Difference Between Primary and Secondary Memory

The two major types in which memory is classified are primary memory and secondary memory. The crucial difference between primary and secondary memory is that primary memory is the core memory of the computer system where data and information are stored. As against, secondary memory is the auxiliary memory that is used for storing data and information.

Primary memory is basically internal memory that resides within the processor unit while secondary memory is not a part of the processor and exists as an external additional unit.

What is Memory?

Memory is regarded as a unit or device within which data or instructions are stored either temporarily or permanently. The basis of data storage depends upon the type of memory. The content of memory exists in binary format i.e., in 0s and 1s. The processor while operating accesses the data from the memory and performs the necessary operations.

Content: Primary Vs Secondary Memory

  1. Comparison Chart
  2. Definition
  3. Key Differences
  4. Conclusion

Comparison chart

Basis for ComparisonPrimary MemorySecondary Memory
Also calledInternal MemoryBackup or auxiliary memory
Storage typeTemporaryPermanent
Storage sizeSmallLarge
CostMoreComparatively less
AccessibilityDirectly by the processor.Not directly by the processor.
Data storedActual data which is under operation.A huge amount of data required for operation.
Accessing speedFast Comparatively slow
NatureVolatile as well as non-volatileNon-volatile
Accessed viaData busInput output channels
Data transferabilityNot possiblePossible
Memory typeSemiconductor memoryMagnetic or optical memory
ExamplesRAM, ROM, cache, registers, etc.Hard disk, floppy disk, magnetic tapes, etc.

Definition of Primary Memory

Primary memory is the internal memory of a computer system that stores data and information on a temporary basis. These are basically present in the form of semiconductor chips within the computer systems and so offer less space for storing dataand the processor can easily access the content within it therefore the data within it gets accessed at a faster rate.

The semiconductor chips that act as primary memory are located on the motherboard thereby offering quick access.

The classification of primary memory is such that

types of primary memory

The difference between RAM and ROM i.e., the two major classifications of main memory is that the data within ROM cannot be altered as it can only be read. ROM is further classified as:

  • MROM
  • PROM

While the RAM offers temporary storage to the data and the data must necessarily exist in RAM in order to get executed by the processor. The RAM is classified as:

  • DRAM
  • SRAM

Definition of Secondary Memory

Secondary memory is the backup memory of a computer system that stores a huge amount of data on a permanent basis. It is used for mass storage of data in a range of gigabytes to terabytes. It acts as external storage whose data cannot be accessed by the processor directly during the operation however, according to the requirement the data from the secondary memory gets loaded into the primary memory in order for the operation to take place.

This makes the accessing of this memory in reference to the processor quite slow. Also, there exists non-uniformity in storing the data within the secondary memory. But the content residing within the secondary memory can be easily transferred from one physical device to the other.

The various secondary memories are as follows:

  • Hard disk
  • Compact disk
  • Pendrive
  • SD card
  • Solid-state drive
  • DVD

These memories retain data within it even after electrical power failure.

Key Differences Between Primary and Secondary Memory

  1. The key factor of differentiation between primary and secondary memory is based on the longevity of the presence of data or information within the memory. Basically, primary memory is considered to be the internal memory of the system and so holds the data and information related to any ongoing operation which is taking place inside the system. As against, the secondary memory is not considered as a memory that is part of the system but it holds the data which is required for upcoming operations in an external location.
  2. The data within primary memory generally possess volatility and so lasts only till the time the device is connected to the power supply. While the data within secondary memory is held in a non-volatile manner that means resides even after power failure and is used according to the need.
  3. As the primary memory is regarded as the main memory of the system due to its presence within the system itself thus the data within it can be directly accessed by the processor. However, the secondary memory is known to be the auxiliary memory as it does not exist within the system rather is an external unit similar to input-output devices therefore the data within it cannot be directly used by the processor for operation.
  4. The size of the storage offered by the primary memory is around 32 to 500 GB while that of the secondary storage is around 200 GB to terabytes. This means that the size of the primary storage is comparatively smaller than the secondary storage.
  5. The main memory possesses inbuilt nature thus is comparatively costlier than auxiliary memory.
  6. The storage type offered by primary memory is temporary in nature as it stores data only for the time being when the system is powered and once power failure occurs then the data stored will get lost. As against, secondary memory stores data permanently as in this case data is not lost even if a power failure occurs.
  7. As the data in the primary memory is directly accessed by the CPU for the operation, therefore, the accessing speed is faster in comparison to that of secondary memory whose data the processor cannot use directly at the time of operation.
  8. Primary memory is a type of semiconductor memory that is formed using semiconductor materials whereas secondary memory is regarded as magnetic or optical memory which uses the magnetized medium for storing the data.
  9. As primary memory is itself a part of computer architecture thus data bus is used to access the content present within it. While the secondary memory is considered as a separate unit similar to other input-output units thus its data is accessed by I/O channels.
  10. The data stored within the main memory of a system cannot be transferred to another system until and unless it gets permanently stored. While the data existing in the secondary memory of a device can be easily transferred to another device.


Thus from this discussion, we can conclude that the primary memory simply holds the data which is currently in use by the processor in order to support ongoing applications. But secondary memory is somewhat different because it has a huge space that contains a large number of data that is transferred to the main memory when required to be used by the processor.

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