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Higher / Intermediate 2Computer – Systems

Mr Climie

Part 1

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Data Representation

What you will learn here is how a computer that uses an odd number system called binary can still store all kinds of data such as numbers, text, sound or graphics.

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Representing Numbers

How We Change From Binary to Decimal

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Why Computers Use Binary

Even if there is a slight drop in voltage it will still be detected as a 1

There are only four rules for addition in binary compared to 100 in decimal[0+0=0 ; 0+1=1 ; 1+0=1; 1+1=10]

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Binary to Decimal

We can change from our number system, decimal, to the computer number system, binary

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Two’s Complement

Two's complement is the most popular method of working with negative binary numbers.

Do examples.

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Terms Used for Sizes

1Byte = 8 Bits1KiloByte = 1024 bytes1MegaByte = 1024 Kbytes1GigaByte = 1024 Mbytes1TeraBytes = 1024 GBytes

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Representing Real Numbers

What you will learn here is how numbers with fractions, real numbers, are stored on computers.

You need to know the terms mantissa and exponent.

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Mantissa and Exponent

A real number such as 612.987 can be rewritten as 0.612987 x 103

The 0.612987 is the mantissa The power of 10, the 3, is the

exponent

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Real Numbers

Real numbers are stored by a group of connected bytes of memory.

It sets aside a few bytes for the mantissa and a few for the exponent.

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Increase the Mantissa

If we increase the amount of storage for the mantissa we get a more accurate number stored, but we get a smaller range of numbers.

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Increase the Exponent

If we increase the amount of storage for the exponent, we increase the range of numbers, but we decrease the accuracy.

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Representing Text

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Text Representation

In this section, you will find out how text is stored on computers and how we can guarantee that what you type is exactly what is printed out or sent to someone else.

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Coding Text

When we type text into the computer, a numeric code is used to store it as a number.

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ASCII

This was developed in the 1960’s Due to peripherals being made by

many different makers they needed a common code.

American Standard Code for Information Interchange became the common code.

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ASCII Control Codes

Control codes can be used for device control such as cursor movement, page eject, or changing colours

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Character Set This is the set of characters that can be

displayed. If a different language is being used

then a different character set may be used.

Examples could be Latin set for English Cyrillic for Russian Chinese character set.

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Problems With ASCII

It is American. There is no code for the £. There is not a code for European

languages and the characters they use.

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Unicode

This was designed to replace ASCII and have a unique numeric code for every written language.

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Advantage of Unicode

The advantage is guaranteed correct communication between Countries Peripherals

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ASCII or Unicode

ASCII files are smaller than Unicode files

Unicode has every possible character

ASCII is an 8-bit code Unicode is a 16-bit code

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Representing Graphics

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Representing Graphics

In this section you will find out how graphics are stored on computers.

There are a couple of methods in use and we discuss them.

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Graphics Representation The computer uses two methods to

store a graphic on the computer. Bit mapped

Records ever single dot or pixel used and stores the pixels directly in the computers memory.

Vector Records how the diagram is made up by

recording how we would draw the lines and shapes used in the diagram.

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Bit Mapped Graphics The screen is

drawn using dots called PIXELS.

Each pixel is connected directly to a set (map) of memory locations.

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Bit Map Graphics and Colour If we use colour, we need

more than one bit of memory to record the pixel.

This is called bmp graphics. A drawback is the very large

size of file that can be produced by some pictures.

An advantage is we can edit individual pixels.

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Bit Depth or Number of Colours

2n is the amount of colours we can display when we use n bits to store the colours.

Sometime said as n-bit depth. 8 – bit depth or 8 bit colour= 256

colours 24 – bit colour (sometimes called true

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Vector Graphics

This records ‘how’ to draw the shape by recording the ‘attributes’ of the shape.

A big advantage is it takes up very little space to record the picture.

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Example - Circle A circle is drawn

knowing the centre co-ordinates, the radius, and the colour of the circumference.

Circle1, 200,400, 15, red.

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Bit Mapped Picture Vector Graphic Picture

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Graphic File Formats

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Graphic File Formats

In this section you will find out the different ways graphic programs save their files.

