address space

In computing, an address space defines a range of discrete addresses, each of which may correspond to a physical or virtual memory register, a network host, peripheral device, disk sector or other logical or physical entity. A memory address identifies a physical location in computer memory, somewhat similar to a street address in a town. The address points to the location where data is stored, just like your address points to where you live. In the analogy of a person's address, the address space would be an area of locations, such as a neighborhood, town, city, or country. Two addresses may be numerically the same but refer to different locations, if they belong to different address spaces. This is similar to your address being, say, "32, Main Street", while another person may reside in "32, Main Street" in a different town from yours.
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<operating system, architecture> The range of addresses which a processor or process can access, or at which a device can be accessed. The term may refer to either physical address or virtual address.
The size of a processor's address space depends on the width of the processor's address bus and address registers.
Each device, such as a memory integrated circuit, will have its own local address space which starts at zero. This will be mapped to a range of addresses which starts at some base address in the processor's address space.
Similarly, each process will have its own address space, which may be all or a part of the processor's address space. In a multitasking system this may depend on where in memory the process happens to have been loaded. For a process to be able to run at any address it must consist of position-independent code. Alternatively, each process may see the same local address space, with the memory management unit mapping this to the process's own part of the processor's address space.
(1999-11-01)