alphabet,graphics and sound. Any information stored inRAM is lost when the computer is turned off.

Read Only Memory or ROM is memory that isetched on a chip that has start-up directionsfor your computer. It is permanent memory.

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Amount Of RAM In Computers

The amount of memory in computers istypically measured in kilobytes or megabytes.One kilobyte (K or KB) equals approximately1,000 memory locations and one megabyte(M or MB) equals approximately one millionlocations A memory location, or byte, usuallystores one character.

Therefore, a computer with 8 MB of memorycan store approximately 8 million characters.One megabyte can hold approximately 500pages of text information.

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Output Devices

Output devices make the informationresulting from the processing available foruse. The two output devices more commonlyused are the printer and the computerscreen.

The printer produces a hard copy of youroutput, and the computer screen produces asoft copy of your output.

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Storage Devices

Auxiliary storage devices are used to storedata when they are not being used inmemory. The most common types of auxiliarystorage used on personal computers arefloppy disks, hard disks and CD-ROM drives.

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Floppy Disks

A floppy disk is a portable, inexpensivestorage medium that consists of a thin,circular, flexible plastic disk with a magneticcoating enclosed in a square-shaped plasticshell.

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Structure Of Floppy Disks

Initially Floppy disks were 8-inches wide, they thenshrank to 5.25 inches, and today the most widelyused folly disks are 3.5 inches wide and can typicallystore 1.44 megabytes of data.

A folly disk is a magnetic disk, which means that itused magnetic patterns to store data.

Data in floppy disks can be read from and written to.

Formatting is the process of preparing a disk forreading and writing.

A track is a narrow recording band that forms a fullcircle on the surface of the disk.

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The disk’s storage locations are divided into pie-

shaped sections called sectors.

A sectors is capable of holding 512 bytes of data.

A typical floppy stores data on both sides and has 80tracks on each side with 18 sectors per track.

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Hard Disks

Another form of auxiliary storage is a hard disk. Ahard disk consists of one or more rigid metal platescoated with a metal oxide material that allows datato be magnetically recorded on the surface of theplatters.

The hard disk platters spin at a high rate of speed,typically 5400 to 7200 revolutions per minute (RPM).

Storage capacites of hard disks for personalcomputers range from 10 GB to 120 GB (one billionbytes are called a gigabyte).

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Compact Discs

A compact disk (CD), also called an optical disc, is aflat round, portable storage medium that is usually4.75 inch in diameter.

A CD-ROM (read only memory), is a compact discthat used the same laser technology as audio CDs forrecording music. In addition it can contain othertypes of data such as text, graphics, and video.

The capacity of a CD-ROM is 650 MB of data.

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Computer Software

Computer software is the key toproductive use of computers.Software can be categorized intotwo types:

Operating system software

Application software.

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Operating System Software

Operating system software tells the computerhow to perform the functions of loading,storing and executing an application and howto transfer data.

Today, many computers use an operatingsystem that has a graphical user interface(GUI) that provides visual clues such as iconsymbols to help the user. Microsoft Windows98 is a widely used graphical operatingsystem. DOS (Disk Operating System) is anolder but still widely used operating systemthat is text-based.

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Application Software

Application Software consists of programsthat tell a computer how to produceinformation. Some of the more commonlyused packages are:

Word processing

Electronic spreadsheet

Database

Presentation graphics

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Word Processing

Word Processing software is used to create and printdocuments. A key advantage of word processingsoftware is that users easily can make changes indocuments.

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Electronic Spreadsheets

Electronic spreadsheet software allows the user toadd, subtract, and perform user-defined calculationson rows and columns of numbers. These numberscan be changed and the spreadsheet quicklyrecalculates the new results.

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Database Software

Allows the user to enter, retrieve, and update data inan organized and efficient manner, with flexibleinquiry and reporting capabilities.

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Presentation Graphics

Presentation graphic software allows the user tocreate documents called slides to be used in makingthe presentations. Using special projection devices,the slides display as they appear on the computerscreen.