Modem

A Modem (short for modulator-demodulator) is a computer peripheral that allows your computer to connect to, and communicate with, other computer via telephone lines. This device converts the digital signal produced by the computer into analogue signals. These analogue signals are sent along a telephone lines to another modem, where they can are converted back into digital signal for the receiving computer. Anything that can be stored on a computer can be sent to another computer when connected by a modem and a phone line.

There are two types of modems available, namely: Internal and external modems.

Internal modem: An internal modem is fixed into an expansion slot located on the computer main board or it may be part of the computer main board (then known as integrated modem).

External modem: It is a separate unit, and connects to the computer via a cable. Five or six small lights on the top, or in front of the modem case, indicates the status of the modem and that of the data it is sending or receiving.

Advantage and Disadvantage of Networking.

Advantages:

1. Expensive peripherals devices such as laser printers and scanners can be shared between users.

2. Messages can be sent between users using LANs or WANs.

3. All users can access the same files.

4. It is possible to access data or programs from any terminal/workstation.

5. Data and software can be stored centrally, which makes them easier to maintain and back up.

Disadvantages:

1. If a WAN is used, sophisticated (complicated) equipment is needed and the rental of telecommunication links makes it very expensive.

2. File security is more important with networks. For instance, if a virus were to get onto network then it could effect all the network terminals.

3. Wiring can be expensive both to buy and to install.

4. In a type of network called a file-server network all the programs and data is stored on a main computer called a server. If the server breaks down, the whole network become unusable.

5. Networks are unpredictable; they need an experienced person to keep them running successfully.

Hierarchical networks

Hierarchical networks are those networks where one or more computers are more powerful than the rest. Hierarchical networks are often called client-server networks because a more powerful computer called the server is used to look after printing, file maintenance and other peripherals. There are two types of server: the print server and the file server.

The file server is a computer used for managing the files on a network. It is used to store both programs and data and is generally more powerful computer than the others to which it is connected. A print server is the name given to a computer in a network which has a printer connected. This server manages all the print requests from users on the network.

Star Topology

In the star topology, there is a computer at the centre that is used to control the whole of the network. If centre machine break down, then the whole network breaks down. Star topologies use more cabling and therefore more expensive than other topologies. There is a path from each terminal to the central computer; this type of topology is very fast.

Line or (Bus) Topology

In line or bus network, the data is sent to all the device on the network at the same time. This means that if a terminal is not working properly others are not affected. Like in ring topology, there is no central computer used to control the network so each of the terminals has equal status. The main advantage of the line or bus network is that it is cheap and reliable.

Ring Topology

In the ring topology the terminals or other equipments are connected together in a circle. One of the main disadvantages in the ring topology is that if there is a break in any part of the communications line, then all of the device on the network will be affected.

NETWORKS

A network is a series of computer systems that are linked together so that they are able to share computing power or storage facilities. The link may be between computers in the same building or between computers in different parts of the country or even in different parts of the world.

Local Area Networks are confined to a small area. In LAN the connections are made using cables. A LAN allows the users to share programs and resources such as printers and backing store. It allows users to send message to each other using a local electronic mail system. This can be very convenient if people are not always in the same place as they can read their message at any convenient network terminal.

The way in which a network is laid out is called the network topology

PROGRAMMING LANGUAGES

A program is a set of instruction that the computer can understand. The computer can understand only binary code, all computer languages must be eventually reduced to binary code and the way this is done depends on the type of language used.

Low-Level-languages

Low-level languages are languages that are easy for the computer to understand but more difficult for the programmer to understand. Assembly language and Machine language (Machine code) collectively called low-level language.

Machine Language (or Machine code)

Machine language is the language directly understood by the machine. It consists of a series of 1’s and 0’s. Machine code is often machine specific, which means that one computer’s machine code will not be understood by a different type of computer. A program written in machine code needs no translation and is therefore very fast.

Assembly Language

An assembly language is a language that uses simple instruction such as ADD, SUB and is used in preference to machine code, since it is easier for the programmer to use and to debug (debugging means removing any mistake from the program). Once a program has been written in assembly language it needs translating into machine code by software called as assembler before it can be understood by a computer.

High-Level Language

High-level language is developed with the programmer in mind rather than the computer. Such language have the advantage that they are not as machine-dependent as machine codes or assembly language, so once a program has been written it can be used on different computers with very little alteration.

It is similar to English, which means that programming is made easier.

Advantages of high-level language

: Simple instructions similar to English make high-level language easy to understand

: It is easy to correct errors and test program.

: Program written in high-level languages can be used on different makes of computer.

