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In computing, a logical address is the address at which an item (memory cell, storage element, network host) appears to reside from the perspective of an executing application program. A logical address may be different from the physical address due to the operation of an address translator or mapping function.
Address spaces are created by combining enough uniquely identified qualifiers to make an address unambiguous within the address space. For a person's physical address, the address space would be a combination of locations, such as a neighborhood, town, city, or country. Some elements of a data address space may be the same, but if any element ...
Usually, flash memory controllers also include the "flash translation layer" (FTL), a layer below the file system that maps host side or file system logical block addresses (LBAs) to the physical address of the flash memory (logical-to-physical mapping). The LBAs refer to sector numbers and to a mapping unit of 512 bytes.
The MMU consists of a context register, a segment map and a page map. Virtual addresses from the CPU are translated into intermediate addresses by the segment map, which in turn are translated into physical addresses by the page map. The page size is 2 KB and the segment size is 32 KB which gives 16 pages per segment. Up to 16 contexts can be ...
However, with the introduction of virtual memory most application programs do not deal directly with physical addresses. Instead, they use logical or virtual addresses, which are translated to physical addresses by the computer's memory management unit (MMU) and the operating system's memory mapping mechanisms.
A page table is a data structure used by a virtual memory system in a computer to store mappings between virtual addresses and physical addresses. Virtual addresses are used by the program executed by the accessing process, while physical addresses are used by the hardware, or more specifically, by the random-access memory (RAM) subsystem. The ...
The advantages of having an IOMMU, compared to direct physical addressing of the memory (DMA), include [citation needed]: . Large regions of memory can be allocated without the need to be contiguous in physical memory – the IOMMU maps contiguous virtual addresses to the underlying fragmented physical addresses.
1:1 mapping of unique addresses to one hardware register (physical memory location). Involves checking every line of the address bus. Incomplete (partial) decoding n:1 mapping of n unique addresses to one hardware register. Partial decoding allows a memory location to have more than one address, allowing the programmer to reference a memory ...