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Transcript of 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: