7.4 External Hardware Devices

Question 1

Definition of Barcodes

Answer 1

Printed diagrams that use light and dark patterns to contain information that can be scanned and interpreted by a computer.

Question 2

Difference between 2D and 1D Barcodes

Answer 2

2D barcodes can encode more information in the same space but take more processing power by the computer.

Question 3

What do barcode scanners consist of?

Answer 3

Light source, lens, photodiodes, and a mirror.

Question 4

How do barcode scanners work?

Answer 4

• mirror directs the light onto the barcode.
• Light reflected by the barcode passes through the lens and is detected by the photodiode, which reads the reflections as electrical charge.
• This electrical charge can be read as a digital signal.

Question 5

Preventing Barcode Errors

Answer 5

• Parity bits/Checkdigits
• If it fails to scan properly, they can quickly rescan as a barcode scanner can scan 1000 codes a second

Question 6

Digital Camera Components

Answer 6

• Consists of a lens that focuses light on a sensor
• Path of light btwn lens and sensor is regulated by the shutter.

Question 7

Two sensors commonly used in digital cameras

Answer 7

• Complemtary Metal Oxide Semiconductor (CMOS)
• Charge Coupled Device (CCD)
• They both convert incidental light into electrical charge
• Charge builds up in cells, representing a pixel
• Once a photograph is taken, the charge in each cell is measured and converted into a digital value, which is stored.

Question 8

Coloured Cameras

Answer 8

• Multiple cells for each pixel
• Each cell for each pixel has filters that allow only certain light wavelengths to pass through
• Stores the value of the intensity of each colour as seperate images which can be combined to make a full coloured photo.

Question 9

Bayer Filter

Answer 9

• Closer approximation to human eyes
• Has the same number of green cells as red and blue cells combined

Question 10

Laser Printer Definition and components

Answer 10

• Output device that creates images on paper from digital signals
• Consist of laser light, mirror, drum, toner roller and fusers.

Question 11

Process of Laser Printers

Answer 11

• The drum is positively charged at the beginning
• The laser is directed by the mirror at specific parts of the drum, converting those sections into negatively charged areas and creating an impression of the page
• Toner is negatively charged and rolled onto the paper. As opposites attract, it is attracted to the positive parts of the paper.
• The paper is then heated by the fusers to fix the toner in place.
• Coloured printers have CMYK toners.

Question 12

RFID Def

Answer 12

• Stands for Radio Frequency IDentification
• Method of transferring data wirelessly between a tag and the reader

Question 13

Components of RFID

Answer 13

a chip containing a small amount of memory connected to a coil which acts as an antenna

Question 14

Passive v. Active RFID

Answer 14

• Most are passive
• Passive induct electricity from the sensor wirelessly
• Active tags have a small battery supply
• Passive RFID can only work from a short distance whereas Active RFID can be used over a large distance

Question 15

What is secondary storage

Answer 15

Storage used to store files and applications.

Question 16

How Hard Disks Work

Answer 16

• Consists of a number of circular platters which are made from a magnetic material
• These platters are split into concentric tracks and further divided into sectors.
• an actuating arm hovering above it, which acts a read write head.
• The platters rotate thousands of times per minute allowing for fast read/write speeds

Question 17

Capacity of a Hard Drive

Answer 17

• Between 500 GB and 5TB
• Adding more platters and decreasing the width of the tracks increases their capacity in the same size

Question 18

Advantages of Hard Disks

Answer 18

• High capacity
• Average speed

Question 19

Disadvantage of Hard Drives

Answer 19

• Has moving parts which can be damaged
• High power consumption
• Not portable
• High latency
• Unsuitable for portable devices like phones

Question 20

Structure of a Solid State Drive

Answer 20

• Consist of NAND flash memory cells and a controller
• The NAND Flash memory cells are formed of floating gate transistors which store information by trapping electrical charge
• The controller manages the structure of data on the drive.
• NAND flash memory is non volatile (memory is retained when there’s no power)
• Data is stored in books, further subdivided into pages.
• SSDs are not capable of overwriting data. Instead, the controller completely erases an entire page of the SSD before writing new info

Question 21

Advantages of SSDs

Answer 21

• High speeds
• Low latency
• Lightweight
• No moving parts
• Low power consumption

Question 22

Disadvantages of SSDs

Answer 22

• Low capacity
• Expensive

Question 23

Structure of Optical Disks

Answer 23

• Store information which can be read optically by a laser
• Contains pits and lands which records the binary values
• Pits are burnt onto the disk by a high power laser, permanently deforming the surface
• When a low power laser passes over the lands of the disk, it reflects back onto a photo diode.
• When a lower power laser passes over the pits of the disk, it scatters in different directions.
• This can be used to convert the pits/lands into binary

Question 24

Structure of Writable Optical Discs

Answer 24

• A pattern of reflections and scatters are created by opaque dye on the disk’s surface
• When there is no dye, the light is reflected onto the photodiode. Where there is dye, the light is absorbed by the dye.
• The dye changes from opaque to transparent under a high power laser, which allows for information to be written to the disk.

Question 25

Advantages of Optical Disks

Answer 25

• Cheapest option
• Very small and lightweight

Question 26

Disadvantages of Optical Discs

Answer 26

• Very low capacity (max of 25 GB on Blu Rays)
• Slow read write speeds
• High latency
• Can be damaged by dirt and scratches
• High power consumption.