Examples for high-level language

COBOL, BASIC, FORTON, C++, LOGO, JAVA, HTML (Hypertext Markup Language)

Compiler and Interpreters

Compiler & Interpreter are both programs that change high-level language instruction into machine-code. An interpreter is a translator of high level language program. These translators translate one instruction at a time.

A Compiler is a translator which is used to translate the whole source of a program at a time.

TAILOR-MADE SOFTWARE

Although specialist software might be the answer for many companies, there will be some organizations who find that it just doesn’t do exactly what they want or it doesn’t work with their current systems.

In this case, they might decide to have the software system they need designed and developed specially for them. This is called ‘tailor-made’ or ‘bespoke’ software.

The main advantages are:

§ The company will get the exact software / system that they need

§ The software will work exactly how they want it to work.

§ The software will only have the features that they specifically need in their business.

The main disadvantages of this approach are:

§ It takes a long time to develop such a system, between a few months to years.

§ It costs a great deal of money to develop such a system.

§ The company may need to employ a team of people such as business analysts, programmers, testers etc.

§ There will be little in the way of user support and online help.

GENERAL PURPOSE SOFTWARE

A general purpose application, sometimes known as ‘off-the-shelf’ is the short of software that we use at home and school. Examples include word processor, spreadsheet, desktop packages, graphics packages etc.

It provides many features that the majority of users will want Eg; formatting text, creating charts, organizing tables etc. There will be a vast number of features that we many never use Eg; statistical functions, mail merge etc. This will make the storage size of these applications fairly large.

There are several good reasons for using general purpose software:

Ø It is relatively cheap

Ø It is easily available from most computer shops

Ø It will have been thoroughly tested so there won’t be any serious problem or bugs.

Ø There will be lots of user support i.e. books, user guides, online help and discussion forums on the internet.

SPECIALIST SOFTWARE

Specialist application packages are generally not available in shops and they often have to be purchased directly from the manufacturer or a specialist firm. These application are designed to be used for specific tasks such as company payroll, stock control systems, e-commerce sites etc.

The application has not been written for a specific company. They have been developed by a manufacture to try to provide all of the features that they anticipate a company might need.

Like general purpose software, there may be many features that the company does not need, or the feature which is available may not work exactly as they would like in their business

APPLICATION SOFTWARE

Application software is used to perform specific tasks. A software application carries out tasks that the user is interested in doing such as writing a letter, creating graphs, sending an email or downloading a webpage.

Application software can be classified under three main categories:

Ø General purpose software.

Ø Specialist software.

Ø Tailor made software.

Integrated packages

Some manufactures decided to put a selection of the most popular general purpose software together and sell it as one package at a much cheaper price than buying each package individually. This is called an integrated package.

An example of an integrated package is ‘Microsoft Office’ which contains Word, Excel, Access, and PowerPoint.

UTILITY PROGRAMS

Utility programs are part of the system software. They are designed to do one or two specific but vital tasks very well.

Some utility programs might be supplied as part of the operating system, others are purchased separately.

Some common tasks carried out by utility programs are:

Ø Renaming files.

Ø Deleting files.

Ø Sorting data.

Ø Repairing damaged files.

Ø Sending files to printer.

Ø Copying files.

Batch processing

It is often not desirable to deal with the inputs until a certain number have occurred or a set time has passed. So they are stored until the system comes online to process the data in one 'batch'. Batch processing is usually fully automatic unlike 'real-time' or transaction processing which are interactive.

For example

• A stock control programme may store records of every item sold in a shop that day. Then, at the end of each day it calculates what needs to be ordered.
• An online competition stores all the entries until it is time to find the winner.
• Electricity, gas and telephone bills are usually calculated on a monthly basis.

Real time processing

Real time processing is usually found in systems which use computer control. Real time processing has to be programmed very carefully to ensure that no input events are missed. For example, a traffic light system is a real-time system but it only needs to process data relatively slowly. On the other hand, controlling a car engine has to deal with input events happening every thousandth of a second so a very fast computer is needed to do this -but both the traffic-light and the car engine computers are carrying out 'real-time' processing.

Examples:

• Traffic lights
• Heart rate monitoring
• Aircraft control
• Computer games

OPERATING SYSTEM

The software and the hardware can't work together without something to act as an 'in-between'. The task of co-ordinating all of the software and hardware is given to the Operating System.

What is an operating system?

There are two main categories of software. There is 'application software' with examples such as word processors, spreadsheets and databases. The other main category is called 'system software' which includes the operating system and utility programs.

The operating system is needed to control everything happening in your computer. It controls the memory, the disks, the peripherals and the application software.

Tasks of the operating system:

Sorting out where to store data on disk drives.

Dealing with security – user name and passwords

Organizing files and folders.

