Input/Output devices
Getting a computer to communicate
Input - Keyboards
QWERTY Keyboards are the most
common I/O device
Based on old typewriter designs
Can be slow to type with if not trained
Each key has an ASCII code
Input – Concept Keyboards
Typically found in shops and restaurants
They have keys with symbols on them to
represent different functions
E.g. if you order a burger at McDonalds
the assistant will press the picture of the
burger
Input – Mouse
Pimple
2-3 buttons which can be clicked to select
items on screen
The mouse has aTrackpad
ball in it which rotates
when it is moved, sending the direction to
the computer
Laptops use trackpads, trackerballs or
pimples which are all used to replace
mice as they are smaller
Input – Graphics tablets
Make drawing and handwriting easier
Use a touch sensitive tablet and a stylus
(like a pen)
The user presses the stylus on the tablet
and the position and pressure are sent to
the computer
Input – Joysticks
Used to play computer games or move
robot devices i.e. hospital body scanners
The joystick is on a firm base but can be
moved in any direction
The direction of movement is sent to the
computer
Input – Scanners
Converts a picture to digital data. The
computer builds up a map of the picture
based on bits of data for each pixel.
These BITMAP files are massive and take
up too much memory, but they can be
edited easily
Scanners are fixed (flat bed) or portable
(hand held)
Other Input devices
Digital camera – works like a scanner
Laser scanners – for reading barcodes
Video digitiser – works like a scanner for
video
Touch sensitive screens – instead of
pressing the key you press the screen
Microphones – convert analogue sound to
a digital version
Other Input devices
Sensors – for recording temperature, light,
infra-red etc.
Touch tone telephones – sends a tone
down the phone line, used to control
automated customer services, etc.
MIDI instruments – stands for Musical
Instrument Digital Interface and is a way of
recording music from an instrument
entirely digitally
Output Devices
The devices computers use to
communicate with you
Output – VDU
VDU stands for Visual Display Unit
CRT – Cathode Ray Tube, old fashioned,
bulky but cheap. Can cause eye strain.
LCD – Liquid Crystal Display, thin, modern
but expensive as each pixel has to be built
Output – Dot Matrix Printers
A blast from the past!
They work by using a series of pins to hit
an ink ribbon and get a series of dots onto
the paper. These dots make up the image.
They are the cheapest printer but very
slow, noisy and have poor resolution
They can be used to produce multi-part
printouts e.g. Using carbon paper to
produce copies of payslips
Output – Ink Jet Printers
Ink jet printers are commonly used in the
home
They spray a jet of ink in certain patterns
onto the paper to get the image
The printouts will run if they get wet
They are cheap to buy, have good
resolution and are quite small
They are slow to print and expensive to
run
Output – Laser Printers
These work in the same way as
photocopiers, by using electrical charges
to force ink to be rolled only onto certain
parts of a page
Expensive to buy the equipment and toner
cartridges (contains the ink) but cheap to
run (about 1p per page)
Very high resolution and very fast
 Cant use continuos or multipart stationary
Which printer is best?
Depends entirely on circumstances
Usually we say that an ink jet printer is a
good compromise as it is cheap but had
high resolution
For high resolution, crisp, high volume and
fast printouts then laser is the best
If cost is a major factor or
multipart/continuous stationary needs to
be used then dot matrix is the best
Output – Speakers
Sound output can be Real or synthesised
Real sound is stored on a computer as a
digital representation of the actual sound
It can be processed and output through
the speaker (digital – analogue
conversion)
Written text in ASCII can be converted to
synthesised sound via Speech synthesis
This helps people with visual impairment
It doesn’t sound very human
Other output devices
CAM – Computer Aided Manufacture,
takes a computer based design and builds
it using robotic machinery
LASER CAM and Card Layer Printers
work in the same way but use specialised
equipment to produce the output. Laser
CAM carves with Lasers and CLPs use
slices of card to produce the final model.
Actuators – control physical movement, so
are things like motors, hydraulics, etc.
Storage - Bits and bytes
A computer only understands
the numbers 0 or 1, or
whether a switch is on or off.
We call those 1s and 0s ‘bits’ –
binary digits.
A byte (made up of 8 bits) is
enough computer memory to
store a single character of data
(e.g. the letter F).
The computer uses a code to understand what each bit
pattern means.
Using the ASCII code, for instance, the letter F is 70
and has a bit pattern of 01000110.
Read Only Memory (ROM)
When a computer is first switched on, it needs to load
up the BIOS (Basic Input/Output System) and basic
instructions for the hardware.
These are stored in ROM (Read Only Memory).
This type of memory is
called non-volatile because
it retains the data.
Data stored in ROM remains
there even when the
computer is switched off.
ROM can be found on the
motherboard.
Random Access Memory (RAM)
Computers store temporary data in the RAM (Random
Access Memory). These could be operating instructions, loose
bits of data or content from programs that are running.
The contents of RAM are constantly rewritten as the data
is processed.
When the computer is
switched off, all the data is
cleared from the RAM.
This type of memory is called
volatile because it only
stores the data whilst the
computer is switched on.
RAM sticks are found on the motherboard.
Backing storage – hard drives
The hard disk of the computer stores the
system information, programs and data
that the computer uses every day.
Computer servers will use RAID systems
with many hard drives to provide huge
capacity and safer storage. The drives
can be mirrored so that data written to
one of them is also written to others, so if
one drive fails, the others just take over.
Removable hard drives plug into the
USB port and can be used for backup or
transfer of data to another computer.
Backing storage – optical
There are two main types of optical storage: CD and DVD.
They look exactly the same, but DVDs hold much more
data than CDs and need different drives to read them.
CD-ROMs are read only – you can read data
from them but can’t write more data to them.
CD-Rs allow you to write data once, but you
can’t write over it.
CD-RWs allow you to write data and then
record new data over it.
DVD-Rs and RWs follow the same pattern.
You need special software to write to CDs
and DVDs – you cannot simply copy files to
them.
Backing storage – flash memory
In recent years, flash memory has become much more popular.
It holds a lot of data in a very small space.
It doesn’t need special software to use it.
Most computers will recognize the device
as soon as you plug it in.
Flash memory sticks connect through
USB or FireWire ports.
Many other devices, like digital cameras
and MP3 players, also use flash memory.
Flash memory cards can hold different
types of data so your MP3 player could
hold a data file with your homework on it,
for example.