Whilst Main Memory is used to run the system, a computer also needs places to store programs and data for longer. The term used to describe these types of media is secondary storage.
Whilst secondary storage is used to store data whilst the power is switched off, it is also used to hold data and programs that are not currently in use. Once the system needs to use these, they are moved into the RAM.
The computer hard drive may also be used for virtual memory if the RAM runs out of space.
Secondary storage is placed into three main catagories: Magnetic, Optical, and Solid State.
Magnetic storage uses a magetic charge to store binary on the media. This can then be read with positive indicating a one, and negative indicating a zero.
Hard disk drives (HDD), floppy disks, and magnetic tape are all examples of magnetic storage.
Optical media can roughly be descibed as “anything that is read using a laser“. These are usually types of disck.
CDs, DVDs, and Blu-Ray are all examples of types of optical storage.
Solid state devices come in a number of formats, with many being built on flash memory technology. Solid state media has no moving parts, and as such is less prone to damage whilst being moved about. It is for this reason that solid state storage is used in so many portable devices.
SSDs, USB sticks, and SD cards are all examples of solid state storage.
To read more about the types & characteristics of secondary storage, click here.