Permanent storage, also called persistent storage, is any computer data storage device that retains its data when the device is unpowered. A common example of permanent storage is the computer's hard drive or SSD.
Examples of permanent storage devices
- Blu-Ray disc
- CD-ROM disc
- CD-R and CD-RW disc
- DVD-R, DVD+R, DVD-RW, and DVD+RW disc
- Floppy diskette
- Hard drive
- Jump drive or flash drive
- Memory card
- Memory stick
In comparison to permanent storage, non-permanent storage, also called volatile memory, is a storage device whose data is lost when its power source is disconnected. Examples of non-permanent storage include CPU cache and RAM.
How they work together
Permanent and non-permanent storage devices have advantages and disadvantages that complement each other. They work well in conjunction with one another, because each does something well that the other does not.
Non-permanent storage operates faster than persistent storage (its data is accessed at a lower latency). However, it is more expensive to manufacture. Therefore it is manufactured in smaller capacities, and the computer uses it as a scarce resource for the most time-critical applications.
Permanent storage operates more slowly than non-permanent storage, but is cheaper to manufacture. Its primary use is long-term data storage, for things like your operating system, applications, and documents. When you use a specific application, that data is loaded into RAM (non-permanent storage), where it operates much more quickly.
Generally speaking, the slower storage is, the larger its capacity. For instance, a computer may have a 2 TB hard drive and a 256 GB SSD for permanent storage. The same computer may use 16 GB of RAM, and 9M of CPU cache, as volatile storage. The slowest, cheapest storage (the hard drive) has the largest capacity, and the fastest, more expensive storage (CPU cache) is the smallest.