input and output devices

1. 3.2-Input and output devices
3.2.1 Input devices

2. Input Devices
• Every computer system receives commands and data, from the real world, via input devices
• Input devices converts inputs into digital data which can be processed
• For conventional computer systems, such as desktop computers and laptops, the most common
input devices are the mouse and the keyboard
• There are a wide range of input devices used in more specialist computer systems such as
scanners and sensors

3. Barcode Scanner
•Barcodes are a series of black and white bars which represent a
code
How does it work?
•A barcode uses red laser to read the data it represents, the light from
the white lines are reflected back whereas black lines absorb the light
so less is reflected. The different levels of reflection are converted into
a binary value which can be processed by a microprocessor
Uses include:
•A barcode reader can be handheld or built into a larger machine such
as a self-service checkout at a supermarket
•Barcodes can be used in many ways such as identifying a
product being sold or tracking a package through the delivery
process
•Benefits include:
•faster checkouts, automated stock control, less chance of
error due to manual entry of data, and more detailed tracking
information

4. Digital Camera
• A digital camera works by capturing
light and converting it into a digital
image

5. • How does it works?
• Light enters the camera through the lens and
• It then reaches sensitive cell made up of millions of tiny sensors which are acting as
photodiodes (i.e. charge couple devices (CCD) which convert light into electricity)
• sensors are often referred to as pixels (picture elements) since they are tiny components that make
up the image
• the image is converted into tiny electric charges which are then passed through an analogue
to digital converter (ADC) to form a digital image, the ADC converts the electric charges from
each pixel into levels of brightness (now in a digital format)
• apart from brightness, the sensors also measure colour which produces another binary
pattern; most cameras use a 24-bit RGB system (each pixel has 8 bits representing each of the 3
primary colours), which means each pixel has a red value (0 to 255 in denary), a green value (0 to
255) and a blue value (0 to 255)

6. Uses include:
• Digital cameras are integrated into smartphones , used in security systems and by professional
photographers to create high quality digital images.
• Benefits include:
• An advantage of digital cameras is they show a preview of the image
• They also instantly create an image that can
then be easily duplicated and transmitted via bluetooth or WiFi
• Software can be used to edit digital photos, for example applying a filter or retouching a photo

7. Keyboard
• A keyboard is the most common device
used for text-based data input.
• Types:
1. physical keyboards connected via USB or Bluetooth
2. Smartphones and tablets have virtual keyboards
• How does it work?
Each key on a keyboard has a peg underneath it which
makes contact with a conducting membrane. This is
then converted into an electrical signal to transmit
a unique character code. The CPU refers to an index file
to identify which character the key press represents as
each character on a keyboard has a corresponding ASCII
value

8. Drawback:
1. Entry of data via a keyboard is a slow process which is also prone to error
2. Increased and excessive typing can lead to injuries such as repetitive strain injury (RSI).

9. Microphone
• A computer microphone works by converting
sound waves into electrical signals that can
be processed by the compute, so that it can
be stored, duplicated or modified.
• How does it work?
The microphone has a diaphragm that vibrates
in response to sound waves. These vibrations
are then converted into electrical signals by
the cone and coil of wire attached to the back
of the diaphragm. Changes in the signal are
recorded by a microprocessor using analogue
to digital converter

10. Uses:
• Microphones are used to record music, telephone calls, communicate online and dictation.
• Microphones are also used as a sensor (to detect sound in an intruder detection system), to input
text into a computer (of particular benefit to a disabled person)

11. Optical Mouse
A mouse use a laser to detect and track movement,
this is then processed by a microprocessor which
interprets the movement and replicates it
when moving a virtual cursor on-screen
Items can be selected or moved using the left mouse
button, whilst the right button usually displays
additional menus
They can be wired or wireless
Uses:
They are used to control the cursor in a Graphical
User Interface (GUIs)
Benefits:
• They are simple to use and provide the user with
an intuitive way to navigate the computer
• They are reliable due to no moving parts

