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The Multics operating system is probably the best known system implementing segmented memory. Multics segments are subdivisions of the computer's physical memory of up to 256 pages, each page being 1K 36-bit words in size, resulting in a maximum segment size of 1MiB (with 9-bit bytes, as used in Multics). A process could have up to 4046 segments.
In virtual memory systems the operating system limits how a process can access the memory. This feature, called memory protection , can be used to disallow a process to read or write to memory that is not allocated to it, preventing malicious or malfunctioning code in one program from interfering with the operation of another.
In modern operating systems, memory which is accessed less frequently can be temporarily stored on a disk or other media to make that space available for use by other programs. This is called swapping , as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand.
When the operating system requested memory to load a program, or a program requested more memory to hold data from a file for instance, it would call the memory handling library. This examined the mappings to look for an area in main memory large enough to hold the request. If such a block was found, a new entry was entered into the table.
These patterns have implications for locality of reference, parallelism, and the distribution of workload in shared memory systems. memory address The address of a location in a memory or other address space. memory architecture A memory architecture in a computer system, e.g. NUMA, uniform memory access, COMA, etc. memory card
An allocated memory block is represented with a handle. Get an access pointer to the allocated memory. Free the formerly allocated memory block. The handle can for example be implemented with an unsigned int. The module can interpret the handle internally by dividing it into pool index, memory block index and a version.
A free list (or freelist) is a data structure used in a scheme for dynamic memory allocation. It operates by connecting unallocated regions of memory together in a linked list, using the first word of each unallocated region as a pointer to the next. It is most suitable for allocating from a memory pool, where all objects have the same size.
In the case of operating systems that support virtual memory, the loader may not actually copy the contents of executable files into memory, but rather may simply declare to the virtual memory subsystem that there is a mapping between a region of memory allocated to contain the running program's code and the contents of the associated ...