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Memory segmentation is an operating system memory management technique of dividing a computer's primary memory into segments or sections.In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset (memory location) within that segment.
For example, in the tiny model CS=DS=SS, that is the program's code, data, and stack are all contained within a single 64 KB segment. In the small memory model DS=SS, so both data and stack reside in the same segment; CS points to a different code segment of up to 64 KB.
Pointer formats are known as near, far, or huge.. Near pointers are 16-bit offsets within the reference segment, i.e. DS for data and CS for code. They are the fastest pointers, but are limited to point to 64 KB of memory (to the associated segment of the data type).
MS-DOS is an example of a system that allocates memory in this way. An embedded system running a single application might also use this technique. A system using single contiguous allocation may still multitask by swapping the contents of memory to switch among users. Early versions of the MUSIC operating system used this technique.
A segmentation fault occurs when a program attempts to access a memory location that it is not allowed to access, or attempts to access a memory location in a way that is not allowed (for example, attempting to write to a read-only location, or to overwrite part of the operating system). The term "segmentation" has various uses in computing; in ...
The operating system loads the physical address of this segment into a base register and its size into a bound register. Virtual addresses seen by the program are added to the contents of the base register to generate the physical address. The address is checked against the contents of the bounds register to prevent a process from accessing ...
The term "segment" comes from the memory segment, which is a historical approach to memory management that has been succeeded by paging.When a program is stored in an object file, the code segment is a part of this file; when the loader places a program into memory so that it may be executed, various memory regions are allocated (in particular, as pages), corresponding to both the segments in ...
A hobby operating system may be classified as one whose code has not been directly derived from an existing operating system, and has few users and active developers. [ 132 ] In some cases, hobby development is in support of a " homebrew " computing device, for example, a simple single-board computer powered by a 6502 microprocessor .