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In computer storage, secondary storage, or external memory, is computer memory that is not directly accessible to the central processing unit of a computer, requiring the use of computer's input/output channels. Secondary storage is used to store data that is not in active use. Secondary storage is usually slower than primary storage, or internal memory, but also almost always has higher storage capacity and is non-volatile, which makes it perfect for the preservation of stored information in an event of power loss.

Storage devices in this category include:

• CD, CD-R, CD-RW
• DVD
• Flash memory
• Floppy disk
• Hard disk
• Magnetic tape
• Paper tape
• Punch card
• RAM disk
• External Hard Drive