MELJUN CORTES's - Computer System Lecture

8/8/2019 MELJUN CORTES's - Computer System Lecture

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What is this unit about? Languages and translators

Operating Systems Low-level machine

Hardware

Backing storage Input devices

Output devices


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01010101100001110101011010101101010101011101010010100

10101010101010101101111111101001011010101101010101011

10101001010010101010110111111110100101101010110101010

1011101010010100101010110110111111110100101101010110101010101110101001010010101011011011111111010010110101

01101010101011101010010100101010110110111111110100101

10101011010101010111010100101001010101101101111111101

00101101010110101010101110101001010010101011011011111

11101001011010101101010101011101010010100101010110110

11111111010010110101011010101010111010100101001010101

10110111111110100101101010110101010101110101001010010

10101101010101011011101011010101101010101011101010010

1001010101010101010101011011101011010101101010101011101010010100101010101010101011011101011010101101010101

01110101101111111101001011010101101010101011101010010

10010101011010010100101010101010101011011101011010101

10101010101110101001010010101101111111101001011010101

10101010101110101001010010101010101010101010101011011

Machine Code


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Languages and Translators

Computers only understand 1s and 0s

This is called machine code.

It is very hard for people to read andunderstand

Instead of trying to write machine code,we use high level languages to program.


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High-level languages

hat does a high-level language look like?

PRINT PLEASE ENTER YOUR AGE

INPUT AGE

PRINTYOU ARE

: AGE

Short Instructions like sentences

Made up of English words


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High-level languages

High-level languages are portable. They can be translated into many differentversions ofmachine code

Machine code is not portable as it only works

for a certain processorPRINT PLEASE ENTER YOUR AGEINPUT AGE

PRINT YOU ARE : AGE

Translator


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Translators

Translators take the high-levellanguage and translate it into machinecode.

They work like human translators

J'aimelinformatique

PRINT HELLO

I like Computing

0011 1110 0011

translate


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SummaryComputers only understand 1s and 0s, which we callmachine code.

Humans write programs in high level languages becausethey are like English, and can be translated into machinecode.

High level languages can be portable which means they can

be translated into different kinds of machine code.


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Operating Systems

An operating system controls all the tasksthe computer does for you

Reads in datafrom keyboardand mouse

Sends text and

graphics to thescreen

Sends data toyour printer

Loads datainto thememory from the Hard Disk

Saves your files to disk


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Examples of Operating Systems

Microsoft Windows

Apple Mac OS X

Linux

But NOT things like:

Microsoft Word

Games Internet Explorer

These are programs that run on the OperatingSystem


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Types of File

There are two different types of file:

Program files, which are files full ofinstructions that the system runs. MicrosoftWord is a program file.

Data files, which are used by programs. AMicrosoft Word document (like a letter youwrote and saved) is a data file.


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H

H

CCII

umanuman

omputeromputer

nterfacenterface


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Human Computer Interface

The Operating System provides the HCIfor the user

User uses mouse to click icons Operating System translates into

instructions

What was clicked? What should be done now (load file, save

file, load program)?


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Types of Operating System

Interactive System

Computer reacts to user requests immediatelyand processes the data

Example: Internet ticket booking (Travel,

Concert)

What would happen if the system wasnt

interactive?

1. User clicks on link to buy ticket

2. System checks immediately if there is a

ticket available

3. Ticket is booked for the user


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Types of Operating System

Real Time System Real time systems react even faster than

interactive systems

Designed to always process the right amount of

information in time This means the Real Time system is instantevery time

Used in spaceship control systems, nuclear

reactors..

Where else would Real Time Systems be

used instead of Interactive Systems?


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Summary

Operating systems control the tasks the computer does for the user. Thisincludes loading data into memory, reading data from they keyboard andmouse, saving files and sending text and graphics to the screen orprinter.

There are two types of file - program files (such as Microsoft Word) anddata files, that are used by program files (such as a letter your wrote inMicrosoft Word)

We interact with the OS through the Human Computer Interface (HCI).The OS translates the keyboard and mouse presses into instructions and

performs actions such as loading and saving files.Interactive operating systems are used when users need immediatefeedback. Real-time operating systems are used when systems alwaysneed instant results (such as a control system on a plane).


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Check your understanding

What kind of system would you use for thefollowing (choose from background,interactive and real-time):

Flight booking web site

Controlling a robot?

On a home computer?

Running a nuclear reactor


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More Checking!

What jobs does the Operating System do? Give an example of an Operating System?

What are the 2 types of file?

What does the HCI do?

When would Interactive Processing be used? When would Real-Time Processing be used?


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Filing Systems

It is very wise to organise your files!

Lots of files in the one place = hard to

organise Group them in directories


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Filing System

The Operating Systemsorts our data using

directories (oftencalled folders) andfiles.


