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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 ...
Diagram of relationship between the virtual and physical address spaces. In computing, a physical address (also real address, or binary address), is a memory address that is represented in the form of a binary number on the address bus circuitry in order to enable the data bus to access a particular storage cell of main memory, or a register of memory-mapped I/O device.
The physical address of computer memory banks may be mapped to different logical addresses for various purposes. In a system supporting virtual memory, there may actually not be any physical memory mapped to a logical address until an access is attempted. The access triggers special functions of the operating system which reprogram the MMU to ...
Paging is one way of allowing the size of the addresses used by a process, which is the process's "virtual address space" or "logical address space", to be different from the amount of main memory actually installed on a particular computer, which is the physical address space.
On the 360/65, on S/370 models without DAT and when running with translation turned off, there are only a flat real address space and a flat absolute address space. On the 360/67, S/370 and successors through S/390, when running with translation on, addresses contain a segment number, a page number and an offset. Although early models supported ...
The basic logical address space is 32K words, but the high 4K of physical address space (addresses 160000 8 through 177777 8 in the absence of memory management) are not populated because input/output registers on the bus respond to addresses in that range. So originally, a fully expanded PDP-11 had 28K words, or 56 kbytes in modern terms.
Relationship between pages addressed by virtual addresses and the pages in physical memory, within a simple address space scheme. Physical memory can contain pages belonging to many processes. Pages can be held on disk if seldom used, or if physical memory is full. In the diagram above, some pages are not in physical memory.
The offset part of the logical address contains an offset inside the segment, i.e. the physical address can be calculated as physical_address = segment_part × 16 + offset, if the address line A20 is enabled, or (segment_part × 16 + offset) mod 2 20, if A20 is off. [clarification needed] Every segment has a size of 2 16 bytes.