UNIT 2 Computer Architecture 15

Computer Users

INTRODUCTION

A computeris a device that processes dataaccording to a set of instructions known as a program.The equipment is known as the hardwareand the programs and data are the software.A special set of programs, called an operating system,provides an interface for the user and allows applications programs to communicate with the hardware. Common applications programsinclude wordprocessorsfor creating and editing texts, spreadsheetsfor calculating mathematical formulae and databasesfor storing data in a way that allows the data to be sorted and searched. Anti-virus programsare used to detect and remove viruses(harmful programs that can reproduce themselves and attach themselves to other programs). Some operating systems have graphical (user) interfacesthat allow the computer user to select items from menus(lists of choices) and to start programs using an input device called a mouse.This is done by pressing a button on the mouse i.e. clickingthe mouse. The main device for inputting the data is a typewriter-style keyboardand the output is commonly displayed on a monitorscreen that looks like a small television screen.

There is a range of sizes and types of computer. Those designed for use by one person at a time are known as personal computers (PCs)although the term PC is usually only applied to personal computers that are compatible with the standards laid down by the company known as IBM(International Business Machines). Personal computers include desktopcomputers (for use on an office desk) and handheldcomputers that can be carried around by the user. Electronics can be added to desktop computers by plugging in expansion cards(electronic circuit boards that can be plugged into special sockets called expansion slots).

It is also possible to build all the main parts of a computer into one electronic integrated circuit packaged as a single electronic chip(the common name for a microchip; an electronic integrated circuit in a small package) i.e. the 'computer on a chip'.This enables computers to be built into other devices including household devices such as washing machines and fridges and to be incorporated into plastic cards i.e. smart cards,which are able to store information such as health records, drivers' licences, bank balances, etc. Devices that include a computer circuit are commonly referred to as smart devices. A multimedia computercan process different forms of data including text, graphics, audio(sound), animation and video. This enables computer systems to be used for a combination of education and entertainment, sometimes referred to as edutainment.

Unlike most machines, computers do not have a fixed purpose. They are multi-purpose tools. They can be used in a very wide variety of situations and are found in a wide range of systems including security systems, cars and phones. Advanced systems, known as expert systems,enable computers to 'think' like experts. Medical expert systems, for example, can help doctors diagnose an illness and decide on the best treatment. As computer systems are developed, they are becoming more common and are gradually being used for more and more purposes. How they are developed, and for what purposes they are actually used in the future, can be influenced by computer users. A variety of devices known as peripheralscan be added externally to a computer. One of the most common peripherals is a printerused for printing the computer output(the processed data or signals that come out of a computer system)

UNIT1 Computer Users

on paper. A digital cameraallows photographs to be input to a computer for editing.

Not all computer systems are compatiblei.e. they cannot use the same programs and data. Connecting computers together to form a networkcan provide the 'connectivity'required to enable computers and software to communicate and to share resources. Networks connected together form an internet.The connection of networks throughout the world is known as the Internet(note that a capital I is used) or, more simply, the Net.Various communication services are available on the Internet, including email(electronic mail) for sending and receiving text messages and IRC(Internet Relay Chat) which allows users to communicate using text messages in real-timei.e. without any delay, while the users are logged on(connected to a network system account, normally using a password) to the system. An Internet service called FTP(File Transfer Protocol) is used for transferring data or program files between the powerful servercomputers that provide the network services and the clientcomputers that use these services e.g. downloading music files. Note that copying data from a larger server system to a client is referred to as downloadingand copying from the client to the server is known as uploading.

One of the newest and most popular services available on the Internet is the World Wide Web (WWW)which is often simply referred to as the Web(note the use of the capital W). The Web contains interlinked documents called webpages.A set of related webpages stored together on a server computer is called a website.Websites, such as Dogpile and Askjeeves, give the user

access to special programs called search | enginesthat are designed to allow the user to find relevant webpages on the Web. An Internet system designed to provide free, interactive access to vast resources for people all over the world is sometimes referred to as an information superhighway.

Services such as these allow people to telecommute(use their computers to stay in touch with the office while they are working at home). Computer uses mentioned in this unit include producing greetings cards; learning, using three-dimensional graphics programs called 'Splat the Cat' and 'Pets 3'; using the Microsoft Word wordprocessing program including features such as clipart(ready-drawn graphic images that can be inserted into documents); communicating on the Internet using email and chat programs including the use of email attachments(other types of files e.g. video files attached to simple email text messages); distance learning and videoconferencing(a form of communication over a network that uses video cameras so that the people taking part can see and hear each other); electronic classrooms or boardrooms; browsingthe Web (moving from webpage to webpage using a Web browser program); selling, using a website; painting; scanning pictures; downloading music and creating CD-ROMs(compact disk read only memory, commonly referred to as CDs).CD-ROMs are storage devices that use laser light for reading and writing data. The most common storage device is a hard disk(a set of aluminium disks coated in a magnetic material and enclosed in a vacuum-sealed case) used for storing the operating system and applications programs as well as the user's data.

