What is External Fragmentation In OS ?

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External fragmentation is a situation that arises in operating systems due to dynamic memory allocation. It occurs when there's enough total free memory available to fulfill a memory request for a process, but the available free memory is scattered across the memory in chunks that are too small, individually, to satisfy the request. 

Imagine memory as a large bar divided into sections. Programs are loaded into these sections. When a program finishes, the section it occupied becomes free space. Over time, free space becomes fragmented as programs of various sizes come and go, leaving behind non-contiguous free blocks. 

Here's a breakdown of key points about external fragmentation:

Cause:

Dynamic memory allocation, where memory is allocated and deallocated as processes come and go.

Impact:

Even though total free memory might be sufficient, the fragmented free space cannot be used by new processes because it's not in a single contiguous chunk. This can lead to the system failing to allocate memory despite having enough free memory overall.

There are techniques to address external fragmentation, like compaction (reorganizing memory to group free space together) but it can be time-consuming. Memory allocation algorithms can also be designed to minimize fragmentation.