.. _virt_address_space:

The Virtual Memory Address Space
----------------------------------

.. index:: logical addresses, virtual addresses

We have already discussed how the :term:`logical address` are referenced by
the program as it runs, but the :ref:`mmu` calculates the :term:`physical
address` before loading the address on to bus.  With a virtual memory
management system, the logical address space becomes a virtual address space
that uses the full range of memory addresses for each process (0 to 4 GB for
a 32 bit system).  

The virtual memory address space for each process is quite **sparse**.
Recall what the contiguous address space for a process looks like.  If
address space is sparse, then the heap is quite large, which mean that the
stack is unlikely to grow into other memory.  A large heap leaves plenty of
room for dynamically allocated memory and also for the memory addresses of
shared libraries (called DLLs in Windows).


.. figure:: local_mem_map.png
   :align: center

   The stack for each process grows down toward the global memory at the
   lower addresses.  Thus the stack grows into the heap.