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Primary storage device

Primary storage device

(also main memory, primary memory)

Primary storage device definition

A primary storage device is a type of data storage that is actively used or processed by the computer’s central processing unit (CPU). The data in primary storage is typically volatile — it’s lost when the system is powered off.

CPU directly accesses primary storage and uses it for active processing. In contrast, secondary storage devices, like hard drives, SSDs, CDs, and USB drives, store data for long-term retention and are not directly accessed by the CPU.

See also: direct memory access, CPU utilization

Examples of primary storage devices

Primary storage device

  • The most common type of primary storage.
  • It provides the space for the computer to read and write data to be accessed by the CPU.
  • Modern computers typically use DRAM (Dynamic Random Access Memory) as their main RAM, though SRAM (Static Random Access Memory) is faster and more reliable but also more expensive.

Cache Memory

  • A smaller type of volatile computer memory that provides high-speed data access to the processor and stores frequently used computer programs, applications, and data.
  • Provides faster data storage and access by storing instances of programs and data routinely accessed by the processor.


  • The smallest and fastest type of primary storage.
  • Hold instructions and data that the CPU is currently processing. They are integrated directly into the CPU itself.

ROM (Read-only memory)

  • Not used for active processing.
  • Retains its contents even when the computer is turned off, making it non-volatile.
  • It typically contains the firmware — software that’s permanently programmed into the computer. ROM usually stores the computer’s BIOS.

Further reading

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