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Difference between Internal Fragmentation and External Fragmentation

Difference between Internal Fragmentation and External Fragmentation

Disk fragmentation is a term used to describe the condition of a disk drive when it becomes cluttered with files that have been split into fragments. When a disk is fragmented, the system takes longer to access and open files because the drive has to search for each fragment of the file separately. In this blog post, we’ll take a look at the difference between internal fragmentation and external fragmentation, and explain how you can use both techniques to keep your disk drives running smoothly.

What is Internal Fragmentation?

Internal fragmentation is the wasted space that results from using a fixed-size block allocation algorithm on a file system. When a file is created, it is stored in a free block. If the file is too large to fit in a single block, additional blocks are allocated. However, if the file is small, there will be unused space in the block.

  • Over time, this wasted space can add up, leading to Internal Fragmentation. Internal Fragmentation can also occur when blocks are pre-allocated for a file but not all of the blocks are used. While Internal Fragmentation is not usually a major issue, it can lead to decreased performance and increased storage costs.
  • Internal fragmentation is one of several types of fragmentation that can occur in a file system. Other types of fragmentation include External Fragmentation and File Fragmentation. Internal fragmentation is often caused by files that are frequently modified or deleted. When a file is modified, it may no longer fit in the same block.
  • As a result, the file may need to be stored in multiple blocks, leading to internal fragmentation. File deletion can also cause internal fragmentation if the blocks that were allocated to the file are not immediately reclaimed by the file system. Internal fragmentation can be minimized by using variable-sized blocks or by carefully choosing the size of each file in advance. Internal fragmentation will always occur to some degree on any file system; however, by minimizing it, we can improve performance and reduce storage costs.

What is External Fragmentation?

External fragmentation occurs when free space is not contiguous. This can happen, for example, when blocks of free space are scattered throughout memory. External fragmentation can lead to memory-related problems because it can make it difficult for a program to find a large enough block of contiguous free space to store data.

External fragmentation can be minimized by using an allocation algorithm that tries to keep blocks of free space together. For example, buddy allocation is a common technique for managing memory that can help to reduce external fragmentation.

Difference between Internal Fragmentation and External Fragmentation

Internal and external fragmentation are two types of memory fragmentation. Internal fragmentation happens when there is wasted space inside an allocated memory block.

  • This happens because the operating system can only allocate memory in certain sizes (e.g., 4kb, 8kb, 16kb, etc.). So, if you have a piece of data that is only 1kb, the operating system will still allocate 4kb for that data.
  • The other 3kb is wasted space and is considered Internal Fragmentation. External Fragmentation happens when there are multiple small pieces of free memory scattered around.
  • When the operating system needs to allocate memory for a new process, it first needs to find a large enough contiguous block of free memory. If there are multiple small pieces of free memory scattered around, it can be difficult to find a large enough contiguous block of free memory.

External Fragmentation can lead to Internal Fragmentation because the operating system may need to use multiple smaller blocks of free memory to allocate one large block of contiguous memory. Internal and External Fragmentation can both negatively impact performance because they can lead to wasted space in memory.


Internal fragmentation can lead to system instability and data loss, while external fragmentation does not have the same risks. Understanding the difference between internal and external fragmentation is important for anyone who wants to maintain a stable and efficient system.

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