Computing Science
National 4 & National 5
Unit 1
Information Systems Design & Development
Topic 7d
Input, Output, Backing Storage & Interfaces
N4/ N5 Computing Science
Input, Output, Backing Storage & Interfaces
Contents
Contents................................................................................................................... 2
Introduction ............................................................................................................. 3
Input Devices ........................................................................................................... 3
Modern Input Methods ............................................................................... 4
Output Devices ........................................................................................................ 5
LCD / TFT monitors ...................................................................................... 5
Inkjet and Laser Printers .............................................................................. 6
Backing Storage ....................................................................................................... 7
Solid State Backing Storage Devices ............................................................ 8
Sequential and Random Access ................................................................... 8
Interfaces ............................................................................................................... 10
Hardware Interfaces .................................................................................. 10
Software Interfaces ................................................................................... 10
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Input, Output, Backing Storage & Interfaces
Introduction
Computers use a variety of different input and output devices to allow us to
communicate with it in many different ways. As computers can come in different shapes
and sizes, these devices have also changed in size and shape to make it more practical to
work with it. For example a keyboard on a desktop PC is a lot larger from a keyboard on
a touch screen phone, although performing the same task.
Input Devices
A piece of hardware is an input device if it sends information to the computer. It can
capture a range of inputs including key strokes, sound, graphics and video.
Input Device
Picture
Purpose
Mouse
To move the cursor on the monitor and
select items by clicking on them.
Touchpad
Detects movement of a finger to move the
pointer on screen. It can also detect finger
taps to select items. They are found on
laptops to save connecting a mouse.
Keyboard
Used for manually typing data into a
computer.
Microphone
This allows the computer to capture
sound, such as a person talking. They are
usually built into computers today.
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Webcam
Scanner
Input, Output, Backing Storage & Interfaces
This is used to capture video. Some will
come with a built in microphone in case
your computer does not have one, so it
can capture sound too. A webcam is used
for video conferencing. Most webcams are
built into computers now. Resolution is
used to measure the quality of a webcam.
Resolution is measured in DPI (Dots Per
Inch).
This allows you to input hand drawings,
photos or text into the computer. It will
then create an electronic copy of it.
Resolution is used to measure the quality
of a scanner.
There are many other input devices such as games controllers, remote controls and
interactive whiteboards etc. For the purpose of this course you only need to know the
ones listed above.
Modern Input Methods
Eye-tracking technology has been developed for mobile phones. This will automatically
scroll down when it detects the user’s eye looking at the bottom of the screen, and vice
versa. It can also be programmed to automatically pause videos when the user looks
away from the phone. You can read about a phone like this here:
http://www.bbc.co.uk/news/technology-21791023
Activity
What is a QWERTY keyboard?
The letters on a keyboard seem to be laid out in a random order. Research the Internet
to find out how the keyboard letters ended up in the order that they appear and write
your answer below.
Create a poster on computer input devices. Your poster should include a variety of input
devices from the table above and any other input devices that you wish to include.
Remember, many of these devices will come in many different forms such as these
computer mice:
http://www.hongkiat.com/blog/unusual-computer-mice-you-probably-havent-seenbefore/
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Input, Output, Backing Storage & Interfaces
Output Devices
An output device allows data to be displayed or passed out of a computer. Data can be
output in many ways including visually, aurally or on paper.
Output Device
Monitor/Screen
Speakers/Head
phones
Printer
Plotter
Picture
Purpose
Used to display the output of a computer
on a screen. Most computers today use
LCD (Liquid Crystal Display) technology.
Resolution is used to measure the quality
of a monitor. Resolution is measured in
DPI (Dots Per Inch).
These are used to output sound for the
user to hear.
Used for outputting data onto paper. This
is known a hardcopy (electronic copies are
known as softcopies). There are 2 types of
printers that you will learn about in the
pages that follow. They are measured by
how fast they print pages (Pages Per
Minute) and their resolution, again
measured in Dots Per Inch.
A plotter is an output device which draws
pictures using coloured pens.
LCD / TFT monitors
Liquid Crystal Display (LCD) monitors have very thin layers of liquid crystal between
sheets of thin glass. A backlight creates light that passes through the first piece of glass.
At the same time, electrical currents cause the liquid crystal molecules to align to allow
varying levels of light to pass through the second piece of glass and create the images
you see. LCD screens are found on a variety of things including laptops, calculators,
digital watches, microwaves etc. One big advantage of an LCD screen is that it does not
require a lot of power.
Thin Film Transistor (TFT) is a type of LCD technology. They have very good resolution
and response times.
This video describes how LCD technology works:
http://www.youtube.com/watch?v=k7xGQKpQAWw
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Inkjet and Laser Printers
Most printers today are either inkjet printers or laser printers. Inkjet printers work by
propelling droplets of ink onto the paper. The ink needs to be fast drying so it does not
smudge when the person picks it up. Inkjet printers use ink cartridges which can be
easily replaced when the ink runs out.
Laser printers use a laser beam to project the image of the page onto the drum inside
the printer. A powder, known as toner, is then placed on the paper and heated rollers
then melt and seal the toner onto the paper.