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Low Level Machine We now know about Operating Systems, High Level

Languages, and how we access data.

Whats next?

Now we are going right inside the computer tolook at how the CPU and memory works


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The two most important parts of the inside of the computer are the CPUand memory.

The CPU (Central Processing Unit) is the brain of the computer wherethe computer works things out.

The memory is where the computer remembers things for the CPU.


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The Computers Memory

Computers use main memory and backing storage tostore data.

Main memory is the fast memory inside a computer that

stores data the CPU is currently using

Backing store is the bigger but slower memory that storesfiles and programs for the computer

Backing store comes in two types magnetic and optical.

Magnetic Hard Disk and Floppy disk

Optical CDROM and DVD


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Main memory

Inside the computer there is main memory

Main memory is made up of memory chips

There are two kinds of main memory:

RAM RandomAccess Memory

ROM Read Only Memory


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Random Access Memory

RAMis where the computer stores data that is itcurrently using. This includes:

Data from the keyboard as you type

Data from open files and programs you areusing

When you turn off your computer, all the data in

RAM will be lost.

This is why you must always save files to backingstore before turning off a computer!


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Read Only Memory

ROMis READ ONLY you cant change it It is written in the factory when the computer is made

The computer can read the data in the ROM straightaway when the computer is switched on

This is why parts of the OS are sometimes stored on

ROM It isnt wiped when the computer is switched off

A good way to remember the difference betweenRAMand ROM is to think that RAM is like anotebook and ROM is like a textbook.

With RAM you write in what you need to remember

With ROM it is already there and you dont changeit!


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How to measure memory

We said before that everything in a computer is either a 1or a 0

This is because computers use binary numbers

The size of memory is usually given in megabytes or

gigab

ytes, but what does that mean?

Bit Binary digit: a 1 or 0

Byte 8 bits, e.g. 01101100

Kilobyte 1024 bytesMegabytes 1024 Kilobytes

Gigabyte 1024 Megabytes

Terabyte 1024 Gigabytes


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Memory size

Bit Binary digit: a 1 or 0Byte 8 bits, e.g. 01101100

Kilobyte 1024 bytes

Megabytes 1024 Kilobytes

Gigabyte 1024 Megabytes

Terabyte 1024 Gigabytes

So an iPod with 60GB of storage space has:

60

x10

24 x10

24 x10

24 x 8= 515,396,075,520 bits!

(over 515 billion bits)


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The Processor

The processor is the brains of the computerA processor takes data in, processes it and then outputs

the data to screen or printer.

Input Process Output

keyboard

mouse

calculationPrint out

Display onscreen


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Remember:

Input

Process

OutputSome real world examples of IPO..Some real world examples of IPO..


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Check your understanding Give a real life example of IPO

Give a computer example of IPO

Explain why you can not store data inROM

What happens to RAM when the

computer is switched off? Why shouldthis be ok?


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B

I

N

A

R

Y


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Binary We count in decimal

We have 10 fingers, so it makes sense

that we group by 10s I.e. 1, 10, 100,1000, 10000 etc

Computers count in binary They use different columns and group

by twos I.e. 1, 2, 4, 8, 16, 32, 64, 128


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NumbersWe count to 10:

1,2,3,4,5,6,7,8,9,10

A computer would do this in binary:1,10,11,100,101,110,111,1000,1001,1010!

Binary numbers have a power of 2, and decimal

numbers (that we count with)have a power of10. Lets go back in time


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1000 100 10 1

128 64 32 16 8 4 2 1

6 5

1 1

1 1 5

1 1 1 1 1

0

0

0 0 0 0 0

0 0

For example:


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Binary Revision Questions

What is binary for:

48, 20, 128, 7 ?

What is the decimal for:

00001000, 00001000, 00011000,

00000101 ?


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Binary Revision Answers48 = 00110000

20 = 00010100

128 = 10000000

7 = 00000111

00001000 = 8

00001000 = 9

00011000 = 24

00000101 = 5


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Binary recap

65

100

255

1

29

128 64 32 16 8 4 2 1

01000001

01100100

11111111

10000001


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Storing Text and Graphics If computers can only work with binary

numbers, how do they store words and

pictures etc?


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Storing Text

Since computers only use binary, they have a

binary code for each character This code is called ASCII

American Standard Code for InformationInterchange

Binary Decimal Character

1000001 65 A

1000010 66 B

1000011 67 C

1000100 68 D

1000101 69 E1000110 70 F

Lets try some ASCII conversion.


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ASCII Table

http://www.ascii.cl/htmlcodes.htm


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ASCII TABLE65 A

66 B

67 C

68 D

69 E

70 F

71 G

72 H

73 I

74 J

75 K

76 L

77 M

78 N

79 O

80 P

81 Q82 R

83 S

84 T

85 U

86 V

87 W

88 X

89 Y

90 Z


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The size of a text file

Hello

The eagle has landed!

