Incomputing, anaddress space defines a range of discrete addresses, each of which may correspond to anetwork host,peripheral device,disk sector, amemory cell or other logical or physical entity.
Forsoftware programs to save and retrieve stored data, each datum must have an address where it can be located. The number of address spaces available depends on the underlying address structure, which is usually limited by thecomputer architecture being used. Often an address space in a system withvirtual memory corresponds to a highest level translation table, e.g., asegment table inIBM System/370.
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, theaddress 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 in the address is different, addresses in said space will reference different entities. For example, there could be multiple buildings at the same address of "32 Main Street" but in different towns, demonstrating that different towns have different, although similarly arranged,street address spaces.
An address space usually provides (or allows) a partitioning to several regions according to themathematical structure it has. In the case oftotal order, as formemory addresses, these are simplychunks. Like the hierarchical design ofpostal addresses, some nested domain hierarchies appear as adirected ordered tree, such as with theDomain Name System or adirectory structure. In theInternet, theInternet Assigned Numbers Authority (IANA) allocates ranges ofIP addresses to various registries so each can manage their parts of the global Internet address space.[1]
Uses of addresses include, but are not limited to the following:
Another common feature of address spaces aremappings and translations, often forming numerous layers. This usually means that some higher-level address must be translated to lower-level ones in some way. For example, afile system on alogical disk operates usinglinear sector numbers, which have to be translated toabsoluteLBA sector addresses, in simple cases, viaaddition of the partition's first sector address. Then, for a disk drive connected viaParallel ATA, each of them must be converted tologicalcylinder-head-sector address due to the interface historical shortcomings. It is converted back to LBA by thedisk controller, then, finally, tophysicalcylinder,head andsector numbers.
TheDomain Name System maps its names to and from network-specific addresses (usually IP addresses), which in turn may be mapped tolink layer network addresses viaAddress Resolution Protocol.Network address translation may also occur on the edge ofdifferent IP spaces, such as alocal area network and the Internet.
An iconic example of virtual-to-physical address translation isvirtual memory, where differentpages ofvirtual address space map either topage file or to main memoryphysical address space. It is possible that several numerically different virtual addresses all refer to one physical address and hence to the same physical byte ofRAM. It is also possible that a single virtual address maps to zero, one, ormore than one physical address.