In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
, 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
A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit that examines all references to computer memory, memory, and translates the memory addresses being referenced, known as virtual mem ...
(MMU) between the
CPU and the memory bus.
There may be more than one level of mapping. For example, on multiprocessor configurations of the
IBM S/360,
S/370 and successors, IBM distinguishes among
#Virtual address seen by the program
#Real address, the result of translating a virtual address
#Absolute address, the result of mapping a real address using a low-storage prefix
[
] assigned to each CPU.
Computer memory
The physical address of computer memory banks may be mapped to different logical addresses for various purposes.
In a system supporting
virtual memory
In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a ver ...
, 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.
Notes
References
See also
*
Memory segment
*
Flat memory model
*
Memory address
{{DEFAULTSORT:Logical Address
Virtual memory