The term data storage can refer to anything with information recorded on it. Using this broad definition, a hardback volume of an encyclopedia, an audio cassette of a pop song, and even a piece of paper with random words written on it would all be considered examples. The most popular definition of the term limits it to only the storage of information on computers and similar devices.
Everything a computer “knows” or is able to “know” is called computer data. This includes e-mails, text files, digital pictures, and databases. Computer data storage can be divided into two main categories: primary and secondary. Each is important, but the secondary type is usually what people think of when they use the term.
The information that a computer has at any given time is technically what data its central processing unit (CPU) can directly access. This information is called memory, and the components that store it are considered primary storage. Memory is mainly stored on Random Access Memory (RAM). There are many types of RAM, but they usually come in the form of modules that plug into a specific slot inside the computer. This type is constantly being erased and rewritten, most often from secondary storage.
Secondary data storage represents all of the other types not included in the primary storage. Though some experts previous used an additional category called tertiary, technological advances have blurred the differences between the secondary and tertiary levels to the point that only one term is necessary. Internal hard disk drives, CD-ROM disks, and flash memory sticks are all examples of this type of storage. There are so many different types that this category can be further divided into three different areas: on-site, removable, and off-site.
On-site storage represents any type of storage device that is designed to remain with the computer or at a single location where the computer is housed. The most common on-site device is a hard disk drive, and it is included in almost every personal computer. Solid state drives and network attached storage are also examples of such devices.
Removable memory is any type that is designed to be easily removed from a computer. This type has become more common than on-site types in modern times. The big disadvantage of this type used to be that data access time was much slower than on-site, but speed improvements have decreased this to within acceptable limits for many common applications. CD-ROMs, DVD-ROMs, USB flash drives, and portable hard disk drives are all examples.
Off-site data storage is one of the most recent types of storage. In this type, information is stored away from the computer at a distant location. This data can then be accessed either by a direct call or through the Internet. This type of storage has the advantage of being available if something happens to the on-site computer system.
There are disadvantages to off-site storage compared to other types, both because of how long it takes to access the data and because it can be less secure. Examples of this type include electronic vaulting, on-line file hosting services, and on-line photo sharing websites. It is also a primary aspect of cloud computing.