For any orderly system, storage units are those that allow physical or virtual storage of data files of all kinds.
More specifically in computing, the storage units will be all those devices, internal or external, that store the information of a given system. The devices will differ from one another in shape, size, and use, but collectively they all contribute to the preservation of user-relevant data in digital form.
There are multiple storage units available. The most common of these is HDD, that unit that is included in most computers and that, among other things, stores the information that allows the system and programs to be started, as well as text files, images, audio and video of the user. The hard drive comes in a variety of sizes and is often expandable. Unlike other drives, this one often has a higher capacity measurable in gigabytes (GB), a higher spin speed, that is, access to information, and a better data transmission capacity. Hard drives are typically internal, but can be purchased as external drives that store large amounts of information and can be easily transported from one system to another, for example, to exchange data between two computers.
Other popular storage units are CD-ROMs or DVD-ROMs, which are usually much smaller than a hard drive but provide the alternative of storing smaller amounts of information with much more flexible mobility. However, in most CDs and DVDs information can only be written once, and then this data can neither be erased nor supplemented by others.
More recently, the flash drives or USB, small storage devices of variable size that keep the information inside and that may or may not require batteries. It connects to a computer via a USB port and allows easy transport of large amounts of information from one system to another.
