Transcript Slide 1

The physical parts of a computer system are known as the
hardware. A single item of hardware is called a device.
A computer system can be drawn in a block diagram as follows:
Main Memory
ROM and RAM
Output
Input
Devices
Processor
Devices
Backing
Storage
Devices
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The Processor - where all the sorting, searching, calculating and decision making
goes on.
Modern computer systems have two or more processors working together to make
the system work better. You will find systems with duo-processors, with two
processors working together, and quad processors, with four processors working
together, and even a hexa-core processor with six processors.
Clock speed is one simple measure of how powerful a processor is.
Processors have different clock speeds measured in GigaHertz (1 Gigahertz(GHz)=
1000 million pulses per second). Faster clock speeds can improve performance.
HP Pavilion P6-2178EA Desktop PC Intel
Core i5 3.3GHz,
6GB RAM
3TB Hard disk drive
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Main memory is located inside the computer system.
Main memory can hold either RAM or ROM. Data can flow from main memory to the
processor (RAM and ROM) and data can flow from the processor to main memory (RAM
only).
ROM (Read Only Memory) is system memory. It holds vital systems information like
start-up instructions.
Key points about ROM
Data is stored permanently in ROM, it is not lost when the power goes off.
Data in the ROM cannot be changed.
Holds vital systems data and programs.
Data flows from ROM to the processor but not from the processor to ROM since
this memory is read only.
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RAM ( Random Access Memory) is the working space of the computer. It holds all the
programs and data files currently in use by the system and the user.
Key points about RAM
The processor can write to, or read from, RAM at high speed.
Data held in RAM can be changed.
All data in RAM is lost when the power is switched off.
RAM holds all the data and programs currently in use.
Data flows from RAM to the processor and from the processor to RAM.
Measuring the size of memory
Bit
Binary Digit: a single 1 or 0
Byte
8 bits e.g. 11001100
Kilobyte
1024 bytes
Megabyte
1024 Kilobytes
Gigabyte
1024 Megabytes
Terabyte
1024 Gigabytes
Petabyte
1024 Terabytes
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Converting between units:
To change:
Bits to bytes, divide by 8
Bytes to bits, multiply by 8
Byes to KB, divide by 1024
KB to bytes, multiply by 1024.
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Input Devices (needed to put information into the computer)
1. Keyboard
Virtual (software) keyboards are also available - an image of a keyboard is
displayed on the screen. Advantage; this can be very helpful to users with
limited hand movement. Laser keyboards are available where an image of a
keyboard is projected onto the desk.
Disadvantage; keyboard entry can be slow and sometimes errors can be made.
2. Mouse
Used to point to and select items on the screen.
3. Trackpad
As you move your finger over a touch sensitive pad the cursor moves
on screen. Often found on Laptop computers instead of a mouse.
Advantage; no desk space required to move a mouse.
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4. Joystick/Gamepad or Game Controller
These types of controllers are mostly used to play
computer games.
5. Graphics Tablet
Consists of a flat surface covered with sensors.
The user “draws”with a special pen called a stylus.
The image is then shown on screen.
Advantage; drawings created with a graphics tablet are much more
accurate than using a mouse or any other pointing device.
6. Touch Sensitive Screen
The user can make a selection or position the cursor by touching the
screen.
Advantages;
touch screens are simple to operate
usually found where normal keyboards would be difficult to use like
information points in public places
less likely to be damaged compared to mouse/keyboard.
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7. Scanner
A scanner is used to turn a picture on paper into a digital image in the
computer’s memory.
A light beam passes over the page and a sensor detects the light being
reflected.
The image is then stored in the computer as binary numbers.
Using character recognition software, text can be scanned in and put in
a word processing document and then edited.
The resolution (dpi-dots per inch) of a scanner is one measurement used
to determine how good it is.
8. Digital Camera
A digital camera captures images (pictures) and stores them as
digital files which can be transferred to a computer for editing
and printing. You measure how good they are by looking at the
number of megapixels they have (resolution) and how much
memory they have (capacity).
