The differences between internal & external fragmentation

Written by carol finch Google
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The differences between internal & external fragmentation
Internal and external fragmentation can slow down a computer (Comstock/Comstock/Getty Images)

Fragmentation occurs in computer storage when memory space is not used efficiently. As a computer is used over time, files, software programs and automatic space allocation affect the way that available memory is organised and it moves from a contiguous to a fragmented state. There are two main types of fragmentation: internal and external. What are the differences?

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All computers come with a memory capacity. This space is used by the computer and its user to store data and operate software programs. For example, when a program tells a computer that it needs a certain amount of memory to work, the computer will allocate the number of blocks of memory it needs. These are then released when the program is closed down. A similar process occurs when files and data are saved, deleted and moved by the user. Over time, however, memory allocations can change in size and position and will become fragmented. This turns a large block of memory into smaller and less efficient ones and can cause capacity and performance problems.

Internal fragmentation

Computers allocate memory in bytes according to certain rules. One of these dictates that memory must be allocated to a predetermined block size. If a software program needs more than one block, for example, it will be allocated two. It may not need all the memory it is given, but the blocks will be ring-fenced for it. This extra memory, known as slack space, is not usable while the program runs even though it is theoretically free. This process is known as internal fragmentation.

External fragmentation

External fragmentation most often occurs when a user saves files. The computer will allocate an amount of memory for each file. If a file is deleted or moved to another location, that memory will be freed up again. If, however, the computer saves another file to that space and it is smaller than the original, the excess memory will be left over in its position. It may then become unusable if it is too small for any future file or document even though it is free to use. Problems can also occur if you amend files as changes can be stored in a different location to the original. This can cause a loss of operating speed as the computer needs to search in different places to bring the components of a file together.

How to manage internal and external fragmentation

There are ways to manage internal fragmentation problems, but these require in-depth computing knowledge and users may not feel confident taking this job on. It is easier to control external fragmentation. Defragmentation tools can analyse a system's memory, assess how it is organised and then rearrange it to make it work more efficiently.

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