External Hardware Devices Flashcards
How does a laser printer work?
Print drum coated in positive charge
Laser beams reverse charge on parts of the drum via rotating mirror
Toner given positive charge, sticks to negative parts of drum
Paper rolled over drum
Toner fused to paper by heated rollers
How does a barcode reader work + check digit?
Laser shone at barcode by oscillating mirror
Light reflected back at different intensities (white/black stripe)
CCD sensor records light
Light converted into electrical signal
The data is passed through a function to calculate check digit, if the calculated check digit does not match the one scanned there is an error
How does a digital camera work?
Light enters camera focused by lens, regulated by shutter onto CCD sensor chip
Each CCD sensor has a colour filter to detect one colour
charge builds up in CCDs
Charge measured by CCDs
Signals from CCDs converted to binary
Stored as digital image
How does RFID work?
When RFID tag is scanned, it is powered up by the scanner via an antenna.
Once the tag is powered, it emits a radio wave
This contains the information held on the chip
This is picked up by the scanner and processed
How do hard disks work?
Read write arm over spinning platter
Data written in tracks, divided into sectors
What is an SSD made of?
Consists of NAND flash memory cells which trap electric charge
How do optical disks work?
Store information read or written by a laser
Data stored as pits or lands burnt into the disk
Read by measuring light reflected by low power laser (pits scatter more light)
How do CD-Rs work
Clear dye layer covering its surface, write laser makes it opaque, permanent
How do CD-RWs work
Clear dye layer covering its surface, write laser makes it opaque, changes transparency based on temperature
