1. Secondary Storage Devices

2. Secondary Storage Devices
Optical Media: CD ROM
(Compact Disc Read Only Memory)
The diagram below shows how data is retrieved from a compact disc.
Label
Protective layer
1.2 mm
Aluminium reflective metal layer
Data written on a continuous spiral track
Polycarbonate Plastic
The pits are impressed into the material on a continuous spiral track that, if it was unwound would be about 3.5km in length.
The data is read by bouncing a laser off the surface of the disc. The pits reflect the light, whereas the lands disperse the light. This represents the digital binary storage required to store data.
Pits
Lands
Laser Beam
Secondary Storage Devices

3. Secondary Storage Devices
Optical Media: CD ROM
(Compact Disc Read Only Memory)
Laser sled 1
Sliding rails 2
Motor 3
Disc hub 4
Lens 5
Polycarbonate 6
Pits 7
Reflective material 8
Protective Coating 9
Label surface 10 11
Lands
Secondary Storage Devices

4. Secondary Storage Devices
Blu-ray Disc
The diagram compares the different lasers that are used to extract information using a red or a blue laser as shown.
Secondary Storage Devices

5. Secondary Storage Devices
Blu-ray Disc
Different media are able to store different amounts using the different wavelengths of light.
Secondary Storage Devices