12. Touch Screen
• A touchscreen can
be classed as both an
input device and an
output device

13. Type
How does it work
Benefits/Drawbacks Uses
Resistive screen Made up of two layers of polymer and glass. A
voltage is applied across the two surfaces. When the
top polymer surface is touched it makes contact
with the bottom layer completing a circuit allowing
current to flow at that point. The point of contact is
detected where a change in voltage occurred, which
enables a microprocessor to calculate the coordinates.
+ Cheap to produce.
+ Resistant to surface contaminants
+ Can be activated with nearly every object (stylus,
finger, gloved hand)
Used in cash machines,
information kiosks, medical
equipment
Infra-red screens Uses a glass screen and an array of sensors and
infrared transmitters. Where the infrared beam is
broken by a finger, the signal to some of the sensors is
broken or reduced thus allowing a microprocessor to
calculate where the screen was touched
+ Excellent image quality,
+ high precision
+ durable
+ allows for multiple touches at the same time
- Requires a bare finger or stylus for activation
-Can be sensitive to moisture on the screen or light
interference
Tablets, laptops, smartphones
Capacitive screens Relies on fingers touching the screen causing a
change in the electrostatic fields (change in current
flow). The point where the finger touches the screen is
calculated by a microprocessor. If projective
technology is used, multi-touch facility (pinching and
sliding) is allowed.
+Excellent image quality
+Unlimited touch-life
+Scale well
- Sensitive to interference from light, water
Large scale commercial displays
Information kiosks
Medical equipment
Touch Screens

15. QR code Scanner
A QR code is a visual representation of data using black and white
squares
QR codes can represent over 7000 digits whereas a barcode
represents up to 30 digits
QR codes are scanned by a camera (often on a mobile device)
How does it work:
A piece of software convert the squares into binary data
Uses of QR scanner:
• QR codes often link to a website where more information can be
found
• They can also be used to advertise products, share contact
details, provide promotional codes, train tickets, and event tickets

16. 2D Scanner
How does it work?
A two-dimensional (or flat-bed) scanner
the document is placed on a glass plate. A
light is then shone on the piece of
paper/documetnt and a light sensor used
to detect the light which is bounced
back. Reflected light is measured for each
pixel. This data is converted into binary
data so the document can
be digitally recreated​
Uses:
• 2D scanners can be used for
creating digital versions of documents
or photographs
• Reading passports at airports

17. 3D scanner
How does it work?
A three- dimensional laser scanner shines a light
over an object. The geometry and
dimensions are recorded so the object can be
recreated digitally​.
3D scanners can be used to create and modify
3D models for use with specialist software such
as computer-aided design (CAD) software.
A 3D printer could then print out the model,
creating replicas with 3D printers.
Uses
Typical uses of 3D scanners and printers are
dentistry, product development, medical

18. Questions

19. Useful Links:
• Microphone: How do microphones work? - Recording Explained - YouTube
• 3D Scanner: 3D scanner. How it works? - YouTube
• Laser Printer- https://www.youtube.com/watch?v=WB0HnXcW8qQ
• Secondary Storage (Optical, Magnetic, Solid-State & Cloud)-
https://www.youtube.com/watch?v=_0KIfGxp37E

20. 3.2.2 Output devices

21. Output Devices
Definiton: An output device shows the results of the processing in a way humans can understand
• In a general purpose computer system, the main output device is the monitor/screen
• Other output devices include projectors, printers, speakers and actuators

45. Summary

65. 3.3 Data storage

74. Secondary Storage

76. Optical
• Optical devices include CDs, DVDs and Blu-rays.
• Blu-rays have the largest capacity
• CDs have the lowest capacity
• CD-R are read-only (you cannot save data on to them)
• CD-RW can be written to and read from. In CD-RW the chemical
composition of the disk is changed to represent 0s and 1s. This
change can be overwritten
• DVD-RW can be written to and read from

78. • Magnetic hard disk drives have been the
main type of internal secondary storage in
personal computers for many years
• A magnetic hard disk is made up
of several metal discs coated with a
magnetic material
• These are called platters
• Iron particles on each platter
are magnetised to represent a 0 or 1

