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Higher Computing: Unit 1: Topic 4 – Peripherals
Higher Computing
Topic 4
Peripherals
St Andrew’s High School, Computing Department (4-2-12)
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices
Keyboards
As well as the traditional QWERTY
keyboard you should realise that
there are alternative designs that
are specialised to carry out less
traditional tasks. An example is the
Dvorak keyboard.
St Andrew’s High School, Computing Department (4-2-12)
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices - Scanners
•The flatbed scanner can normally work
with documents up to A4 size. When a
document is scanned the resultant digital
representation of the scanned image is a
bit map.
•Accuracy is a measure of how close the
computer image representation is to the
original. This is influenced by the
resolution and bit depth capability of the
scanner.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices - Scanners
•Resolution is measured in dpi (dots per
inch).
•An image with a resolution of 600 dpi
that measures 4 inches by 6 inches will
have:inches x inches x dpi x dpi
=4 x 6 x 600 x 600 bits (pixels)
=8640000 bits / 8
=1080000 bytes / 1024
=1054.6875 Kb
=1055 Kb to store the file
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices - Scanners
•Bit depth describes the number of bits
that is used to store the colour of a pixel.
For example, 8 bits can represent 256
colours. Most scanners nowadays have a
bit depth of 24 bits; this means that each
pixel can have one of 224 colours.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices - Scanners
•A scanned picture measures 5 inches by
4 inches and has been scanned by a
scanner with a resolution of 600 dpi and a
bit depth of 24 bits. How much storage
would be required for the scanned image?
inches x inches x dpi x dpi x colours
=5 x 4 x 600 x 600 bits x 3 bytes
=21600000 bytes / 1024
=21093.75 Kb / 1024
=20.599 Mb
=21 Mb to store the file
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(24 bits = 3 bytes)
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices – Digital Cameras
•A digital camera is one of the fastest
ways to use pictures into a computer. No
need to develop film or scan images from
a printed copy. Pictures are ready to use
right away in presentations or send in
email messages. It is possible to print at
home and achieve photo quality results.
•Digital photos are bit maps, made up of
thousands or millions of pixels with values
to represent image brightness and colour.
Digital image data is stored in a memory
card inside the camera.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices – Digital Cameras
•Accuracy is measured by the resolution
and bit depth capability of digital camera.
•In cheaper range cameras the resolution
is of VGA standard i.e. 640 x 480 pixels,
capturing 307,200 pixels in each picture.
•Other cameras support "megapixel"
representation, able to take highresolution shots at 1024 x 768 or 1280 x
960 pixel resolution.
•Most cameras have a bit depth of 24 bits
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices – Sound Cards
•Sound is an analogue signal and needs to
be converted to a digital form to be able
to be stored/used by a computer.
•Digital representation is achieved by
sampling the sound. The more often a
sample is taken, the sampling frequency,
and the more data that is stored about
each sample, the sample size, the better
the quality of sound that is represented.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices – Sound Cards
•How closely the digitised sound matches the
original will clearly depend on the sampling
frequency and sample size.
•The higher the sample frequency and the more
bits used per sample, the closer the digital
representation will be to the original analogue
form.
•Sound is stored directly to disk and so it does
not really make sense to talk of the capacity of
a sound card. As with all digitisers, you should
be aware of the amount of backing storage that
will be required to hold the data permanently.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Input Devices – Sound Cards
•A simple calculation with a sample
frequency of 44.1 kHz (CD quality), a
sample size of 16 bits, lasting for 2
minutes requires:
Number of Samples
Number of Bytes
Required
=44100 x 120 (secs)
=5292000
=5292000 x 2 bytes
=10584000 bytes / 1024
=10335 Kb / 1024
=10.09 Mb
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Higher Computing: Unit 1: Topic 4 – Peripherals
Output Devices – Inkjet Printers
•Resolution is typically 300 to 600 dots
per inch. They support the printing of
text and graphics, colour and a range of
shades. Speed is pretty slow with a range
of 4 pages per minute to 8 pages per
minute, depending upon the model.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Output Devices – Laser Printers
•Resolution is typically 300 to 600 dpi,
although higher resolutions are available
if you are prepared to pay the price.
Colour and a range of shades are
supported. Speed ranges between 4 pages
per minute and 40 pages per minute.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Output Devices – Monitors
•Scan Rate – number of times the screen is re-drawn.
That is the number of times it scans from the top of
the screen to the bottom per second. This rate needs to
occur at least 50 times per second, (50 Hz) to stop
screen flickering.
•A video graphics adapter sets the scan rate and some
manufacturers provide adapters with different screen
proportions and resolutions. A resolution of 640 x 480
pixels (VGA) will require a different scanning rate than
a resolution of 800 x 600 pixels (SVGA).
•Multiscan monitors are able to deal with these
different scanning frequencies.
•TFTs are flat panels common in desktops/laptops.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Buffers
•A buffer is an area of RAM (computer
memory), normally on the device eg printer. It
is allocated to transferring data between the
computer and a peripheral. A buffer will be used
when a fast acting part of the system is
exchanging data with a slow acting device. The
buffer stores data until it can be dealt with.
For example, a printer operates at a much
slower speed than the computer. A program can
continue operating without waiting for each
Buffers store data after the data has been
character to be printed if the data is sent to a
received
(data
received
by a printer
andbystored
buffer.
The
buffer
is normally
managed
the
and waitssystem,
till it is which
printed
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operating
sends
printer when it is ready to receive data.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Spoolers
•When large amounts of data are to be sent to
a peripheral device, or when the peripheral is
shared across a network then spooling is a
preferred method of coping with the difference
in speeds of the processor and the peripheral.
