External Hardware Devices

Question 1

Barcodes

Answer 1

• Printed diagrams consisting of light and dark portions
• Consist of data that is readable by a barcode reader

Question 2

2D barcodes

Answer 2

Contain more information in the same amount of space as a 1D barcode, however require more processing

Question 3

Components of a barcode reader

Answer 3

• Laser light source
• Lens
• Photodiodes
• Mirror

Question 4

Barcode reader

Answer 4

• A laser beam is shone onto the barcode
• The mirror moves the beam across the barcode
• Dark areas of the barcode absorb light; light areas reflect it.
• Reflected light passes through the lens and hits the photodiode
• The photodiode measures the light and converts it into an electrical signal.
• The electrical signal is processed into a digital binary signal that represents the encoded data.

Question 5

Digital camera

Answer 5

• A lens focuses light onto a sensor
• The sensor converts incident light into an electrical charge
• The sensor is made up of cells, representing a pixel in the final image
• A shutter regulates the path of light between the lens and sensor

Question 6

Colour cameras

Answer 6

There are multiple cells for each pixel, each of which has a filter that only allows in certain wavelengths of light

Question 7

Bayer filter

Answer 7

A filter with the same number of green filters as red and blue combined and
allows a camera to produce a closer approximation of what the human eye sees

Question 8

Laser printer

Answer 8

• An output device that produces images on paper from digital signals, printing entire pages at once
• Consists of a laser light source, a mirror, a positively charged drum, a toner roller and fusers
  The laser is directed at the drum’s surface by the mirror to discharge parts, leaving
  behind an impression of the page in electrical charge
• The toner roller dispenses negatively charged toner onto the drum, with the toner attracted to the positively charged portions of the drum and applied to the
  paper
• The paper is heated by fusers, fixing the toner to the paper
  ● Colour printers apply the same process with four different colours of toner: cyan,
  yellow, magenta and black (CYMK)

Question 9

RFID

Answer 9

• A method of transferring information wirelessly between a tag and reader
• The reader emits radio waves which are detected by the tag’s antenna and powers the chip
• The chip will send back a radio wave containing its stored information which the reader can receive and decode

Question 10

RFID tags

Answer 10

• Contains a chip with a small amount of memory and a coil of wire attached to the chip that functions as an antenna
• They are usually passive, inducing enough power from the reader to operate the chip
• However, they can be active (containing a small power supply)

Question 11

Primary storage

Answer 11

Main memory (ROM/RAM)

Question 12

Secondary storage

Answer 12

Non-volatile memory used to store files and applications

Question 13

Hard disk drives

Answer 13

• Consists of a number of circular platters made from a magnetic material
• Each platter has an actuating arm with a mounter read/write head that changes the magnetic polarity of parts of the platter
• Data is written in a series of concentric tracks divided into sectors

Question 14

Capacity of HDDs

Answer 14

Can be increased by:
- Adding more platters
- Decreasing the width of tracks

Question 15

Solid State Drives

Answer 15

• Consist of non-volatile NAND flash memory cells and a controller that manages the structure of the drive
  -The memory cells are made of floating gate transistors that store information by trapping electrical charge
• Data is stored in pages, combined to form blocks
• Not capable of overwriting data so pages must be completely erased before writing new information

Question 16

Optical disks

Answer 16

• Store information that can be read by a laser
• Can be read-only or rewritable
• Has a single continuous track that spirals out from the centre of the disk

Question 17

Read-only disks

Answer 17

• Stores data using pits (burnt into the disk by a high-powered laser, permanently deforming the surface)and lands
• A low-power laser beam is passed over the surface, reflecting light back to the photodiode when the incident is on a land
• The pattern of reflections and scatters can be converted to a digital signal

Question 18

Rewritable disks

Answer 18

• The pattern of reflections and scatters is created by a dye on the disk’s surface
• The phase-change dye can be converted multiple times between transparent and opaque