Compaction refers to a technique for overcoming external fragmentation in computer memory management. It involves rearranging the memory blocks to reduce or eliminate the fragmentation and make efficient use of available memory.

External fragmentation occurs when free memory is scattered throughout the memory space in small, non-contiguous blocks. This can happen due to the allocation and deallocation of variable-sized memory blocks. As a result, even though there may be enough free memory to satisfy a memory allocation request, it may not be available in a contiguous block, leading to inefficient memory utilization.

Compaction is a process of rearranging memory blocks to create larger contiguous blocks of free memory. It involves moving allocated blocks and adjusting memory addresses to eliminate the gaps between them. The goal is to create a single large block of free memory, which can then be used to satisfy larger memory allocation requests.

Here is a detailed explanation of how compaction works:

1. Identify fragmented memory: The first step is to identify the areas of memory that are fragmented and contain small free blocks.

2. Relocate allocated blocks: The next step is to move the allocated blocks towards one end of the memory space, typically towards the lower addresses. This involves updating memory addresses in the process control blocks (PCBs) and any pointers or references to the memory blocks.

3. Adjust memory addresses: After relocating the allocated blocks, the memory addresses need to be adjusted to reflect the new positions. This may involve updating pointers, references, and any other data structures that store memory addresses.

4. Create a large block of free memory: As the allocated blocks are moved, the gaps between them are eliminated, creating a larger contiguous block of free memory.

5. Update memory management data structures: Finally, the memory management data structures, such as the free block list or bitmap, need to be updated to reflect the changes in the memory layout.

By compacting the memory and eliminating external fragmentation, compaction improves memory utilization and reduces the likelihood of memory allocation failures due to insufficient contiguous free memory. However, compaction can be a costly operation in terms of time and computational resources, especially if there are many allocated blocks that need to be moved. Therefore, it is typically used in situations where external fragmentation becomes a significant problem and memory compaction can be performed efficiently.