Secondary Storage
Cards (19)
- A magnetic disk is often referred to as a hard disk.
- An SSD is an electronic device that uses flash memory
- Optical discs are a large family of different disc types
- Hard Disk Drives
- Have Circular Platters made out of magnetic materials
- There is a actuating arm that reads and writes
- The Arm changes the polarity (north/south), when you save work.
- Data is written in tracks, divided into sectors
- Platters rotate 1000 times a min.
- Adding more platters to a HDD increases the capacity of the drive.
- Solid State
- Has NAND flash memory cells
- Has controller that manages structure of data and cells
- Memory cells store info by trapping electric charge through floating gate
- Data is stored in pages, groups and blocks
- Controller erass page before writing new info
- Optical Disk
- Have 1 continous track that spins at high speeds
- A laser beam hits the surface of the track
- If laser hits land and reflects back to the photoelectric cell - creates binary value 1
- If laser hits pit photoelectric cell has no reflection - creates binary value
- Barcode Readers:
- Light from laser is directed at the barcode pattern
- Sensor detects intensity of light
- Digital Cameras:
- When image captured
- It breaks up image into grid of pixels
- RBG filters are used to seperate wavelengths
- RFID - Radio Frequency ID
- A RFID is used for security,banking and shipping
- Passive RFID - not active until connected to reciever
- Active Tag - Always on and sending signals
- RFID
- Sensor pad emits radio energy
- RFID antenna picks up waves
- RFID chip becomes energised
- RFID chip sends identification
- Chip recieves new data
- Disadvantage of RFID is the cost as it requires more expensive equipment than barcode scanners.
- Advantages of RFID over barcodes are that they can be read from far away and do not need line of sight.
- Barcodes are printed onto products using ink or laser printers
- NAND flash memory is non volatile
- Data is SSD is stored in pages, which form blocks