Secondary Storage

Non-Volatile, Data is not lost when there is no power

Storing a backup copy of data, so that if lost data can be restored

• Consists of metal disks which are coated with a magnetic material • The disks are divided into tracks which are divided into sectors • The disks rotate very quickly • Read/write heads move across the disk surface to access or store data on the disk

Because the data is stored in magnetic material

• They have a high data transfer rate - Highest storage capacity

• Not very portable, care has to be taken handling them - Access times are slower than SSD’s because they have moving parts

• Has a plastic disk with a mirrored surface • Data is burned or pressed onto the surface of the disk • This creates a series of Pits and Lands • The pits has a value of zero, the lands have a value of one • Laser beams are used to read the data on the disk since the pits and lands reflect different amounts of light, which are decoded into the original binary data. • The reader starts reading data on the inside of the disk and works its way to the outside.

• CD - 650 Mb • DVD - 4.7 Gb • Blu-ray - 25 Gb

• Very portable - Cheap to produce

• Can be easily damaged • less storage capacity than a hard disk drive • Slower access time that Hard Disks and Solid state drives

• comprised of NAND flash memory cells arranged in a grid • has a controller that manages pages/blocks of memory • data is stored using floating gate transistors • The transistors can trap and store charge • data must be read in pages and written/erased in blocks

• They can read, write and access data faster that Hard drives as they have no moving parts • They are more durable than optical storage/HDD’s

• More expensive to buy than Hard Disk Drives - Tend to be of smaller capacity that Hard Disk Drives

• By adding more platters - By decreasing the track width