Under the Hood of .NET Memory Management - Simple Talk

Chapter 7: The Windows Memory Model
It's worth pointing out that each process has its own page directory index, the address
of which is stored in a specific CPU register so as to be always available when a process
thread is running.
The mechanisms for 64-bit processes and 32-bit processes with physical address
extensions (PAE) are similar, but both involve more deeply nested table structures to
cope with overhead of the larger address space, and the virtual address structure also
differs. However, the principle is the same so, in the interests of clarity, I will leave
it there.
Page Table Entry
As you have hopefully deduced from the previous sections, the page table entry (PTE) is
the key piece of information in virtual addressing because it holds the physical memory
location of the virtual page. Perhaps even more crucially, it records whether the entry is
valid or not. When valid (i.e. the valid bit is set), the page is actually loaded in physical
memory. Otherwise (i.e. when invalid) there are one of several possible problems interfering
with the addressing process, the least of which will require the page to be reloaded
from the page file.
The PTE also stores some info about page security and usage info, but that's
another story.
Page Faults
When access is attempted to a virtual page with a PTE validity bit set to zero, it's called
a page fault. The requested page isn't in physical memory, so something else is going to
have to happen.
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