No single program or format is the best, they all have different advantages, disadvantages and uses.

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Graphic File Formats

Use the Internet to research the following graphic file formats

BMP JPEG Gif Tiff

1. What it stands for2. An advantage3. A disadvantage4. A likely use of each

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BMP Bit Mapped Pictures The standard format for Windows based

computers. It is a resolution-dependent file format.

A picture drawn on a screen of 800x600 pixel will look poor on a screen 1280x768 pixel

A drawback is the large file size An advantage is being able to work at

individual pixel levelH

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JPEG JPEG is a format that uses compression. This can lose data from an image.

If you save the compressed file again and again using the compression feature, you will lose detail over time.

JPEG files have the extension .Jpeg or .jpg

A major advantage is the file size, it is usually far smaller than BMPH

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GIF

Graphic Interchange Format Its resolution is low, it is designed

for screen only use, making it unsuitable for printing purposes.

Animated GIF images are the most common method of creating a moving banner or animation for the web.H

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TIFF Tagged Image File Format TIFF is a platform-independent

format The TIFF format was specifically

designed for scanned images and use in DTP.

Uses bitmapped images There are different versions in use,

so it is not commonly used!H

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Need for Compression

Graphic files can be very large. Compression is used to make the

file size smaller. This may mean the picture loses

some quality, but it is a more manageable size.

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Memory Used By A Picture

In this section you will find out, by calculation, how much storage is required to store pictures.

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Memory Used Calculation

We can calculate how much memory a picture will take up when stored.

There are two methods employed, it depends on whether it is displayed on a Screen

Or As a photograph

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Photograph

When we scan a photo we need to know the scan resolution in dots per inch (dpi) and the number of colours or bit depth.

We can calculate the memory required to hold it as Area of photo x dpi x dpi x bit depth

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Monitor Screen

A computer screen uses resolution and bit depth only.

We need to know the screen size in pixels and the bit depth used.

Width in pixels times height in pixels times bit depth.

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Examples

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NOW WE LOOK AT SOFTWARE DEVELOPMENT

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Computer Structure

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Computer Structure

In this section you will find out some detail about the physical parts that make up a computer system.

The first part is the main central chip of the computer called the CPU.

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Simple Diagram

Processor

Main Memory

Input Output

Backing Storage

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ALU – Arithmetic Logic Unit This is the part of the CPU where

data is processed and manipulated. The processing consists of

Arithmetical operations Logical comparisons

It will also include registers to temporarily store the results of calculations.

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Arithmetic Unit Most computer

calculations involve adding so a specialist arithmetic unit is part of the CPU.

3 times 4 or 3x4 is 3 added together 4 times.

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Logic Unit

This is special circuits designed to work out comparisons such as A<B Age > 12 (Seats=‘yes’) and (number < 6)

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Control Unit This is the part of the CPU that manages

the execution of instructions. It fetches each instruction in sequence Decodes the instruction Synchronises the commands Then executes the command

This is done by sending out control signals to the other parts of the computer.

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Registers

These hold Data being processed Instructions being executed Addresses to be accessed

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Internal Busses

Higher Content Only

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Internal Busses

In this section you will find out how the various chips that make up the main section, or motherboard, of the computer can communicate between themselves.

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What is a Computer Bus?

A bus is a set of physical connections which are used by hardware components in order to communicate with one another.

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The Computer Busses

There are three Address bus Data bus Control bus

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Address Bus

This transports memory addresses which the processor wants to access in order to read or write data.

The size of the address bus will determine how many memory locations can be addressed.

The amount of memory accessible for a bus of width n is 2n

It is a unidirectional bus. H

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Data Bus

The data bus is used to transfer data either way between the memory and the CPU.

It is a bi-directional bus

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Control Bus

It sends signals to other parts of the computer to synchronise their tasks.

It also transmits response signals from the hardware.

It is a bidirectional bus.

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Example Control Lines Reset - to return a device back to its

original state. Interrupt - the processor has to stop

doing what it was doing and deal with this new more important task.

Read – to initiate the transfer of data from the memory to the processor

Write - to initiate the transfer of data from the processor to the memory.