The amount of data that can be stored on the camera is usually
measured in megabytes or gigabytes.
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9. Digital Video Camera
Digital video (DV) is a method of recording moving pictures
in a digital format. A digital video camera captures these
very high quality images. These images can be transferred
directly to a computer’s memory for editing.
10. Webcam
A webcam is a low cost, low quality video camera, used on the web
to provide online video.
11. Microphone
Used for sound recording on a computer system to use in
presentations, websites or podcasts.
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Output Devices (needed to display the results of processing)
1. Ink Jet Printer
This sprays tiny drops of ink onto the paper to form characters or
graphics. Printouts can be black and white or in colour.
Advantages:
Produces high quality pictures.
Fairly cheap to buy.
Portable versions are available.
Disadvantages:
Running costs (The cost per page) are high as it is expensive to
replace the ink cartridges and they only hold enough ink for a few
hundred pages.
They are also slow to print.
Printouts can easily become smudged if they are handled too
quickly after printing or allowed to get wet.
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2. Laser Printer
A laser printer puts very fine powdered plastic (called toner) onto the
paper to make its image.
Advantages:
very fast
high quality output
text and graphics can both be printed.
cost per page is low as each toner cartridge can produce
thousands of pages.
Disadvantages:
laser printers are more expensive than inkjet printers to buy
not portable.
Colour laser printers are also available but can be expensive to buy and
to run.
You can compare printers according to the following characteristics:
Speed: how fast they print, measured in pages per minute (ppm)
Resolution: the higher the resolution the better the quality. Resolution is measured in
dots per inch (dpi).
Cost: the initial cost of buying a printer/Version
running
costs: cost of toner or ink.
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3. Monitor
The screen used to display computer output. The screen is made up of
picture elements or pixels.
Liquid Crystal Display (LCD) are light, compact screens that don’t need
a lot of power and can easily be run on batteries. They are used on
desktops, laptops, palmtops and smartphones.
Thin Film Transistors (TFT) is a type of LCD screen that uses lots of
transistors to produce a high quality display. A TFT screen can display
animations and 3D graphics much more clearly than ordinary LCD
screens.
4. Loudspeakers/Headphones
Speakers/ headphones on your computer enable you to play and
hear sound. They can be separate devices or are built into the
computer.
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5. Graphics Card
A graphics card is a device which controls the quality of output
on a monitor.
Graphics cards often contain a large quantity of RAM and can
support different types of screen displays at a variety of
resolutions.
They have their own processor which then frees up the main
processor so that it can get on with other tasks.
Advantage; a good graphics card can speed up game play on a PC,
as the processor no longer has to work out what the screen should
look like and display it.
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6. Sound Card
A sound card is a device used to take in sound and for outputting
sound.
Sound cards are capable of outputting a number of sound channels
in high quality formats.
They have a dedicated processor which then frees up the main
processor so that it can get on with other tasks
Advantage; sound cards improve the quality of sound output from
games and multimedia applications.
Sound is analogue in nature, it is a continuously varying quantity. Computers work in
digital quantities. In order to input sound into a computer the sound must be changed
from analogue into digital. This process is called analogue to digital conversion.
A microphone or another sound source is connected to the computer’s sound card in
order to capture the sound. The sound card carries out the ADC in the process called
sampling.
In order to output sound from a computer the sound must be changed from digital to
analogue. This process is called digital to Version
analogue
conversion.
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Backing Storage Devices
We store things we want to use again using a backing storage device.
Backing storage is used to store programs and data permanently.
Remember that RAM is the working area of the computer but all
contents of RAM are lost when the computer is switched off so we
need to store our work on backing storage.
USB Flash drives, Hard disks, CD-ROMs and DVDs are examples of
backing storage media and the hardware that uses or holds the
media is known as a backing storage device.
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Magnetic Storage
1. Hard Disk Drive
A sealed metal disk inside the drive which stores data on its surfaces using
magnetic charge. They are usually fixed inside a computer, but you can
get external drives that you plug into the computer usually via a USB port.
