A storage device is a piece of electronic hardware made to store data. Some storage devices have storage as their only function, while others are actually multifunction devices, which may store data as well as perform other roles. Storage devices are divided into primary storage devices and secondary storage devices, but there are two different ways to consider which devices are primary and which are secondary. In one view, while current data are stored in primary storage devices, data that is not currently being accessed are stored in secondary storage devices, with all of those devices being on the computer. In the second view, all storage devices that are part of the computer are primary storage devices, while any storage that is peripheral is what is referred to as secondary storage devices.
According to the first view, the primary storage device is the computer’s random access memory (RAM). RAM holds data that is immediately available to the CPU (Central Processing Unit) to which it is directly connected. The data in RAM is data that has been loaded by the operating system and active programs, and it requires electrical current to be maintained there.
The computer’s hard drive, on the other hand, is secondary storage in this view because it is not directly connected to the CPU. Since it stores data magnetically, the data on the hard drive will persist after the computer is turned off, while data in RAM will be lost once the computer is turned off, since the electrical current will no longer be available.
In the second view, in which the primary storage devices include all the computer’s original data storage — both RAM and hard drives — secondary storage devices can be an array of other types of storage and media that are external. This type of secondary storage device may include add-on internal drives, external hard drives, floppy disks, tape storage, and thumb drives. As far as the optical drives go, secondary storage devices could include CDs and DVDs, as well as other optical media. Since the computer’s internal hard drive can either be considered a primary storage device or a secondary storage device, depending on which view is embraced, it is important to be clear when discussing primary and secondary storage devices in order not to be misunderstood.