Physical address

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In computing, a physical address, also real address, or binary address, is the memory address that is electronically (in the form of binary number) presented 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 address refer to 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 network's data link layer, not on physical layer, as the name would suggest.

Note: There are two basic types of physical addresses when referencing Ethernet which are large and fixed physical addresses and proNET, which has small relatively easy to configure addresses.^{[citation needed]}

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).

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)