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Fetch Execute Cycle The main task a computer does It gets an instruction that is stored

in the memory of the computer, loads it into the cpu, then does the command it is set.

This is called the fetch/execute cyle as it does this repeatedly many times per second.

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Fetch Execute Cycle

Setup address bus Enable read line Data transferred

using data bus Command decoded Command executed

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Data Storage

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Data Storage

In this section you will get more details of how a computer stores the data it is using and storing.

Also there is a common method used to speed up the access to that data.

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Data Storage

Computers make use of various styles of storage, they include: Main memory Cache Registers Backing storage

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Main Memory

There are two styles of memory in use RAM

Random access memory is a type of computer storage whose contents can be accessed in any order

ROM Read only memory is memory whose

contents can be accessed and read but cannot be easily changed

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Use of each type

RAM holds the program and data in use at this moment.

ROM will hold parts of the operating system we need when we start the computer.

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RAM

Random access memory The contents are lost when the

power is off, this means it is volatile.

It uses a system of unique memory locations to record where the data is stored.

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ROM

Read Only Memory ROM cannot be altered. Any software held in ROM is fixed

during manufacture. Typical use is to store a basic set

of operating system commands.

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What comes next is mainly higher content, Int 2 pupils can

investigate how RAM and ROM work.

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Cache Memory –1

Cache memory is a relatively small amount (normally less than 1MB) of high speed memory that resides on the CPU

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Cache Memory – 2

Cache memory is designed to supply the CPU with the most frequently requested data and instructions.

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Backing Store Usually magnetic disks,

storing data and programs.

Backing store is cheaper but RAM is faster.

Can also be re-writeable DVD’s or CD’s, called optical storage.

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Solid State Storage Device

These devices are now very common, this is due to the capacity, physical size and robustness. They can store much more than cd’s and can match DVD’s capacity of 5 Gbytes.

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Addressability

The computer assigns numbers or addresses to physical memory locations on boot-up to keep track of the information that the CPU has access to.

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Memory Maps

The O.S. Places into RAM a list of all the known, important locations.

This is known as a memory map.

Comparison of memory maps for different O.S.

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System Performance

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How Fast Is That Computer?

In this section you will find out how we can compare computers in terms of overall speed.

We use terms such as powerful and fast but how do we compare them properly.

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Clock Speed A computer's system clock resides on

the motherboard. It sends out a signal to all other

computer components in sync. Every action in the computer is timed

by these clock cycles and takes a certain number of cycles to perform.

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Clock Speed as System Performance

This is only a basic measure. We can only compare them if they

are made by the same company. Even then they must be from the

same ‘family’ of processors.

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MIPS

Millions of instructions per second. This measures how many simple

instructions can be performed by the CPU in one second.

MIPS measures CPU performance only, not the overall system performance.

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Flops

Floating point operations per second.

This is similar to Mips but it uses real numbers with fractions in the calculations.

Is still in use for modern computers.

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How Do We Compare Computer Systems?

Mips and Flops look at the processor on its own, but that does not take into account that some disc drives are much faster than others, so we need to be careful how we measure a computers speed.

For a full comparison we use application tests which test many different programs and aspects of the whole system.

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Application Based Tests

A test that serves as a standard by which computer systems may be compared.

This takes into account the complete computer system as well as software.

Also known as benchmarks.

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More Influences

There are more methods of influencing how fast a computer works. These are in the way the computer is designed.

On the next page you will learn of some of the ways this can be designed.

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Factors That Affect System Performance

Data bus width Wider the better

Use of cache memory On board the CPU is better

Rate of data transfer to and from peripherals Modern interfaces are much faster,

USB2 is 40 times faster than USB1

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Other Methods of Increasing System Speed

Increasing clock speeds New parallel processors Increasing memory, 2 or 3 Gb Backing storage capacity1 Tb

available

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Peripherals

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What Is a Peripheral?

Peripherals may be internal or external.

Examples of peripherals include printers, monitors, disk drives, scanners and so on.

You will find out how we compensate for the difference in speed of the fast computer and the slow peripheral.

