Why won't 10.8.2 allocate over 3.7 GB of VM?

I'm talking about the VM used by the individual App, not the aggregate VM in use across the system.

In talking with an Apple tech person, we discovered that the app in question was a 32 bit app.

By definition, only able to address 4GB of memory.

The answer to "VM jumping up to more than the Fee Space on the Drive" is actually quite "simple."

Virtual Memory is not really what everyone thinks it is. Part of it is actually the application itself on disk. Another, and in most cases, the primary portion, is simply "allocated," but not used. And I put "Allocated" in quotes because it is not allocated in a physical sense on the disk, but in a table in memory.

Virtual Memory managemnt is a complex topic and for Mountain Lion, not documented. The Docs describing OSX virtual memory go back to Tiger for the most part. However, for Lion and Mountain Lion significant changes were made.

One of the things I was looking for was the answer to the question -- does OSX use "Eager Swap" or Lazy Swap" and what do those terms mean to OSX. One term means "allocate the disk space for swapping this App at Launch." The other means "don't allocate the disk space until it is needed to swap the app out."

Both are gross simplifications, but the basic idea.

As for adding more physical ram -- that was the "red herring" in this situation. Since I had 4 GB of ram, it was obscuring the fact that it was a 32bit App, which can only address 4GB or memory!

If I had had 8 or 16 GB, the question would have been more obvious -- Why is this App only using 4 GB or ram when there is another 4 or 12 GB available? Which would have made the answer more obvious.