79. • The hard drive spins the metal disk(s) at a high speed
(typically around 5400-7200 RPM) using a motor
• A read/write arm, controlled by an actuator, moves
the head over the surface of the disc to the location
of the data​
• The data is read/written using electromagnets

80. • Solid State secondary storage is made
of transistors that are arranged in a grid layout
• It uses NAND and NOR gates in electrical circuits
to persistently control the flow of electrons
• Current flowing is 1, no current is 0 - which is
how electrical flow can represent binary values
• A NAND gate will take in two inputs and produce
an output (1/electrical current) as long as both
inputs are not 1
• A NOR gate will produce an output (1) only when
both inputs are 0
Solid State Drive

82. 3.3.4 Virtual memory:
Virtual memory is part of secondary storage which acts as RAM when RAM is full
• Why do we need virtual memory?
Case of when processes run out of RAM. If the amount of available RAM is
exceeded due to multiple programs running, it is likely to cause a system
crash.
• Solution:
This can be solved by utilising the hard disk drive (or SSD) if we need more
memory. This is the basis behind virtual memory. Essentially RAM is the
physical memory, while virtual memory is RAM + swap space on the hard
disk or SSD.

86. Benefits of VM
The main benefits of virtual memory are:
» programs can be larger than physical memory and still be executed
» there is no need to waste memory with data that isn’t being used
(e.g. during error handling)
» it reduces the need to buy and install more expensive RAM memory
(However there are limits to the value of doing this).

87. Drawbacks of VM
• Accessing data in virtual memory is slower
• Disk thrashing (HDD) – a problem in a hard disk drive (HDD) caused
by excessive swapping in and out of data causing a high rate of head
movements during virtual memory operations.
• The processing speed of the computer will be considerably reduced
due to continuous head movement. At thrash point, the execution of
a process comes to a halt since the system is so busy moving data in
and out of memory rather than doing any actual execution.

88. Terminologies:
• Paging – technique used by memory management to store
and retrieve data from HDD/SSD and copy it into RAM.
• Page is a fixed-length consecutive block of data utilised in
virtual memory systems.
• thrash point – the point at which the execution of a program comes
to a halt because the system is so busy moving data in and out of
memory rather than actually executing the program

94. 3.4 Network hardware
3.4.1 Network interface card (NIC)

109. • Routers and gateways (connects network to one another but
doesn't direct data packets) have a unique public address.
• Public addresses are assigned by your internet service provider and
are the IP address for the network. They are often static addresses
meaning they do not change
• Private IP addresses assigned by routers to devices connected within
its network. These are often dynamic IP addresses meaning they
can change. Dynamic addresses are assigned from a list of available
addresses at the time they are required

113. The IP4
system is
running
out of
possible
addresses
due to the
enormous
increase
in
networked
devices

114. • A new system called IPv6 has been developed.
• IPv6 provides enough unique addresses for every
networked device on the planet.
• IPv6 uses a 128 bit address. Digits are organised
into eight groups
• Each group is made up of four hexadecimal digits
Solution to IPv4's Limitation?

119. • A router being used to connect a LAN to a WAN will have a public IP address , which has been assigned to it by an
Internet Service Provider. It is this public IP address that other routers use to identify and direct packets to the network.
• An important role of the router is to analyse data packets and direct them on to their destination
• The IP address of both the sender and intended recipient is stored in the header of the data packet
• The header contains information about the packet
• The payload is the actual data being sent
• If the data packet is coming into the LAN, the router will send the data packet to the specific device, within its LAN, that
the packet is meant for.
• If the packet is being sent from a device within the LAN, it will read the header of the packet to determine the
intended destination IP address
• It will then forward the packet to the destination
• It might have to travel through several routers before it gets to its destination. Each pass from router to router is called
a hop
Packet Switching

123. Chapter 5: The Internet and
its Uses
5.1 The Internet and the World Wide Web (WWW)

131. URL
What is a URL?
• The URL is a text-based address that identifies the location of a
resource on the internet
• It is the address of a web page, image, video, or any other resource
available on the internet
• A URL looks like this: protocol://domain/path