External Hardware Flashcards
1
Q
Barcode Reader Components
A
- Laser
- Lens
- Photodiode
- Mirror
2
Q
How does a barcode reader work
A
- Mirror directs laser onto barcode
- Light reflected passes through lens onto photodiode
- Lighter areas reflect more light: 1s and 0s
- Error detection with parity bits and check digits
3
Q
How does a camera work
A
- Light is focused onto sensor through a lens
- Sensor is commonly either CMOS or CCD
- Charge builds up on cells —> corresponds to pixels
- Multiple cells per pixel for each colour
4
Q
Laser printer components
A
- Mirror
- Laser
- Drum
- Toner roller
- Fusers
5
Q
How does a laser printer work
A
- Drum starts positively charged
- Laser discharges areas where ink is needed to be
- Toner roller applies negativley charged toner onto the drum
- Drum rolls onto paper
- Repeat for different inks
- Fuser heats it up to fix the toner to the paper
6
Q
How does RFID work
A
- Contains a chip with a small amount of memory
- Chip is attached to wire coil to act as antenna
- Passive tags have power induced wirelessly from reader
- Active tags have a small power source
- Reader emits radio waves that are received by antenna
- Induced power causes radio wave to be emitted by chip
- Reader decodes information
7
Q
HDD
A
- Magnetic platters
- Actuating arm with a read/write head
- Changes magnetic polarity of different parts of the platter
- Data is written on concentric tracks
- Tracks divided into sectors
- Can be damaged by movement
8
Q
SSD
A
- NAND flash memory cells + controller
- Cells are made of floating-gate transistors that can trap electrical charge
- Data is stored on pages which are combined into blocks
- Data cannot be overwritten: whole page must be erased before writing new information
- No moving parts: much faster
9
Q
Optical Disk (read only)
A
- Pits and lands burnt in by laser
- Lower power laser passes over surface, only lands reflect back to photodiode
- Corresponds to 0s and 1s
10
Q
Rewritable Optical Disks
A
- Same as read-only, but dye is used rather than burning
- Dye is photosensitive: if a high power laser hits it, it can change from opaque to transparent
11
Q
Nyquist Theorum
A
Sample Rate when sampling a sound must be double the highest frequency
