External Fragmentation

Definition

External fragmentation refers to the condition in a computer's memory allocation system where free memory is split into small, non-contiguous blocks, making it difficult to allocate larger contiguous blocks when needed. This phenomenon occurs when processes are loaded and removed from memory, leaving behind small gaps of free space that are too small for subsequent processes, ultimately leading to inefficient memory usage. It's important to understand how this affects various memory management techniques, file storage, and free space management.

5 Must Know Facts For Your Next Test

1. External fragmentation can lead to significant waste of memory resources as available free space is scattered throughout the memory.
2. It often results from dynamic memory allocation techniques where processes vary in size and are loaded and unloaded at different times.
3. The degree of external fragmentation increases as more processes are added and removed, leading to smaller and smaller gaps in memory.
4. This type of fragmentation does not affect the overall size of memory but makes it less efficient for allocation purposes.
5. Various strategies like paging and segmentation are implemented in modern operating systems to mitigate the impact of external fragmentation.

Review Questions

• How does external fragmentation impact memory allocation techniques in operating systems?
  • External fragmentation significantly affects memory allocation techniques by creating small, unusable gaps between allocated blocks of memory. When a system tries to allocate new processes, it may find that there isn't enough contiguous space available, despite having enough total free memory. This leads to inefficient memory usage and can force the operating system to either deny requests for new allocations or use complex algorithms to manage these fragmented spaces.
• Discuss the relationship between external fragmentation and file allocation methods in operating systems.
  • External fragmentation relates closely to file allocation methods as it can affect how files are stored on disk. When files are created, modified, or deleted, the storage space can become fragmented, making it difficult for the system to find contiguous space for new files. This can lead to slower read/write times and increased overhead for the file system as it must manage these scattered pieces rather than accessing data in larger contiguous chunks. Efficient file allocation methods aim to minimize this fragmentation.
• Evaluate the effectiveness of strategies like compaction in reducing external fragmentation and their potential downsides.
  • Compaction can be an effective strategy for reducing external fragmentation by consolidating free spaces into larger contiguous blocks. However, it comes with downsides such as the need for considerable processing time and potential disruption of active processes. During compaction, the system may need to pause other operations, leading to performance degradation. Additionally, frequent compaction could result in increased overhead due to constant movement of data within memory.

Related terms

Internal Fragmentation: Internal fragmentation occurs when memory blocks are allocated to processes but not fully utilized, resulting in wasted space within allocated regions.

Paging: A memory management scheme that eliminates external fragmentation by dividing physical memory into fixed-size pages and mapping them to logical addresses.

Compaction: A process of rearranging the memory contents to combine free spaces into larger contiguous blocks, thus addressing external fragmentation.