Advantages
You can read and write data to a hard disk
Fast access times
Fast data transfer rates
Cheap per Gigabyte.
2. Portable Hard Disk Drive
A portable hard it is small enough to carry with you .
Portable hard drives can be easily used by multiple PC’s for file sharing .
A portable hard drive allows for backups of files ( a backup is a second
copy of a file).
A portable drive allows for quick and easy storage of data.
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3. Magnetic tape Unit
Tape storage can be used as a form of backing storage. Tapes store data
in binary using magnetic spots to encode the data.
Key Features:
They have a large capacity.
They are ideally suited for making backups.
However magnetic tape drives are being used less and less now. Many
companies are backing up their data on to a mirror disk. This is
basically another hard disk drive that takes an exact copy of the current
drive and therefore acts as a backup of the system.
4. Cloud Computing (external storage)
Cloud computing is the use of the Internet to provide computing services.
Cloud computing customers can rent storage space on servers.
Customers can have a contract which enables them to decide how much storage
space they need for their data. This arrangement can be very flexible and
customers can easily scale their storage up or down as required.
They can also access a wide range of application software. As soon as the
contract is signed a customer can have access to all the software it needs without
having to buy the hardware or pay for and install the software.
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Optical Storage
Optical disk drives use laser technology to read data from the
disks or write data to the disks.
The drive for optical media uses a low powered laser to read the
data from the disk. If it is a writeable disk then it uses a higher
powered laser to write to it.
The speed of an optical CD ROM drive is given as a number, for
example 52x ( 52 times 150 kilobits per second where 1 kilobit
equals 1024 bits). This speed refers to the transfer of data from
the disk to the computer’s main memory.
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1. CD-ROM (Compact Disc – Read Only)
This means the information can be read by a computer but cannot be
added to or altered. A standard CD-ROM can store up to 700Mb of data.
Advantages
Capable of storing a large amount of data.
Fast access.
Disadvantage
Cannot be used to store new documents or to make changes to old
ones
2. CD-R (Compact Disc – Recordable)
This is a CD-recordable, it allows you to record or write data once.
Once data has been recorded on it, it works just like a CD-ROM, it is
read only.
The speed of a CD-R drive is given as two numbers, the read speed and
the write speed.
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3. CD-RW (Compact Disc Re-Writable)
The contents of the disk can be erased and replaced with new data. A CD-RW
has three speeds, one for writing the data, one for re-writing and one for
reading. For example write 52X, re-write 24X, and read 52X.
4. DVD-ROM (Digital Versatile Disk-Read Only Memory)
A DVD is similar to a CD-ROM but has much greater storage capacity. The capacity is big enough
to store digital video of full-length feature films or huge amounts of data. A single-sided singlelayered DVD can store 4.7 Gigabytes. Double-sided multi-layered DVDs have a capacity of 17
Gigabytes.
The speed of a DVD-ROM drive is given as a number, e.g. 16X. This is different from a CD, as each
1x is 1250 kilobits per second (kbps), so 16x is 16 x 1250 kbps.
5. DVD-R (Digital Versatile Disk-Recordable)
A DVD –R allows you to record data once. After recording the data cannot be changed. They have
the same capacity as DVDs but have two speeds, one for writing and one for reading data e.g. write
6x, read 12x.
6. DVD-RW (Digital Versatile Disk-Re-Writable)
Similar to a CD-RW, these come blank and its contents are written with a DVD re-writer. The whole
disk can be erased and re-used many times over. A DVD-RW has three speeds, one for writing data,
one for re-writing and one for reading. Eg. Write6x,re-write
2.4x and read 12x.
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Solid State Storage
USB Flash Drive (pen drive, memory stick)
This is a small portable backing storage device.
An easy way of making backups and transferring data between
computers.
Digital cameras use solid state storage in the form of flash cards to
store images captured by the camera.
Solid State devices are:
 Small - flash cards can fit inside a camera, USB flash drives can fit on a key ring and in
watches.
