Classification Based on Storage Medium

Storage system

There are multiple storage options available, which differ in speed, cost, and accessibility.

• Primary storage holds the currently running instructions and data on the motherboard. Hence, access to the primary storage is always faster. However, primary storage is volatile and can lose its contents after system restarts. Also, storage size is limited and expensive. Primary storage includes the main memory and cache as part of its hardware.

• Secondary storage devices (e.g. magnetic disks) are nonvolatile devices outside the CPU that hold data and programs for longer periods of time. The data stored on secondary devices persists on system restarts. Secondary devices are economical and can store large amounts of data, but the access patterns are comparatively slower than the primary storage. These are also called online storage.

• Tertiary storage devices (e.g. tapes and optical disks) are nonvolatile devices that can hold large amounts of data outside to the computer system. They are also called offline storage and are the slowest of the storage systems.

The costs and access speeds progressively decline from primary storage to tertiary storage, while the data retention capacity increases from primary storage to tertiary storage.