What are the different memory defragmentation techniques used?

There are several memory defragmentation techniques used in operating system memory management. Some of the commonly used techniques include:

1. Compaction: This technique involves moving the allocated memory blocks together to create a larger contiguous free memory space. It helps in reducing external fragmentation.

2. Paging: In this technique, the physical memory is divided into fixed-sized blocks called pages, and the logical memory is divided into fixed-sized blocks called page frames. It helps in reducing external fragmentation by allowing non-contiguous allocation of memory.

3. Segmentation: This technique divides the logical memory into variable-sized segments, which can be allocated to processes. It helps in reducing external fragmentation by allowing non-contiguous allocation of memory.

4. Buddy System: This technique involves dividing the memory into fixed-sized blocks and allocating them in powers of two. It helps in reducing external fragmentation by merging adjacent free blocks to create larger free blocks.

5. Garbage Collection: This technique is used in languages with automatic memory management. It involves identifying and reclaiming memory that is no longer in use, thereby reducing fragmentation.

These techniques are used to optimize memory utilization and improve the overall performance of the operating system.