 Robust because they have no moving parts.
 Use less power than a hard disk drive
 Have a range of capacities.
Over time the cost of these devices has decreased and the capacity of them has increased.
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Types of Data Access
Sequential access (serial access) means when you
want to go from file A to file Z in a sequential access
system, you must pass through every file.
It is used when loading a file from magnetic tape.
Random/direct access is when the read head
goes straight to the data.
It is used when loading a file from a disk.
A disk drive is called a random access device
because the disk drive head can read data in any
order.
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Software is the name given to the programs that run in a computer.
A program is a set of instructions that tell the computer what to do
eg. MS Word, iTunes.
The operating system is a program or set of programs that
controls the hardware and software running on the computer
allowing the user to communicate with the application software
and hardware devices.
When a computer is switched on the first task is to load the
operating system into RAM.
There are a number of different operating systems eg. MacOS X,
Windows 7, Android.
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There are different ways that an operating system helps us:
Error reporting
When we use the mouse, keyboard, trackpad or trackball, the operating system
looks at what we have asked and tries to do it. If we ask for something that is not
possible then it will report an error. e.g. trying to save a file with a filename being
used by another file that is still open.
File management
This organises and manages the saving and loading of program files and data
files between the backing storage device and the main memory. It decides
which tracks on the Hard disk a file should be stored on.
Memory management
This organises the programs and data in the main memory of the computer. It
makes sure that there is enough space in the RAM to store a file and decides
where the files should be stored.
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Representation of Data
Storing Numbers
A single unit in Binary is called a bit. The word bit is made up from the two words BInary
and digiT. It can have a value of 1 or 0.
For example: Binary number with 8 bits - 1011 0011
To change this number to decimal use the place values for binary;
128s
1
64s
0
32s
1
16s
1
8s
0
4s
0
2s
1
1s (units)
1
This would be 128 + 0 + 32 + 16 + 0 + 0 + 2 + 1 = 179 in decimal
Largest 8 bit number is 1111 1111 which is 255 in decimal
Range of Integers - If 2 bytes (16 bits) are used to store numbers then numbers from 0000
0000 0000 0000 up to 1111 1111 1111 1111 may be stored (0 to 65,535 in decimal- a total
of 65,536 different numbers.)
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Storing Text
A character is a symbol or letter eg. digits 0 to 9, letters and punctuation marks.
The character set is a list of all the characters which a computer can process and store.
A byte is the space in a computer’s memory which is used to hold one character. Each
character is stored using a different binary code number eg. 0100 0001 is the letter A.
One form of code is the American Standard Code for Information Interchange or ASCII.
Each ASCII character takes up one byte of storage. Many different computers use ASCII to
represent text.
Advantage; this makes it easier for text to be transferred between different computer
systems.
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Some ASCII characters do not print on the screen in the normal way. They are known as
control characters because they control certain operations of the computer system.
In ASCII, codes from 0 to 31 are used as control characters. The table below shows an
example of ASCII codes.
Character
Enable printer
Return
Binary
000 0010
0000 1101
Decimal
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Unicode is another code to represent letters but uses 16 bits.
This allows more characters to be represented eg. Different languages have lots of
different symbols.
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A program is a set of instructions that a computer can understand.
A High Level Language program is a program written in everyday language eg. PRINT
“Hello”
Machine Code is a the computer’s own language. Machine code is a program written
using binary eg. 00001101 00011011 11010111
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Storing Graphics
Bit mapped Graphics
Graphics, like any information displayed on the screen, are made up of tiny dots called
pixels. Pixel is short for picture element.
Bitmap representation of graphics means that each pixel in a graphic is represented by a
series of bits/bytes.
Black and White graphics can be stored using ones and zeros:
A shaded square
A blank square
can be represented by a 1
can be represented by a 0.
Resolution refers to the number of pixels on the screen.
The more pixels on the screen, the better the picture.
More memory is needed for high resolution graphics.
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Low resolution
High resolution
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