Topic 7.4 External Hardware Devices Flashcards
What is the purpose of a Barcode Reader
To identify the products being purchased
How does a Barcode Reader work
- 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
What is the purpose of a Digital Camera
Device that takes photos and stores them in a digital format
How does a Digital Camera work
- 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
What is the purpose of a Laser Printer
Produces images on a paper from digital signals
How does a Laser Printer work
- 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
What is the purpose of RFID
Used to transfer information wirelessly between a tag and a reader.
Used in contactless debit cards and hotel room cards.
How does RFID work
- 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
What is the need for Secondary Storage in a Computer System
In main memory, data is lost when the computer turns off.
In secondary storage, the data and programs are kept indefinitely.
How does a Hard Disk Drive (HDD) work
- 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
How does a Solid-State Drive (SSD) work
- 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
How do Optical Disks work
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
Compare the Capacities of the Secondary Storage Devices
HDD - VERY high capacity (500GB - 5TB)
SSD - relatively low ( >1TB)
Optical Disk - VERY low ( >25GB)
Compare the read/write speeds of the Secondary Storage Devices
HDD - Relatively good = 100MB/s
SSD - VERY good = 500MB/s
Optical Disk - Very low = 30MB/s
Compare the Latency of the Secondary Storage Devices
HDD - High
SSD - VERY low
Optical Disks - High
Compare the Portability of the Secondary Storage Devices
HDD - Bad - Bulky and Heavy
SSD - Good - Lightweight & Rarely damaged
Optical Disks - Average - Lightweight but can be damaged by scratches
Compare the Suitability of the Secondary Storage Devices
HDD - Desktop Computers & Servers
SSD - Laptops & Phones
Optical Disks - Music / small amounts of data