5.1 Flashcards
CDs and DVDs are described as?
optical storage devices (laser light is used to read and write data from the surface of the disk)
what do CDs and DVDs use to store data?
a thin layer of metal alloy or light sensitive organic dye is used to store data
How do they work (CD and DVD)
Both use a single, spiral track which runs from the centre of the disk to the edge.
When a disk spins, the optical head moves to the point where the laser beam ‘contacts’ the disk surface and follows the spiral track from the centre outwards.
more about how they work
As with a HDD, a CD/DVD is divided into sectors allowing direct access to data. Also, as in the case of HDD, the outer part of the disk runs faster than the inner part of the disk.
how is the data stored and how is it read?
The data is stored in ‘pits’ and ‘lands’ on the spiral track. A red last used to read and write the data. CDs and DVDs can be designated (write once only) or ‘RW’ (can be written to or read from many times)
how is the data stored and how is it read?
The data is stored in ‘pits’ and ‘lands’ on the spiral track. A red last used to read and write the data. CDs and DVDs can be designated (write once only) or ‘RW’ (can be written to or read from many times)
DVD technology?
DVD technology is slightly different to that used in CDs.
main differences = the potential for dual-layering, which increases the storage capacity. this means that there are two individual recording layers.
Two layers of a standard DVD are joined together with a transparent spacer, and a very thin reflector is also sandwiched between the two layers.
Reading and writing of the second layer is done by a red laser focusing at a fraction of a millimetre difference compared to the first layer
comparison of DVD and Blu ray
A standard dual-layer DVD has a storage capacity of 4.7 GB (enough to store a 2-hour standard definition movie)
- A single-layer Blu-ray disc has a storage capacity of 27 GB (enough to store a 2-hour high definition movie or 13 hours of standard definition movies)
- A dual-layer Blu-ray disc has a storage capacity of 50 GB (enough to store4.5 hours of high definition movies or 20 hours of standard definition movies).