Managing data transfer from the CPU to the peripherals eg: printer, monitor, etc

Deals with saving, deleting, opening, closing files.

Example for operating system:

Mac OS, LINUX, WINDOWS XP, WINDOWS 2000, WINDOWS NT, UNIX

Single user operating system

The operating system on your computer only has to deal with the tasks you are giving it. It doesn't need to worry about sharing out memory, hardware or processing time. This is called a single user operating system. Examples of such operating systems are Microsoft Windows 95, 98, 2000, XP and Vista as well as the Mac OS range.

Multi user operating system

“Multiuser software allows several users to access the same data at the same time. A multiuser operating system needs to be used with most networks.”

Multi tasking operating system

Multitasking means the ability of a computer to run two more programs at the same time.

Digital Versatile Disk (DVD)

DVD is similar to a CD in that it is an optical device and that a laser is used to store the data and read the data. A single sided DVD can store about 4.7 GB of data. DVDs which store data on both sides can hold over 9 GB of data. One problem with the DVD is that the different companies which make them haven't agreed on a standard format. Because of this, you will see various kinds of DVD disks for sale: DVD-R, DVD+R, DVD-RW and DVD+RW.

Advantages

• Very large storage capacity
• Sound and picture quality is excellent, making them ideal for storing films with video and sound.
• DVDs are now mass produced so they are relatively cheap
• DVD players can read CDs

Disadvantages

• DVDs do not work in CD drives
• There is no single standard of DVD
• They can be easily damaged by breaking or scratching

OUTPUT DEVICES

1.     Monitors:

A monitor (or screen) is the most commonly used output device. They come in many different shapes, sizes and forms. Size of the screen actually indicates the length of the diagonal, so a 17 inch screen has a 17 inch diagonal. The picture on a monitor is made up of thousands of tiny coloured dots called pixels. The quality and detail of the picture depends on the number of pixels that the monitor can display. The higher the number of pixels, the better quality the output.

The two types of monitor that you need to know about are Cathode Ray Tube monitors (CRT) and Thin Film Transistor monitors (TFTs)

Cathode Ray Tube monitors (CRT)

CRT monitor are large and bulky and have a glass screen which makes them fairly robust and difficult to damage. They produce quite a lot of heat so when you have an office with lots of them it could get quite warm. They are also fairly noisy compared to newer TFT monitors.

Thin Film Transistor monitors (TFTs)

TFT monitors used to be very expensive but now the price has come down they are beginning to replace all of the old CRT monitors. Not only do they look much nicer they take up a lot less space. They are quieter than CRT monitors and also create less heat.

They are easier to damage than CRT screens. A few sharp pokes at the screen with a pencil can cause lasting damage. Another disadvantage is that unless you have a very high quality TFT monitor, the colours and contrast are not so good as a CRT monitor and so the picture can look a bit dull.

2.     Printers:

Printers are another common output device. They are used to create a 'hard' copy of your work i.e. something that you can hold, hand to someone else or file away.

Laser printers:

Laser printers are used in many workplaces because they are quiet, they print a large number of sheets very quickly and they produce high quality documents.

They print in the same way as photocopiers. Powdered ink, called 'Toner', is fused onto paper by heat and pressure.

Advantages

• High quality printouts - better than ink-jet or dot-matrix
• Fast printouts - faster than ink-jet or dot-matrix
• Prints very quietly - quieter than ink-jet or dot-matrix
• Cost per page is low - cheaper than ink-jet or dot-matrix

Disadvantages

• Most expensive printer type to buy, especially colour lasers
• Toner is more expensive than ink-jet cartridges
• Expensive to repair - lots of complex equipment inside
• Fairly bulky - larger than ink-jet printers

Inkjet printers:
They are relatively cheap to buy and most of them can combine both black and white and colour printing at the same time.

These printers use cartridges which contain ink. They operate by heating the ink as it flows through the nozzle. The heating process causes a small droplet of ink to form. This is then released as a single dot which forms part of a letter or image. This is why the printouts often come out of an ink-jet printer still slightly wet.

Colour ink-jet printers are ideal for use at home where only a few documents need to be printed and the quality of the printout doesn't need to be perfect.

Advantages

• Cheap to buy - cheaper than a laser printer
• More compact than a laser printer
• Cartridges cost less to replace than toners
• Produce good quality printouts better than a dot-matrix but not as good as a laser
• Speed - faster than a dot-matrix but not as fast as a laser

Disadvantages

• Noisier than a laser printer (but not as noisy as a dot-matrix)
• Colour printing can be extremely slow
• Cost of printouts per page are more expensive than a laser printer
• Cartridges need to be replaced more often than a laser printer
• Ink will smudge while it is still wet
• Colours can become saturated and often don't look the same as on the screen
• If not used for a while, the cartridges can dry out

Dot matrix printers:

These were the first type of printers to be used in homes and schools but they are not used much nowadays.