How many bytes would these files take up?

Text is stored in the computer using ASCII codes

Each characters ASCII code is8-bits, i.e. 1 byte in size

So, we can work out the storagerequirements of text files

5

21


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Storing graphics

A graphic can be a drawing, graph, paintingor photograph.

Graphics are made up of a grid ofpixels.

Apixel is a single point on the screen.


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Storing Graphics In black and white graphics, the grid of

pixels can be represented by binary

numbers 1 stands for a black square, 0 stands for

a clear square.

Each pixel takes up 1-bit to store.


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1 0 0 1 1 0 0 1

0 1 0 1 1 0 1 0

0 0 1 1 1 1 0 0

0 0 0 1 1 0 0 0

1 0 0 1 1 0 0 0

1 1 1 1 1 0 0 0

0 0 0 0 1 1 1 0

0 0 0 0 0 0 1 0

How many bits do you

think it will take tostore this graphic?

The grid is 8 x 8 pixels, so itwill take 64 bits to store.

64 bits is 8 bytes.


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Colour Graphics

To store colour graphics, we need to

assign each colour a different numbere.g. red = 1, blue = 2 etc.

These colour codes are stored in binary

The larger the binary number, the morecolours we can have. How many do weneed?

32-bit graphics are normal (4.3 billion

different colours)


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Systems task 9

10 minutes on Systems Task 9, page 25

If finished, go onto Knowledge Check 5


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Summary Computers store text and graphics in binary.

They use a code called ASCII (American Standard Code forInformation Interchange)

Each character has a code in ASCII Black and white graphics are stored by using 1 bit for each pixel

(1 for black, 0 for white).

We can work out the size of these graphics by multiplying thewidth of the graphic by the height.

Colour graphics use more bits for each pixel depending on howmany colours are needed.


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Hardware

Weve covered how the CPU works, and

what the Operating System softwaredoes

Now let us look at hardware for thecomputer


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Microprocessor

The chip is made of layers of silicon crystalwavers on which very small electronic

components are installed.


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Backing Storage

Backing storage memory is used to store fileswhen the computer is switched off, and areusually removable.

There are two types of backing storage,Optical and Magnetic. Well look atmagnetic first.


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Tape Drive

Tape drives take large plastic tapes which store data in binary usingmagnetic spots to encode the data

They have a large capacity, and fast data transfer rates

Tapes wear over time so need to be stored in suitable environment andare suited to medium and short term storage

DAT tapes can hold up to 200 Gigabytes so are used for backup


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Floppy Disks

Floppy Disks are made from circular plastic plates coated in iron oxide(which is a magnetic chemical).

Data is stored on the surface as patterns of magnetic spots.

Floppies are small and compact

They store up to 1.44Mb of data (about1/3 of an MP3 file)

They can be damaged easily by dust, dampness, electro/magneticpulses


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Hard Drive


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Hard Drive

Hard drives store data by writingmagnetic patterns onto metal disks.

The surfaces are divided up into sectorsand tracks which allows each part to beaccessed directly.

The disk is in a sealed box to prevent dust damage.The read/write head is just above the surface of the diskThe disk spins between 7,000 and 10,000 rpmThey hold gigabytes of data (most recently up to 750GB insize)


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Optical Backing Storage

Optical backing storage uses laseroptics to read and write data.

Data is stored in binary by using lasers toburn microscopic marks on the disksurface.

Data is read by reflecting light off thesurface to read the microscopic marks.


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CD-ROM

High Capacity - 650 Megabytes

Stores data in microscopic grooves

Read Only


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DVD-ROM

Works in the same way as CD-ROM

Stores more data because it uses a narrower laser beam toread and write to disk

Ordinary DVDs hold 4.7 Gigabytes

Double-sided, multilayered DVDs store up to 17GB

Enough space for large files such as movies


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CD-R

Stands for Compact Disk Recordable

Uses a layer of dye which laser changes to storedata

CD-Rs are WORM- Write Once Read Many

Once files are written on, they cant be deleted orchanged

CD-Rs are read-only after they are written


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CD-RW

Stands for Compact Disk Re-writable

Unlike CD-R, these can be rewritten

This is because they use the laser to change the reflectiveproperties of microscopic marks

CD-ROMS, CD-Rs and CD-RWs are used for: backing up large files

Storing large multimedia presentations Storing large programs, like games

CD-ROMS, CD-Rs and CD-RWs are slower than hard disks

But they are removable!


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DVD-R and DVD-RW

Works in the same way as CD-R and CD-RW

Stores more data because of narrower laser

Can store up to 4.7GB


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USB Flash drive

USB Flash drives are rewritable memory chips Store data just like a disk

Used as backup and plugs into USB ports on a computer

Very small and portable

Sizes from 64MB to 2 Gigabytes


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Input Devices

Input devices are pieces of hardware thatlet you control a computer by sendingdata to the computer from your device.