•Spooling involves the input or output of data to
fast backing storage (eg disk). This, for
example, allows output to be queued from many
different programs and sent to a printer by a
print spooler (special operating system
software).
The data
print before
spooleritstores
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Spoolers store
is sentthe
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queue
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and
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for the
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is files
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sent to
the
printer when it is ready, using a print queue.
printer).
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – Hard Drive
(Magnetic)
•All the sectors around the disk, equidistant
from the centre, form a track. With multiple
platters, the collection of tracks on each
platter, equidistant from the spindle is called a
cylinder. When data is to be read or written,
the read and write heads are moved to the
appropriate track, where they wait until the
relevant sector spins past.
•Speed
•The speed of access to data stored on a hard
disk depends on the rotational speed and the
type of interface being used, for example,
SCSI.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – Hard Drive
(Magnetic)
•Capacity
•Hard disks have improved tremendously in
their capacity to store data in the last 10 years.
Many of today’s PCs have 80Gb hard disk drives.
•Access
•The hard disk is a direct access device,
meaning that data can be directly read or
written to any portion of the disk.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – Tape Storage
(Magnetic)
•Storing data on tapes used to be the only
solution to backing up hard disks of large
capacity. Tape is read and written on a tape
drive. This drive winds the tape from one reel
to the other causing it to move past a
read/write head.
•Capacity
•Magnetic tapes have large capacities, typically
up to 20 Gb.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – Tape Storage
(Magnetic)
•Access
•Tapes are sequential access devices, which
means that to get to a particular block of data
on the tape, it must go through all the
preceding blocks of data. Accessing data on
tapes is therefore much slower than accessing
data on disks.
•Not suitable when data needs to be used
regularly - disk is more appropriate. Because
tapes are so slow, they are generally used only
for long-term storage and backup.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – CD-ROM, R, R/W
(Optical)
•The most common optical storage device is the
CD-ROM. Read-only medium whose contents
cannot be altered once data is written to it.
•The read-only limitation of CD-ROMs has been
overcome by the creation of writeable CDs. CDRs can be written to once with a CD-Writer, and
CD-RWs can be written to many times using a
CD re-writer.
•Capacity
•CD-ROMs are typically 650/700 Mbytes in
capacity.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Backing Storage Devices – CD-ROM, R, R/W
(Optical)
•Speed
•In a single speed CD reader, audio data can be
read adequately, but is very slow for motion
video or large image files. Multiple speed CD
readers, such as 48xCD-ROM or 24xCD-ROM
can read these types of files properly.
•Write and Rewrite speeds are also multiples of
the single-speed rates. For example, a rewritable drive advertised at x48 x16 x4, means
that it can read CD-ROMs at x48, write once to
CD-R at x16 and re-write to CD-RW at x4.
•Access is Direct
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Higher Computing: Unit 1: Topic 4 – Peripherals
Solid State Storage Devices
Solid-state storage devices are made up
entirely from electronic components i.e. they
have no moving parts. They are also called RAM
disks, as they take the place of a magnetic disk
as a mass storage device. They can be in the
form of a plug-in card or cartridge containing
memory chips. The chips of a SSSD are
typically static RAM or Electrically Erasable
Programmable ROM (EEPROM or Flash EPROM).
•SSSD are used with devices where space is at
a premium e.g. in a camera, or when portability
is desirable e.g. a USB flash drive.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing
Interfacing hardware means making the
appropriate connections so that two
pieces of equipment can communicate or
work together effectively.
This section considers the 4 factors that
have to be resolved between the devices
before communication can happen.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Data Format Conversion
• Data to be communicated has to be
arranged in such a way to be understood by
the hardware or software doing the sending
or receiving. The data format may have to
be converted from
–
–
serial to parallel and vice versa eg keyboard
input (serial) needs converted to parallel
or from analogue to digital and vice versa eg an
analogue input sensor on a robot must converted
to digital using (ADC). For an analogue output
device eg motor the signal must be changed from
Digital to Analogue (DAC).
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Voltage Conversion
• Voltage is the electrical force that
allows devices to work. It is also
required to send data signals between
devices. As devices operate and send
signals at differing voltages then
these quantities must be changed to
allow successful communication.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Protocols Conversion
• A protocol is a set of rules that govern
the transmission of data. Certain
standards are set to allow for
successful communication.
• The standard (or protocol) will dictate
things like data format, timing, voltage
levels etc required by devices to allow
for data exchange.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Status Signal Handling
Status signals are messages passed
between the processor and peripherals.
Status signals can confirm that data has
been sent/received. Status signals
confirm whether a device is ready to
send/receive data. Eg the status of a
hard disc must be established before the
processor sends data to be written to the
disk, the disk may be reading data
already, the processor must delay
transmitting the data until the status of
the hard disc changes to idle.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Not in Arrangements
Interfacing - Buffering
• Different devices send and receive
data at different rates. If a device
sends data at too high a rate, then the
receiving device must cope with that,
possibly by buffering the data, ie,
storing it until it is able to deal with it.
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Types of Interfaces
• The type of interfaces that are in use
today include:
Interface
Serial
Parallel
USB
Firewire
Typical Use
Mouse/Keyboard
Old printers
Current printers, digital
cameras, etc
Digital video
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Slow
Fast
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Higher Computing: Unit 1: Topic 4 – Peripherals
Interfacing - Wireless Communication
• At the moment the move is towards wireless
technology – wireless keyboards, mouse, etc.
Wireless communications can be achieved
using WAP (Wireless Application Protocol).
This, like any protocol, is a set of
communication rules to standardise the way
that wireless devices can be used.
• Typically, wireless communication allows
communication between devices in a short
radius of about 10 metres. One such
technology is Bluetooth.
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