They are also called 'impact printers'. The print head contains a grid of pins and different combinations of pins are pushed out to form different characters. The print head then hits a carbon ribbon leaving an imprint on the paper. This makes them fairly noisy as you can hear the pins striking the paper.

They are also useful when continuous paper needs to be used for example printing large quantities of invoices or bills. They can be printed onto paper with perforations and then separated by tearing once the printing is complete.

Advantages

• Relatively cheap to buy
• Low operating costs
• Can print on continuous stationary
• Create carbon copies using carbonated paper

Disadvantages

• Print quality is poor and important documents are not suitable to give to managers or customers
• Very slow - slowest out of all three printers
• Noisy - you wouldn't want one of these printing all day in the office
• Cannot produce colour copies

 

3.     Plotter:

Plotters are a specialist type of printer which is able to draw high quality images on very large pieces of paper, for example 3 foot wide by 10 foot long.

They are used by engineers, architects and map-makers to draw plans of buildings, diagrams of machines or large scale maps.

A plotter differs from a printer in that it draws images using a pen that can be lowered, raised and moved across the paper to form continuous lines. The electronically controlled pen is moved around the paper by computer controlled motors.
There are three different types of plotter:
Flatbed plotters - These hold the paper still while the pens move
Drum plotters - These roll the paper over a cylinder.
Pinch-roller plotters - These are a mixture of the two types above

Advantages

·         Drawings are of the same quality as if an expert drew them

·         Larger sizes of paper can be used than most printers can manage

Disadvantages

• Plotters are slower than printers because each line is drawn separately
• They are often more expensive than printers
• They do not produce very high quality text printouts

4.     Speakers:

Most computers are fitted with a small internal speaker which can produce beeping sounds to alert you if you make an error. Computers can also be fitted with a sound card (or chip) which will enable sound to be output through external speakers. These usually produce a much higher quality sound than the internal speaker.

Advantages

• Everyone in the room can hear the output from the computer.
• They can help create an atmosphere or ambiance to accompany a presentation
• They help blind people to use the computer because text can be converted into sound

Disadvantages

• The output from speakers can disturb others who are trying to work
• High quality external speakers can be expensive

USER INTERFACE

The user interface is what we see when we turn on the computer; it consists of the cursors, icons, menus, etc.

User interface may be:

: Command Driven Interface (CDI)

: Menu Driven Interface (MDI)

: Graphical User Interface (GUI)

Command driven interface: An interface through which the user types commands for the computer to carry out tasks Eg: MS-DOS

Advantage:

1.      If the user knows the correct commands then this type of interface can be much faster than any other type of interface.

2.       This type of interface needs much less memory (RAM) in order to use it than other user interfaces.

3.      This type of interface does not use as much CPU processing time as the others do.

4.       A low resolution, cheaper monitor can be used with this type of user interface.

 

Disadvantage:

1.      For someone who has never used a command line interface it can be very confusing.

2.      Commands have to be typed in precisely, if there is a spelling error the command will fail.

3.       If you mis-type an instruction, it is often necessary to start all over again.

4.      There are a large number of commands which need to be learned

Menu driven interface:  This type of interface produce a list of commands or options available within a program and the user can make a selection by using either a mouse or keyboard.
They are extremely easy to use, someone who has never seen the interface before can workout what to do.

 

Advantages:

1.      There are no commands to learn or remember.

2.      Step-by-step options are given so that the user doesn't have to remember anything.

3.       Even if you don't know what to do, you can usually guess you way around the options.

Disadvantages:

1.       A poorly designed menu interface may be slow to use

2.      It can be irritating if there are too many menu screens to work through - users get annoyed or bored if it takes too long.

3.      You often can't go to the exact place you want right at the start. You have to work your way through the menu screens even if you know where you want to get to.

4.      The menu can take up a large part of the screen so you have to keep flicking back and forwards between applications

 

Graphical user interface: An interface that allows a user to communicate with the computer through pictures (icons), Menus, windows etc.

Advantage:

1.      This type of user interface is extremely easy to use, especially for a beginner

2.      It is easy to explore and find your way around the system using a GUI

3.      You do not have to learn complicated commands

4.       There are usually good help facilities provided with GUIs

5.      They let you exchange data between different software applications

 

Disadvantage:

1.      GUI take up a much larger amount of hard disk space than other interfaces

2.      GUI need significantly more memory (RAM) to run than other interface types

3.      GUI use more processing power than other types of interface