UNIT 2

Computer Architecture

INTRODUCTION

There are different types of computer of

varying size and power, including the

following:

Supercomputer(the most powerful type of

mainframe)

Mainframe(large, very powerful, multi-useri.e. can be used by many people at the same time, multi-taskingi.e. can run many programs and process different sets of data at the same time)

Minicomputer(smaller than a mainframe, powerful, multi-user, multi-tasking)

Personal computer (PC)(single user)

Desktop computer(suitable size for sitting on an office desk) Workstation(most powerful type of desktop, used for graphic design, etc.) Portable(can be carried around, can operate with batteries) Laptop(large portable, can be rested on user's lap)

Notebook(size of a sheet of notebook paper)

Handheld(can be held in one hand) Pen-based(main input device is an electronic pen)

PDA(personal digital assistant, has functions such as task lists, diary, address book)

Note that the term PCusually refers to an IBM compatible personal computer i.e. an Apple Mac personal computer is not referred to as a PC. A computer that provides a service on a network e.g. storing files, sharing a printer, is known as a servercomputer. Server computers usually have a UPS(uninterruptible power supply) attached to them. This is a battery that automatically provides an electricity supply to allow the server to shut itself down properly if the main supply fails.

The processore.g. Pentium, is the most important part of the computer. It processes the data and controls the computer. Powerful computers used as servers often have more than one processor. There are two main types of memory:

a RAM(random access memory) holds the

program instructions and the data that is

being used by the processor. b ROM(read only memory) holds the

program instructions and settings required

to start up the computer.

The combination of the processor and memory is sometimes referred to as the CPU(central processing unit), although sometimes the processor itself is referred to as the CPU. The other parts connected to the CPU are known as peripherals.These can include input devices, output devices, storage devices and communications devices. Input devicesinclude: keyboards, scanners, barcode readers, digital cameras, microphones and video cameras e.g. webcams (small digital video cameras used on the Web). Output devicesinclude: monitors(VDU display screens), printers, plotters, loudspeakers, headphones. Storage devicesinclude: magnetic tape, floppy disks(diskettes), hard disks, CD-ROMs, CD-R disks, CD-RW disks, DVDs and MO disks. A common communications deviceis a modem(a modulator/demodulator used for converting digital signals to analogue signals and vice versa to allow a computer to be connected to the ordinary telephone system).

A set of connectors used for carrying signals between the different parts of a computer is known as a bus.Data is transferred constantly between the processor and memory along the system bus.Each part of memory has its own memory addressand

UNIT 2 Computer Architecture 15

the processor determines where processed data is stored by sending an address signal along an address busand data along a data bus.This is synchronised by an electronic clock in the CPU that determines the operating speed of the processor. Transferring data between the processor and RAM can slow up the computer; therefore, some very expensive, extremely fast memory is usually used as a cacheto hold the most frequently used data.

In a desktop computer, the CPU(central processing unit) and storage devices(pieces of equipment used for reading from and writing to a storage medium) are normal built inside a systemunit which consists of a metal chassis enclosed in a flat desktop or a tower shaped case. Other peripherals are attached to the system unit by cables. Each peripheral uses its own driver cardor controller(an expansion card that is plugged into special expansionslots in the system unit). Expansion cardscontain the electronics required to communicate with and control the I device e.g. videoor graphics cardsare used for monitors, soundcardsare used for audio input/output and NICs(network interface cards) are used for connecting to other computers in a network(computing devices connected together). Extra memory can also be added to the computer using special memory expansion slotsinside the computer. A portable computer that does not have enough space inside to fit expansion cards may use an external device called a port replicatorto provide connections for peripherals.

Storage devicesin the form of a diskor tapeare used to store the programs and data that are not being used. Note that the American spelling of disk is commonly used, although the British spelling, disc, is sometimes used. Before a program or data can be used, it must be transferred from the

storage device to the main RAM memory. Hard disksconsist of a set of magnetic coated metal disks that are vacuum-sealed inside a case to keep out the dust. The magnetic surfaces of the disks are formattedusing a read/write headto provide magnetic storage areas. These storage areas form concentric circles called tracksand each track is subdivided into sections called sectors.The disks are rotated at high speed and read from or written to by the read/write head that moves across the surface of the disks. In server computers, hard disks can be connected together and made to operate as one unit using RAID(a redundant array of inexpensive disks - see Unit 17). This can speed up the system and provide a way of recovering data if the system crashes(fails suddenly and completely, usually referring to the failure of a hard disk). There is a variety of optical storage devices that use laser light to read or write to a disk, including: CD-ROMs(compact disk read only memory), CD-R(recordable compact disk), CD-RW(re­writable compact disk), DVD(digital versatile disk- previously known as digital video disk).

An input devicecalled a barcode readeris a special type of scannerfor reading barcodes(a set of printed bars of varying thickness that are used to identify a product e.g. used to price items in supermarkets).

When comparing computers, the powerof the computer is important. This is mainly determined by the speedand capacity(size) of each part of the computer.

Speed is measured in hertz(Hz) i.e. cycles per second.

Capacity is measured in bytes(B) where 1 byte = 8 bits(binary digits) = 1 character.

When specifying a computer the following are normally quoted: a the speed of the processor (MHz -

megahertz, GHz - gigahertz)