Physical Address Information
In computing, a physical address, also real address, or binary address, is the memory address that is represented in the form of a binary number on the computer address bus circuitry in order to enable the data bus to access a particular storage cell of main memory.
In a computer with virtual memory, the term physical address is used mostly to differentiate from a virtual address. In particular, in computers utilizing memory management unit (MMU) to translate memory addresses, the virtual and physical addresses refer to an address before and after MMU translation respectively.
In computer networking, physical address is sometimes a synonym of MAC address. The address is actually used on the network's data link layer, not on the physical layer, as the name would suggest.
Unaligned addressing
Depending upon its underlying computer architecture, the performance of a computer may be hindered by unaligned access to memory. As an example, a 16 bit computer with a 16 bit memory data bus such as an Intel 8086 generally works most efficiently if the access is aligned to an even address. In that case fetching one 16 bit value requires a single memory read operation, a single transfer over a data bus. Obviously, if the 16 bit data value starts at an odd address, the processor may actually need to perform two memory read cycles to load the value into it, i.e. one for the low address (throwing half of it away) and then a second to load the high address (again throwing half of the retrieved data away). In fact, on some architectures (such as the Motorola 68000 family), unaligned memory accesses will result in an exception being raised (usually resulting in a software exception being raised like POSIX's SIGBUS).
See also
- Address constant
- Addressing mode
- Address space
- Page address register
- Pointer (computer science)
- Primary storage, also known as main memory
- Virtual memory
- Virtual address, also known as logical address
- Page table
- Memory management unit (MMU)
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Categories: Computer memory | Virtual memory | Data types
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