Explain the concept of segmentation in memory management.

Segmentation in memory management is a technique that divides a computer's memory into different segments or sections.

In more detail, segmentation is a method used in operating systems to make the most efficient use of memory. It is a non-contiguous method, meaning that the segments can be scattered throughout the memory rather than being in one continuous block. Each segment represents a logical unit such as a procedure, a block of data, or a program module. These segments can vary in size and are dynamically allocated, allowing for more flexibility and better memory utilisation.

The operating system maintains a segment table for each process, which contains the details of each segment such as its base address and limit. The base address indicates the starting physical address where the segments reside in memory, while the limit specifies the length of the segment. When a segment is referenced, the operating system checks the segment table to ensure that the reference is valid and within the limit of the segment. This helps to prevent errors and protect the system from unauthorized access.

Segmentation also facilitates sharing and protection. Different segments can be shared among processes, and protection can be applied at the segment level. For example, one segment could be read-only, while another could be read-write. This level of control enhances the security and efficiency of the system.

However, segmentation can also lead to issues such as external fragmentation, where free memory is broken up into non-contiguous blocks. This can make it difficult to find a large enough block of contiguous free memory for a new segment, even if there is enough total free memory. This problem can be mitigated through techniques such as compaction, which involves moving segments in memory to create larger blocks of contiguous free memory.

In conclusion, segmentation is a crucial concept in memory management that allows for efficient and flexible use of memory, while also providing mechanisms for sharing and protection. However, it also presents challenges such as external fragmentation, which must be managed effectively to maintain system performance.