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Mouse

A mouse lets youcontrol the pointer onscreen, and click to

select icons.

Mice usually have 2buttons and sometimesa scroll wheel.


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Trackball

A trackball is similar toa mouse except the ballis on top. The trackball

does not move aroundthe desk like a mouse.

They are useful when auser does not have

desk space to move amouse, and for peoplewho find it hard to usetheir arms to moveobjects around.


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Trackpad

A trackpad is a smallpad that senses themovement of your

finger.

It lets you control themouse by moving yourfinger across the pad.

You can click bytapping the trackpad.


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Graphics Tablet

A flat plastic panel with electronic sensors below thesurface detect the movements of a pointing device.

Very accurate used by graphic artists / designers /Computer Aided Design (CAD)


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Touch Sensitive Screen

Simple to operate

Useful for public information systems

Tiring to use after a while

Not precise


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Keyboard

Input text and numbers

Function keys

QUERTY layout

Very common, nearly every computer has one


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Scanner

Input drawing, photographs from paper.

Light beam passes over page and asensor detects the reflection

Optical Character Recognition (OCR)software can recognise writing


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Digital Cameras


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Digital Cameras

Captures light coming through the lens andstores a digital image

Allows instant review of picture takenDelete photos you dont like

Takes a memory card can be various

capacities.


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Choosing acamera

Look at the accuracy (resolution) measured in Megapixels. 5 Mpx is enough

Does it have a zoom lens? Digital zoom isworthless because it produces poor pictures

What capacity is the memory card?


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Digital Video cameras

Same principle as still digital cameras

Need a large storage capacity video takes up a lot of space (15

frames per second)

Some have a small LCD screen toview your video

Features: zoom, focus, lighting,infrared recording, onboard editing


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Webcams

Same principle as digital videocamera

Connected directly to

computer via USB

Can put a webcam in awebsite

Useful for video calls via MSNMessenger

L P i t


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Laser Printer

Uses a laser beam to copy image of apage onto light-sensitive drum

Ink (toner) attracted to the drum then

transferred to paper

Laser printers are fast

The output is high quality

They are expensive to buy but relativelycheap to maintain.

S i k t th


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Inkjet Printer

Sprays ink onto the paper

Printout quality is high

Cheap to buy, can be expensiveto maintain (expensive ink)

Slower than Laser Printer


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Plotter

Uses inkjet technology toproduce large, accurate andcomplex drawings

Used by architects / designers

Quicker than drawing by hand


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Monitor

Screen used to displaycomputer output

Different monitors havedifferent resolutions

The higher the resolution,the more detailed thepicture will be

High resolution needed forCAD and art work


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LCD / TFT Displays

LCD = Liquid Crystal Display

These screens have the following advantages:

Flat, light, needing little power, can be runfrom a laptop battery

The one disadvantage is that sometimes theyare not bright enough and can cause eyestrain


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LCD / TFT Displays

TFT = Thin Film Transistor

Same advantages as LCD.Uses a tiny transistor to form each pixel

Can update the image very quickly, allowing it

to handle complex graphics and animationwhich LCD displays cannot

Compute Speake s


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Computer Speakers

Produce sound from the computer

Allow you to do multimedia presentations, video-

conferencing, games, music etcComputer speaker systems vary in quality andnumber of speakers depending on output wattage(RMS) or surround sound capability etc


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Desktop VS Laptop


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Desktop VS Laptop

Desktop computers stay in the sameplace. Laptop computers are portable

Because of this, the components usedneed to be light and consume lesspower (run off battery)

This means that a laptop with the same

specification (CPU speed, RAM) willcost more than a same spec desktop.


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Laptop

Laptop computers are small andcompact

They weigh a lot less than a desktop usually 1.5 3 kg

Runs off battery, charges from mains

Has a flat screen (LCD or TFT) Has a normal keyboard and trackpad


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Palmtop Computer

Is about the size of your hand

Small keyboard or a stylus

with handwriting recognition Stores data on a memory card

Useful for ultra-portablecomputing on the move

Store contacts, calendar,editing documents, email etc


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Mainframe computer

Large and powerful

Lots of processing power

(multiple CPUs) and RAM Many users connected using

terminals

Used by banks and other

large businesses to processand store data


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Multimedia Systems

Multimedia systems integrate sound, animation,video and graphics

Most modern computers have these capabilities

Interactive learning,

information systems,multimedia web pages,games


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Multimedia systems

A fast CPU and lots of

RAMand storage Quality TFT display

Scanner

Digital camera (video)

Surround soundspeakers

Data projector

A good system for viewing and creatingmultimedia might include:

Documents

MELJUN CORTES's - Computer System Lecture