Source : Free On-Line Dictionary of Computing

address space
     
         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)