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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. Such mapping functions may be, in the case of a computer memory architecture, a memory management unit (MMU) between the CPU and the memory bus, or an address translation layer, e.g., the Data Link Layer, between the hardware and the internetworking protocols (Internet Protocol) in a computer networking system.

[edit] Computer memory

The physical address of computer memory banks may be mapped to different logical addresses for various purposes.

For example, the same physical memory may appear at two different logical addresses and if accessed by the program at one address, data will pass through the processor cache whereas if it is accessed at the other address, it will bypass the cache.

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 map the address to some physical memory, perhaps writing the old contents of that memory to disk and reading back from disk what the memory should contain at the new logical address. In this case, the logical address may be referred to as a virtual address.

[edit] Other Uses

Logical address or virtual address is also used in IBM's VM operating system and in Virtual Device Location.

[edit] See also

• Memory segment
• Flat memory model
• memory address

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.