Memory segmentation is an working system memory management strategy of dividing a computer's major memory into segments or sections. In a computer system utilizing segmentation, a reference to a memory location consists of a value that identifies a segment and an offset (memory location) within that segment. Segments or sections are also used in object files of compiled programs when they're linked collectively right into a program image and when the image is loaded into memory. Segments could also be created for program modules, or for lessons of memory utilization equivalent to code segments and knowledge segments. Certain segments could also be shared between packages. Segmentation was initially invented as a technique by which system software program could isolate software processes (tasks) and knowledge they are utilizing. It was supposed to extend reliability of the techniques operating multiple processes simultaneously. In a system utilizing segmentation, pc memory addresses encompass a phase id and an offset throughout the phase.

A hardware memory management unit (MMU) is accountable for translating the section and offset right into a bodily deal with, and for performing checks to ensure the translation will be accomplished and that the reference to that section and offset is permitted. Every segment has a size and set of permissions (for example, learn, write, execute) associated with it. A course of is simply allowed to make a reference right into a phase if the type of reference is allowed by the permissions, and if the offset throughout the phase is within the range specified by the size of the section. In any other case, a hardware exception akin to a segmentation fault is raised. Segments could also be used to implement virtual memory. On this case each section has an related flag indicating whether or not it's present in principal Memory Wave or not. If a segment is accessed that isn't present in fundamental memory, an exception is raised, and the operating system will learn the section into memory from secondary storage.

Segmentation is one technique of implementing memory safety. Paging is one other, and they are often combined. The size of a memory phase is mostly not mounted and could also be as small as a single byte. Segmentation has been implemented several ways on varied hardware, with or without paging. Intel x86 memory segmentation doesn't fit either mannequin and is discussed individually under, and likewise in larger detail in a separate article. Associated with each segment is information that signifies the place the segment is situated in memory- the segment base. When a program references a memory location, the offset is added to the section base to generate a physical memory deal with. An implementation of virtual memory on a system using segmentation without paging requires that whole segments be swapped back and forth between main memory and MemoryWave Official secondary storage. When a section is swapped in, the operating system has to allocate sufficient contiguous free memory to hold your entire section. Often memory fragmentation results if there will not be sufficient contiguous memory despite the fact that there could also be enough in complete.

Instead of a memory location, the phase info includes the handle of a web page table for the phase. When a program references a memory location the offset is translated to a memory address using the page table. A section can be prolonged by allocating one other memory web page and including it to the section's web page table. An implementation of virtual memory on a system utilizing segmentation with paging normally solely strikes particular person pages again and forth between most important memory and secondary storage, similar to a paged non-segmented system. Pages of the phase can be positioned anyplace in most important memory and want not be contiguous. This usually ends in a decreased quantity of input/output between major and secondary storage and decreased memory fragmentation. The B5000 is outfitted with a section information desk referred to as the program Reference Desk (PRT) which is used to indicate whether or not the corresponding section resides in the primary Memory Wave, to keep up the bottom handle and the size of the section.

The later B6500 computer also implemented segmentation