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What are primary and secondary storage devices?

Answer: A computer stores data using several different methods. Therefore, there are different levels of data storage, which may may be referred to as primary and secondary storage. A computer's internal hard drive is often considered a primary storage device, while external hard drives and other external media are considered secondary storage devices.

However, primary and secondary storage may also refer specifically to the components inside the computer. In this case, primary storage typically refers to random access memory (RAM), while secondary storage refers to the computer's internal hard drive.

RAM, commonly called "memory," is considered primary storage, since it stores data that is directly accessible by the computer's CPU. RAM is a high-speed storage medium that can be accessed with minimal delay. Because the RAM is connected directly to the CPU via the memory bus, the CPU can access data stored in RAM very quickly. For this reason, RAM is used to store data loaded by active programs and the operating system.

Hard drives are considered secondary storage since they are not connected directly to the CPU. Instead, hard drives send and receive data through an I/O bus, which may pass through a cache or other type of memory before getting to the CPU. Also, hard drives are not as fast a RAM, which means they cannot transfer data as quickly. However, unlike RAM, hard drives retain data when the computer is turned off. This is because hard drives store data magnetically, while RAM requires an electrical current.

While the computer's primary internal hard drive is the most common secondary storage device, other devices may be considered secondary storage devices as well. These include additional internal hard drives, external hard drives, and optical drives, which are used for CDs, DVDs, and other optical media.

Published: August 7, 2009 — by Per Christensson

Answer from the PC Help Center