Basically, a storage unit is a device able to read and write data for the purpose of permanent storage. Today we have available many classes and categories of this storage devices, and can find in computer stores a wide variety, both internals and externals, capable of storing an amount of data unthinkable in the past.
Also called secondary storage, these devices are capable of storing data inside, as in the case of hard drives, memory cards and USB flash drives, or as in the case of optical storage drives such as Blu-Ray, DVD or CD disc, which store data externally on a removable media, such as disk.
This type of device is the safest and most convenient way to store a significant amount of information easily and permanently. Notably thus we can also maintain the data always available, since such media do not need power to maintain the stored information.
The ability to store information for later retrieval simple is an essential link in any modern computer system, and the storage devices play a major role in the development of technology, because without them it would be impossible even attempting any project, however small it may be.
Types of storage devices
Currently there are three types of devices we use in everyday tasks to store and move information
Optical: CDs, DVDs, Blu-Ray, etc.
Magnetic and mechanical: Hard disks, magnetic tapes, diskettes, etc.
Electronic (no mechanics parts inside): SSD, flash drives, memory cards, etc.
Storage memory and RAM
One of the mistakes that most often incurred by computer users is to confuse the RAM of the PC with a storage device, but this is not true because the RAM only stores data temporarily, for the purpose that these data are processed by the CPU. The data in the RAM is never stored permanently.