Both printers can print high resolution images, however the main difference between
them is that laser printers can print much faster.
Activity
Most computer monitors made today are LCD screens. What does LCD stand for?
What is the difference between a hardcopy and a softcopy?
What is used to measure the quality of an image on a monitor? What is it measured in?
If you had to print off a 30 page document and you had the choice of an inkjet printer or
a laser printer, which would you choose and why?
What device outputs information by using coloured pens?
What are the 2 main criteria that should be looked at when comparing printers?
With a budget of £500, find one inkjet printer and one laser printer and compare them
on their different features before recommending the best one for a school library.
Printer Type
Laser Printer
Inkjet Printer
Printer Name
Resolution
Pages per minute
Cost
Recommendation
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Backing Storage
Backing storage is a way of permanently storing programs and data. We need backing
storage because when we switch off the computer all the data in RAM, Random Access
Memory, is lost. When we write data to backing storage, we often say that the data is
being saved. When we read data from backing storage, we say that the data is being
loaded from backing storage.
There are different backing storage devices including:
Backing
Storage Device
Picture
Description
Hard Discs
Capacity varies from around 20 GB to 2 TB.
Mainly found inside the computer base,
but portable drives are available.
Magnetic Tape
Although old, this is still used today mainly
for backup purposes. It is very cheap and
reliable, although it can take a long time to
load data from it.
CD-R
Optical storage around 700 MB. Uses a
laser to read and write information to disk.
DVD-R
Optical storage around 4.7 GB. Uses a laser
to read and write information to disk.
Blu-Ray
Optical storage of around 25 GB. The name
Blu-Ray Disc refers to the blue laser used
to read the disc, which allows information
to be stored at a greater density than is
possible with the red laser used for DVDs.
Storage capacities of CD, DVD-R and Blu-Ray discs will vary as they can be recorded on
both sides. DVD and Blu-Ray discs can also be recorded on dual layers on the same side.
The storage capacities in the table is for single sided and single layer recording.
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Solid State Backing Storage Devices
USB Flash
Memory
These devices vary in capacity typically
between 128 MB to 1 TB. They are small in
size, therefore very portable. These
devices are known as a solid state devices.
Flash Cards
(such as SD and
Micro SD cards)
Solid state devices are robust because they have no moving parts, therefore they are
unaffected by movement. This makes them ideal for MP3 players and digital cameras so
that people can walk/run with it, without it being effected, making it very reliable.
Sequential and Random Access
Sequential access only allows the data to be read into the computer in the same order
in which it was saved (i.e. in a sequence). Magnetic tape is an example of sequential
access.
Random or direct access allows the user to access data or files on any order. Examples
of random or direct access:




USB Flash drives
hard discs
DVDs
CDs
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Activity
Input, Output, Backing Storage & Interfaces
Amy needs to save her school work on a portable storage device so that she can work on
it at home. The work is approximately 200 MB in size. Suggest all suitable backing
storage devices that Amy would be able to use for this task. (assuming that the
computers that Amy will be using are fitted with disc drives and have available USB ports
and card slots)
Magnetic tape is an old technology. Suggest a reason why it still popular today.
Karen has accidently deleted an important file from her works file server. Luckily the file
can be recovered as it was backed up on a hard disc. Describe why the file can be
recovered faster from the hard disc than if it was backed up on magenetic tape.
Optical storage can come in the form of CD-R’s or DVD-R’s. Reaserch why a DVD-R has a
much larger capacity than a CD-R.
Describe what is meant by a solid state backing storage device?
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Interfaces
So far we have looked at many different input, output and backing storage devices. All of
these devices operate in different ways but they must all be able to communicate with
the computer in a way that they both understand. For example a person who only
speaks English would struggle to communicate with another person who only speaks
German. We would solve this problem through an interpreter. Computers solve this
problem by using an interface. Interfaces go between the computer and a device so
they can work together. This compensates for the differences between how they
operate.
Hardware Interfaces
A hardware interface is the physical point where the device connects to the computer.
Most devices you probably use connect through a USB port although there other ports
including VGA or HDMI (for monitors and projectors etc) or SD card slots.
Software Interfaces
A software interface is the software that the computer needs to install so that it can
communicate with the device. For example when installing a new printer, the computer
needs to install the printer driver for that particaulr printer.
So what does an interface need to deal with?
Data Conversion: computers use digital signals but the majority of its peripherals and
communication in the outside world are in analogue signals. To make sure the
computer understands the information converters are used. An Analogue to Digital
Converter (ADC) is used when signals come into interface and Digital to Analogue
Converter (DAC) when signals go out from the computer.
Speed: devices send and receive data at different rates and the interface needs to set it
so both the computer and the device has the right speed.
Data Storage: An area to store data until the slower peripheral device is ready to
accept it. For example, a printer buffer is required as the processor can send many
pages at once and the printer is too slow to deal with them. The CPU puts them in the
buffer and can get on with other work as the printer prints from the buffer at its own
speed.
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Status Information: provide information on the current state of the device. For
example a printer interface will provide information such as ready to accept more data
or out of paper etc.
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