Topic 7.4 External Hardware Devices

Question 1

What is the purpose of a Barcode Reader

Answer 1

To identify the products being purchased

Question 2

How does a Barcode Reader work

Answer 2

• Barcodes on the product contain the information
• Mirror directs the light from the Reader onto the barcode
• Light is reflected by the barcode and passes through the lens
• Light is turned into an electrical charge
• Electrical charge is measured and processed to form a digital signal containing the contents of the barcode

Question 3

What is the purpose of a Digital Camera

Answer 3

Device that takes photos and stores them in a digital format

Question 4

How does a Digital Camera work

Answer 4

• Shutter opens (LOL)
• Lens of the camera focuses light onto a sensor
• Sensor converts light into electrical charge
• Each electrical charge represents a different pixel in the image
• Charge is converted to a digital value and stored as a digital image

If colour camera
- Multiple cells for each pixel in the image

Question 5

What is the purpose of a Laser Printer

Answer 5

Produces images on a paper from digital signals

Question 6

How does a Laser Printer work

Answer 6

• Drum is positively charged everywhere
• Laser is directed onto the drum by the
  mirror
• Places on drum where laser hit lose their
  charge (neutral or 0 charge)
• Negatively charged toner is put onto the
  positive charge parts of the drum
• Toner applied to paper from the drum
• Paper is heated, fixing the toner to the paper

Question 7

What is the purpose of RFID

Answer 7

Used to transfer information wirelessly between a tag and a reader.
Used in contactless debit cards and hotel room cards.

Question 8

How does RFID work

Answer 8

• Chip inside the RFID tag contains small amount of memory.
• When tag is scanned, the reader emits radio
  waves to pick up the tag’s chip
• Power from these waves is enough to power
  the chip
• Tag emits its own radio wave which contains
  the information
• Reader picks up wave and returns information to the computer

Question 9

What is the need for Secondary Storage in a Computer System

Answer 9

In main memory, data is lost when the computer turns off.
In secondary storage, the data and programs are kept indefinitely.

Question 10

How does a Hard Disk Drive (HDD) work

Answer 10

• Consists of a number of circular platters.
• Above each platter there is a read/write head
• Platter spins rapidly so read/write head can access / add data quickly
• To increase capacity you can add more platters

Question 11

How does a Solid-State Drive (SSD) work

Answer 11

• Consist of NAND flash memory cells
• And a controller that manages the structure of data on the drive
• Data is stored in pages
• When data needs to be overwritten, the whole page must be completely erased

Question 12

How do Optical Disks work

Answer 12

Pits and Lands
- Pits burnt into disk by laser
- Light is sent onto the disk
- If light reflects diagonally, means it is changing from land to a pit
- If light reflects straight up means it is staying as it is
- So can be read in binary as a pit = 1 and land = 0

Question 13

Compare the Capacities of the Secondary Storage Devices

Answer 13

HDD - VERY high capacity (500GB - 5TB)

SSD - relatively low ( >1TB)

Optical Disk - VERY low ( >25GB)

Question 14

Compare the read/write speeds of the Secondary Storage Devices

Answer 14

HDD - Relatively good = 100MB/s

SSD - VERY good = 500MB/s

Optical Disk - Very low = 30MB/s

Question 15

Compare the Latency of the Secondary Storage Devices

Answer 15

HDD - High

SSD - VERY low

Optical Disks - High

Question 16

Compare the Portability of the Secondary Storage Devices

Answer 16

HDD - Bad - Bulky and Heavy

SSD - Good - Lightweight & Rarely damaged

Optical Disks - Average - Lightweight but can be damaged by scratches

Question 17

Compare the Suitability of the Secondary Storage Devices

Answer 17

HDD - Desktop Computers & Servers

SSD - Laptops & Phones

Optical Disks - Music / small amounts of data