Internal / External Devices !! Flashcards
Explain the operations of an SSD
- Consists of NAND flash memory cells and a controller that manages the structure of data on the drive
- NAND flash memory is non-volatile.
- Memory cells are formed of floating gate transistors that store information by trapping electrical charge.
- The presence of trapped charge or absence indicates 0 or 1
- Data is stored in pages, which are combined to form blocks.
- SSDs are not capable of overwriting data, instead the controller must completely erase the entire page before writing new info.
What is NAND flash memory?
Non-volatile memory, meaning that the SSD’s contents are retained even when there is no power being supplied.
What are the advantages of an SSD?
- No moving parts: suitable for devices that would experience a lot of movement (phones, tablets, laptops)
- No moving parts: capable of higher read/write speeds than HDDS
Explain the operations of a Digital Camera.
- Light enters through a lens. Light intensity is recorded by sensors (CCD)
- Each sensor produces an electrical signal
- The signal represents a pixel
- An ADC converts measurements of light intensity into binary
- A colour filter is applied to generate separate data values for red, green and blue colour components.
What are some advantages of digital cameras?
- Film is not required
- Image can be easily edited using editing software
- Can immediately check and retake an image, the image doesn’t need time to develop.
What are some disadvantages of digital cameras?
- Initial cost of a digital camera is usually higher than a film camera
- Digital storage can be lost -> doesn’t produce a physical copy
- Digital cameras become out-of-date much faster than film cameras.
Explain the operations of a Laser Printer.
- Bitmap of image is built in memory from page description
- Negative charge is applied to photosensitive drum
- A laser beam is directed at the drum
- A mirror is used to direct the laser beam, where the laser strikes the drum the charge is neutralised.
- Negative charge is applied to the the toner
- Paper is passed over drum and toner is transferred to it.
- Positively charged transfer roller assists transfer of toner from the drum to the paper.
- A heater fuses toner onto paper.
What are some advantages of laser printers?
- Low cost per printed page
- It prints many pages per minute
- No wet pages
What are some disadvantages of laser printers?
- Higher initial costs
- Expensive to repair
- Higher power consumption
Explain the operations of a barcode reader.
- An oscillating mirrors directs light from a laser onto a printed barcode.
- The light reflected by the barcode passes through the lens and is incident on the photodiode.
- The photodiode turns light into electrical charge.
- This electrical charge is measured and processed into a digital signal representing the content of a barcode.
- Light portions of a barcode reflects the most light, dark sections absorb incident light. This corresponds to binary 1s and 0s.
How do barcodes detect errors?
Barcodes have parity bits and check digits built in, allowing computers to tell if a barcode has been read correctly.
What happens if a barcode reader fails to scan a barcode?
The reader will continue to scan until the barcode is read successfully.
Why are 2D barcodes (QR codes) better than 1D barcodes?
2D barcodes can contain more information in the same amount of space as a 1D barcode.
It requires more processing in order for the info to be extracted.
What are some advantages of barcodes?
- Increases accuracy of receiving product info
- Reduces training time for businesses
- Low cost -> companies can create a limited number of barcodes for a low price.
What are some disadvantages of barcodes?
- Needs direct light in order for the barcode to be seen
- Needs to be close to the barcode to be scanned
- Must be scanned individually
Explain the operations of RFID.
- An RFID tag contains a chip with a small amount of memory,
- The chip is attached to a coil of wire that acts as an antenna
- RFID tags can be passive or active:
- When the RFID tag is scanned, the tag emits radio waves that are picked up by the tag’s antenna.
- Power induced in the tag’s antenna from the waves is enough to power the chip.
- The chip then uses its antenna to emit its own radio wave with information on the chip.
- The wave from the tag is picked up by the reader.
- The wave is decoded into information and returns the info to a computer system.
What can Passive tags do?
Passive tags can induce enough power wirelessly from the reader to operate the chip.
Must be within a few centimetres of the reader.
What can Active tags do?
Active tags contain a small power supply, like a battery.
Can be used much further away from readers.
What are some advantages of RFID ?
- Data on RFID systems are usually secure as it takes specialised equipment to read the data.
- RFID tags can read multiple tags simultaneously -> increasing efficiency.
- Automates data collections, which vastly reduces human effort and errors.
What are some disadvantages of RFID ?
- RFID tags are usually larger than barcode labels
- The coverage of RFID is limited to ~3 metres.
- More expensive than barcode systems.
Explain the operations of an optical disk.
- An optical disk is made up of pits and lands.
- Pits are burnt into the disk by a high power laser, which permanently deforms the surface.
- When a low power laser beam is passed over the flat surface of a disk, it reflects back onto a photodiode.
- When the laser is incident on a pit, the light from the beam is scattered in different directions - NOT back in the photodiode.
- Resulting pattern of reflections and scatters are converted into a digital signal of binary 1s and 0s.
What are recordable and rewritable optical disks made of?
- A pattern of reflections and scatters is created by an opaque dye on the disk’s surface.
- When there is no dye, the disk reader’s laser beam is reflected off the disk’s surface.
- Where there is dye, the laser beam is absorbed by the dye and not reflected.
What kind of dye does recordable optical disks use?
- Uses a special photosensitive dye.
- This changes from opaque to transparent under a high power laser.
- This is used to write information to the disk.
- The dye remains unaffected by the low-power laser used to read the disk.
