Having one layer for user data and a second layer for back-up copies of the same data

Using two different colours of laser to increase data transfer speed

Joining two recording layers with a transparent spacer so data can be read from a first and a second layer

Storing data on both sides of the same physical disk

The tiny depressions and raised areas on the spiral track that represent digital data

Areas of the disk reserved for error-correction codes

Physical defects on low-quality disks that cause read errors

Sections of the disk used only for storing system files

Flash memory can only be read, while EEPROM can only be written

EEPROM can read or erase individual bytes, while NAND flash reads or erases blocks of data

NAND flash is volatile, while EEPROM is non-volatile

EEPROM stores data using magnetic properties, while NAND flash uses electrical charges

The number of times the SSD can be powered on and off before it fails

The speed at which the SSD can read large continuous blocks of data

The length of time data can be stored on the SSD without power

The maximum number of write operations the device is rated for over a given period

Encrypt data on each sector so it becomes more secure

Compress files so that they occupy fewer sectors on the disk

Rearrange sectors so that files are stored in adjacent blocks, improving access time

Duplicate frequently used files on multiple platters to increase reliability

The time taken for the read–write heads to move from the centre of the disk to the edge

The time it takes for a specific block of data on a track to rotate round to the read–write head

The time required to spin the platters up to their maximum speed

The delay caused when data is transferred from primary memory to secondary storage