Segmentatietabellen

Segmentatietabellen, also known as segmentation tables or segment tables, are a core component of memory management in computer operating systems. They are used in systems that employ memory segmentation, a memory management technique where memory is divided into variable-sized blocks called segments. Each segment typically corresponds to a logical unit of a program, such as a code segment, data segment, or stack segment.

A segmentatietabel is essentially an array where each entry corresponds to a segment. Each entry in the table, often called a segment descriptor, contains crucial information about a particular segment. This information typically includes the base address of the segment in physical memory and its limit or size. When a program accesses a memory location, the CPU uses the segment number to look up the corresponding entry in the segmentatietabel.

The segment number is usually part of the logical address generated by the CPU. This logical address is then translated into a physical address. The segmentatietabel entry provides the starting physical address of the segment. The offset within the logical address is then added to this base address to calculate the final physical address. The limit value is used to perform bounds checking, ensuring that the access stays within the allocated segment and preventing illegal memory accesses.

Segmentation with segmentatietabellen allows for flexible memory allocation and protection. It enables programs to be non-contiguous in physical memory and facilitates sharing of code or data segments between different processes. However, it can also lead to external fragmentation if segments are allocated and deallocated frequently, creating small, unusable gaps in physical memory.