Explain how data is written to and read from a hard disk drive

1. There is magnetic disk.
2. Disk has many platters.
3. Disk is continually spinning.
4. Each platter has its own drive head.
5. Drive head moves radially in and out and "parked" when not in use.
6. Data is store in concentric tracks, tracks are made up of sectors of data.
7. Here a positively magnetised regions and negatively magnetised regions.
8. A change from positive to negative represents a 1 and a magnetised region is a 0.

Explain how data is written to and read from an optical disk.

1. High-powered laser burns pits into CD surface on single spiral track.
2. A low-powered laser reflects light on surface.
3. Pits and land, reflect light back into the sensor, which is read as 0.
4. A change from pit to land and vice versa, does not reflect light back into the sensor which is read as a 1.

Explain how data is written to and read from a solid state drive.

1. SSDs have NAND flash memory and controller module.
2. Memory cells are made from floating gate transistors.
3. Floating gate transistors trap charge, where trapped is 1 and not trapped is 0.
4. One SSD has many blocks and one block contain many pages.
5. To overwrite data and entire page must be erased before new information can be written into it.

State the factors of comparison between digital storage mediums.

1. Maximum capacity.
1. Hard disk drives → highest capacity → up to 12TB.
2. SSDs → low capacity → normally under 2TB
3. Optical disk drives → Lowest capacity → Single Sided Blu Rays up to 25G.
2. Read/Write Speeds.
1. SSDs → 500MB/s → Very fast.
2. Hard disk drives → 100MB/s → Good.
3. Optical Disk → 30 MB/s → Very slow.
3. Portability.
1. SSDS → Lightweight, no moving parts so resistant to movement.
2. Optical disks → Lightweight, easily scratched.
3. Hard drives → bulky, heavy, easily damaged by movement.
4. Power Consumption.
1. SSD → very low.
2. Hard disk drive + Optical disk → high.
5. Latency.
1. SSD → very low.
2. Hard disk drive + Optical disk → high.

Explain how data is read from a bar code, and state why its suited to some applications.

1. A bar code is strip of alternating black and white stripes.
2. A laser is shone at a mirror, which directs it towards the barcode.
3. Light portions reflect incident light, while dark portions absorb incident light.
4. Reflected light is read as 0 and no light is read as 1 by a photodiode behind a lens.

Useful because of built in checking methods: parity bits, check digits and millisecond read speeds.

Explain how an colour image is captured using a digital camera.

1. Incident light rays are focussed onto a CCD by a lens.
2. CCD is divided into a number of cells representing a pixel.
3. Each cell produces a larger voltage depending on the intensity of light reaching it.
4. There are multiple cells for each pixel, each behind a different colour filter.
5. The filter only transmits certain wavelengths of light.
6. Each image is combined to form a full colour image.

Explain how a laser printer works.

1. Laser is shone at mirror, which reflects ray onto drum.
2. Drum is positively charged and laser discharges regions.
3. This leaves an impression on the drum.
4. A toner roller dispenses negatively charged toner onto drum and is attracted to remaining positive regions on drum.
5. Drum presses toner onto paper.
6. Paper is heated to fuse toner to paper.

Explain how passive RFID system works.

1. Radio waves emitted by reader pass through coils on tag.
2. Electromagnetic induction generates enough power for microchip to transmit data through the same coil.
3. Reader decodes information.

Compare active RFID systems to passive RFID systems.

1. Passive RFID systems require no batteries on tags, but have a shorter effective range.
2. Active RFID systems require batteries on tags, but have a longer effective range.