Difference Between Static and Dynamic Memory Allocation

Static and Dynamic memory allocation are the two ways in which memory allocation is classified. The significant difference between static and dynamic memory allocation is that static memory allocation is the technique of allocating the memory permanently. Thus, it is fixed memory allocation. As against, dynamic memory allocation is the way of allocating memory according to the requirement and hence is variable memory allocation.

There are some parameters on which the two are differentiated but before that, we must know –

What is memory allocation?

Memory allocation is defined as the way of allotting memory space to one or more processes. Through memory allocation physical or virtual memory space is assigned to programs or processes.

By memory allocation, complete or partial computer memory is reserved for programs and processes. The memory allocation is mainly classified as Static and Dynamic memory allocation. Memory allocation is a hardware operation but operating system and software applications are responsible for managing it.

It is to be noted here that before program execution, the determination of accurate program memory required to run the program is quite difficult. Thus, most of the time the memory allocation decisions are made at run time.

Content: Static Vs Dynamic Memory Allocation

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

Comparison chart

Basis for ComparisonStatic Memory AllocationDynamic Memory Allocation
Abbreviated asSMADMA
BasicFixed type of memory allocation.Variable type of memory allocation.
OccursBefore program executionDuring program execution
Space required More Comparatively less
Memory reusabilityNot existExist
Execution speedFast Comparatively slow
Fragmentation issueNot existExist
Memory sizeUnchangeableChangeable
Used in ArrayLinked list
SuitsWhen there is an advance idea about memory size.When there is no idea about exact memory size.
Implemented Through stackThrough heap

Definition of Static Memory Allocation

SMA, an acronym for static memory allocation is a way by which fixed memory space is assigned to a program before program execution. It is also known as fixed memory allocation as in this approach once a memory space is assigned then no further changes can take place regarding space adjustments or reassigning.

SMA offers pre-reserving the memory space and the data structure stack is used for its implementation.

In static memory allocation, once a memory space is assigned to a process then it does not matter whether the program is using that memory at that particular instant or not. Because that allocated memory cannot be used for any other purpose. This means that even if the memory is of no use, then also under static memory allocation technique the assigned memory cannot be reused.

The static memory allocation mainly shows suitability towards memory management of short memory spaces where the required memory size is already known before assigning.

Definition of Dynamic Memory Allocation

DMA, an acronym for dynamic memory allocation is a way of assigning memory space to a process or program at the time when program execution takes place. It is sometimes referred to as the variable or manual memory allocation as it permits reassigning or adjustability in the assigned memory space when the memory is not used by the respective  process.

This technique does not allow pre-reserving of memory space before program execution and heap data structure is used for its implementation. Through DMA, assigning and releasing of memory can occur at any time.

Unlike SMA, here reallocation and even freeing of used memory space is permitted. Here functions like calloc(), realloc(), and free() are used for assigning, reassigning, and freeing memory space within a system. Dynamic memory allocation manages available memory space efficiently. However, one of the major drawbacks of this is memory leakage. Memory leakage arises when some programs continuously use memory space but do not free the spaces which are not in use then after a point of time, the system runs out of memory.

Key Differences Between Static and Dynamic Memory Allocation

  1. The key factor of differentiation between static and dynamic memory allocation is that static memory allocation is a fixed type of memory allocation where the memory space assigned is fixed. On the contrary, dynamic memory allocation is a variable type of memory allocation where the assigned memory space varies according to the requirement.
  2. As static memory allocation pre-assigns a fixed memory space thus chances of wastage of memory space when unused are high. As against, through dynamic memory allocation, memory space required can be increased or decreased according to requirement thus, chances of memory space wastage are quite low.
  3. SMA does not offer memory reusability due to its fixed nature but memory can be reused when assigned under DMA.
  4. SMA is suitable for all those conditions where there is an advance idea regarding the size of memory size required. But DMA is suitable for conditions where the exact memory size required is not known in advance.
  5. Static memory allocation is a comparatively faster way of assigning memory space than dynamic memory allocation. The reason for this is that assigning a fixed amount of memory is less time-consuming than variably assigning the same.
  6. SMA is comparatively less efficient than DMA as the former offers drawbacks such as memory wastage and non-reusability. While DMA overcomes these drawbacks hence is more efficient.
  7. When memory space gets permanently assigned to a program then fragmentation issue does not occur. But when there is variability in assigning the space then even the available memory space if present in fragments is of no use.
  8. Static memory allocation requires more memory space than dynamic memory allocation.


Thus, it is said that the implementation of static memory allocation is quite simpler in comparison to dynamic memory allocation.

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