Difference between Internal and External Fragmentation

Internal Fragmentation

In fixed partitioning, the various partitions can be of same size or different size.
Whenever a new process arrives & needs memory, it is allocated a partition large enough to hold the process.
However, the size of partition may be larger than the size of the process. In such a case part of memory partition goes waste and remains unused. Such as unused space is called fragment.
Thus, the allocation of a process to a partition greater than the process’s requirement results in the wastage of space internal to a partition. This is known as internal fragmentation.

It is called internal fragmentation because the memory is wasted within the space allocated to process i.e. internal to a partition.
For Example, The memory consists of three partitions of size 200k, 300k and 400k respectively. These partitions are occupied by 3 processes A, B and C of size 150k, 200k and 300k respectively. The allocation of these 3 processes to the partitions results in the wastages of 50k, 100k and 100k in partitions 1, 2 and 3 respectively.

In variable partition allocation, each process is allocated exactly the same amount of memory it requires.
In such a way processes after finishing their execution leave the memory and some new processes are loaded in the same space.

As the memory requirement of different processes is not same, the swapping of different processes results in the formation of unusable memory holes. This is known as external fragmentation.
It is called external fragmentation as the memory space is wasted external to the allocated memory partitions.

Internal Fragmentation	External Fragmentation
It is the wastages of memory space that is within (inside) the partition allocated to a process.	It is the wastage of memory space that is outside the partitions allocated to processes.
It occurs when process is allocated partition greater than its requirement.	Such a fragmentation occurs when process is allocated exactly the same memory space as it requires.
This type of fragmentation occurs when we implement multiple fixed partition method and paging.	This type of fragmentation occurs in multiple variable partition method and segmentation.
Internal fragmentation results in the duction of number of frame that are available.	External fragmentation results in the reduction of amount of usable memory.
Diagrammatically internal fragmentation is represented as:	Diagrammatically external fragmentation is represented as: