64bit Applications and Memory Limits

Can someone explain to me how 64 bit applications, a 64bit OS, and a 64 bit CPU fit together to establish how much memory is addressable by some application?

For example, how is addressable memory for an application affected if you run a 64bit application on a 64bit CPU, with a 32bit OS?

Or wha开发者_Python百科t about a 64bit CPU with a 64bit OS and a 32bit application?

What happens when you run a 64bit application on a 32bit CPU?

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You can't run a 64-bit application on a 32-bit CPU/OS.

A 64-bit OS running on a 64-bit processor has effectively unlimited memory. The address space is 0 to 2^64, or 18.4 exabytes.

A 32-bit application running on a 64-bit OS/processor gets the 32-bit address space, which is roughly 4GB.

More detail: http://cnx.org/content/m13082/latest/