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Virtual memory combines active RAM and inactive memory on DASD [a] to form a large range of contiguous addresses.. In computing, virtual memory, or virtual storage, [b] is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" [3] which "creates the illusion to users of a very large (main) memory".
In effect, physical main memory becomes a cache for virtual memory, which is in general stored on disk in memory pages. Programs are allocated a certain number of pages as needed by the operating system. Active memory pages exist in both RAM and on disk. Inactive pages are removed from the cache and written to disk when the main memory becomes ...
The early history of cache technology is closely tied to the invention and use of virtual memory. [citation needed] Because of scarcity and cost of semi-conductor memories, early mainframe computers in the 1960s used a complex hierarchy of physical memory, mapped onto a flat virtual memory space used by programs. The memory technologies would ...
Diagram of a CPU memory cache operation. In computing, a cache (/ k æ ʃ / ⓘ KASH) [1] is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere.
Virtual memory systems abstract between physical RAM and virtual addresses, assigning virtual memory addresses both to physical RAM and to disk-based storage, expanding addressable memory, but at the cost of speed. NUMA and SMP architectures optimize memory allocation within multi-processor systems. While these technologies dynamically manage ...
Most general purpose computers use a hybrid split-cache modified Harvard architecture that appears to an application program to have a pure Princeton architecture machine with gigabytes of virtual memory, but internally (for speed) it operates with an instruction cache physically separate from a data cache, more like the Harvard model. [1]
By reducing the I/O activity caused by paging requests, virtual memory compression can produce overall performance improvements. The degree of performance improvement depends on a variety of factors, including the availability of any compression co-processors, spare bandwidth on the CPU, speed of the I/O channel, speed of the physical memory, and the compressibility of the physical memory ...
Illustration of cache coloring. Left is virtual memory spaces, center is the physical memory space, and right is the CPU cache.. A physically indexed CPU cache is designed such that addresses in adjacent physical memory blocks take different positions ("cache lines") in the cache, but this is not the case when it comes to virtual memory; when virtually adjacent but not physically adjacent ...