Drive: the device that reads and writes data from secondary storage

Media: what the data is actually stored on

• solid state storage, such as USB memory sticks

• optical storage, such as CD, DVD and Blu-ray discs

• magnetic storage, such as hard disk drives

Secondary and off-line storage includes storage devices that are not directly addressable by the CPU. They are non-volatile devices that allow data to be stored as long as required by the user. This type of storage can store more data than primary memory but data access time is longer than with RAM or ROM. 

All applications, the OS, device drivers and general files are stored on secondary storage. 

In the case of optical storage, we have an optical drive and a choice of media which includes:

• Compact disk read only - CD-R

• Compact disk read-write - CD-RW

• Digital versatile disc read only - DVD-R

• Digital versatile disc read-write - DVD-RW

• Blu-ray

Optical Storage: Taken from Google Slides

The read only media became common to be able to distribute music, films and games as the content can only be read and not changed. This type of storage can be written to once and read many times. Whereas the read/write media can be read and written to many times making them more commonly used for backup options. Blu-ray which was designed to take over from DVD has the greatest storage capacity to date.

All Optical drives work by shining a laser at the media and processing the reflection from the media. In the case of read only drives, the surface of the disk is physically burnt by the laser creating pits and lands which are suitable for storing binary 0’s and 1’s. 

When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam, a sensor looks for the reflected light. Once the surface has been burnt it can not be changed making the media read only. In the read / write option the disk can be written to more than once because the chemical composition of the disk has been changed by a reversible chemical reaction.

Magnetic Taken for Google Slides : 

Hard disks are still one of the most common methods used to store data on a computer. They use magnetic fields to magnetise tiny individual sections of a metal spinning disk which spins about 7000 times a second. Each tiny section represents one bit. 

Read write heads consist of electromagnets that are used to read data from or write data to the platters. A magnetised section represents a binary one and a demagnetised section represents a binary zero. Magnetic devices are fairly cheap, high in capacity and durable. However, they are susceptible to damage if dropped, due to the moving parts and they are also vulnerable to magnetic fields. The drive head makes it a bit slower compared to drives with no moving parts and because it has mechanical parts it will eventually fail.

Solid state : Taken from Google Drives : 

Hard disks are still one of the most common methods used to store data on a computer. They use magnetic fields to magnetise tiny individual sections of a metal spinning disk which spins about 7000 times a second. Each tiny section represents one bit. 

Read write heads consist of electromagnets that are used to read data from or write data to the platters. A magnetised section represents a binary one and a demagnetised section represents a binary zero. Magnetic devices are fairly cheap, high in capacity and durable. However, they are susceptible to damage if dropped, due to the moving parts and they are also vulnerable to magnetic fields. The drive head makes it a bit slower compared to drives with no moving parts and because it has mechanical parts it will eventually fail.

Solid state drives work by a flow of electricity forcing electrons into floating gates between two oxide layers. This causes a change in the charge in the floating gate and this can be measured as a zero or a one. 

Over time the oxide layers deteriorate meaning the transfer of electrons becomes unreliable. This means that ss media has a limited number of read-write cycles and therefore a limited life span.