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Main memory (Primary storage) – GiB [citation needed] [original research] in size. Best access speed is around 10 GB/s. [9] In the case of a NUMA machine, access times may not be uniform; Disk storage (Secondary storage) – Terabytes in size. As of 2017, best access speed is from a consumer solid state drive is about 2000 MB/s [10]
Tertiary storage or tertiary memory [7] is a level below secondary storage. Typically, it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; such data are often copied to secondary storage before use. It is primarily used for archiving rarely ...
The term memory is often synonymous with the terms RAM, main memory, or primary storage. Archaic synonyms for main memory include core (for magnetic core memory) and store. [3] Main memory operates at a high speed compared to mass storage which is slower but less expensive per bit and higher
Each allocated memory block is given a master descriptor with the properties of the block — physical address, size, and whether it is present in main memory or not, in which case on first access the block must be allocated, or if there is an address, it is an address on secondary storage and must be loaded to main memory.
In computer operating systems, memory paging (or swapping on some Unix-like systems) is a memory management scheme by which a computer stores and retrieves data from secondary storage [a] for use in main memory. [1] In this scheme, the operating system retrieves data from secondary storage in same-size blocks called pages.
In early systems, there was a clear distinction between main memory and any secondary storage. In order to process data, programs would use explicit code to read data from secondary storage into main memory, manipulate it in main memory, and then use more code to write it back out to secondary storage again.
Unlike virtual storage—paging or segmentation, rollout/rollin does not require any special memory management hardware; however, unless the system has relocation hardware such as a memory map or base and bounds registers, the program must be rolled back in to its original memory locations. Rollout/rollin has been largely superseded by virtual ...
An implementation of virtual memory on a system using segmentation without paging requires that entire segments be swapped back and forth between main memory and secondary storage. When a segment is swapped in, the operating system has to allocate enough contiguous free memory to hold the entire segment.