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Peripheral list

  ItemMono laser

Colour laser

Inkjet printer

DVD writer Scanner

Internal disc drive

external disc drive

tft monitor

Details                  

Resolution                  

Capacity                  

Speed                  

Compatibility                  

Name                  

Cost                  

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Practical Work

The following few slides indicate the type of peripheral you are going to research.

Write down the details as you find them.

Note we want typical information NOT specific details of an actual peripheral.

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1. Typical Characteristics of

Keyboard Mouse Microphone Touchpad

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2. Typical Characteristics of

Digital camera Scanner Webcam

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3. Typical Characteristics of

Monitor LCD panel Inkjet printer Laser printer Loudspeaker

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4. Typical Characteristics of

Hard disc drive Magnetic tape drive CD-rom, CD-R, CD-RW DVD-rom, DVD-R, DVD-RW

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Choice of Peripherals A peripheral is hardware that is

added to a computer in order to expand its abilities.

You can take in to account Resolution Capacity Speed of data transfer Compatibility Cost

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Compensating for Speed Peripherals are slow in comparison to

the computer There are methods employed to

compensate for these speed differences. Buffers Spoolers

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BUFFERS An amount of RAM on

the peripheral, used for temporary storage of data that is waiting to be sent to a device, typically a printer.

Used to compensate for differences in the rate of flow of data between components of a computer system.

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Spoolers A method by which a

disc drive can store data and feed it gradually to a printer, which is operating more slowly than the computer.

More commonly used in a network.

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Interfaces

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Interfaces

Interfaces are more than just a connector, the wrong choice can slow the speed of the computer system considerably, the right choice can speed it up.

Most of the times you do not realise the interface is there, as it should be.

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Purpose of an Interface Interfaces are used

to pass data that are different in style but can be used by the equipment connected together by that interface.

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Functions of an Interface

Buffering Data format conversion Voltage conversion Protocol conversion Handling of status signals

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Buffering

This is when a section of RAM is set aside to store the data being transferred.

It waits until a complete block of data is created, then transfers the data completely in one block.

It then creates a new block of data.

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Digital to Analogue Converter

This converts digital signals into analogue signals.

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Parallel to Serial Parallel

All bytes of data sent at once in a ‘row’

One cable per bit of data being sent

Serial One bit sent at a time,

one after the other down the same cable.

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Voltage Conversion

This may transform the mains AC to DC for the computer peripherals.

It may convert the 240volts mains to the 5 volts the computer needs.

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Interface Protocol

A formal description of the rules and formats used to allow computer and peripheral to work properly together.

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Status Registers

There will be a special register on the interface that can communicate with the CPU.

The status register could hold The printer is out of paper The disc drive is not ready The internet connection can not be

made

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Wireless

This is becoming increasingly more and more common.

There are two styles Bluetooth Wi-Fi

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Wi-Fi

It can let you use a printer in another room of the house.

You can use peripherals up to quite a long distance away. (30m).

You can share a Wi-Fi link with other users or make it secure.

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Bluetooth This is also wireless but is

much less powerful. It is designed to allow

peripherals of any kind to communicate with others.

It only works over about 10 metres distance or so.

It is much slower than Wi-Fi.

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Computer types A loose description

of computer types is Embedded Palmtop Laptop Desktop Mainframe

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Embedded

These are incorporated into other devices, rather than being stand alone computers.

Examples include digital cameras, mobile phones, music players and almost any kind of industrial  or domestic control system

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Palmtop The name for pocket computers of small

size, low weight and long battery life. Its disadvantage, comparing to a PC,

are reduced functions due to smaller memory and small screen.

It is more intended for time planning, listing addresses and notes.

Being replaced by Smart Phones such as the iPhone and similar.

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Laptop

A laptop is a computer that is characterized by mobility.

Its components are similar to a desktop except miniaturized and made for low power consumption.

Now being called a portable or notebook.

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Desktop

Designed to be used by one person only.

The most commonly used style of computer.

Easily upgraded and extended..

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Mainframe

A physically large computer which has an extensive amount of memory and disk space and is able to perform several different tasks simultaneously.

It can have hundreds or even thousands of users connected to it.

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Computer Task

Can you compare the types of computer on Type of processor Speed of processor Size of main memory Backing storage Input and out put devices