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    <p>Zero, or practically Zero, memory is used by making a VirtualAlloc call with the reserve param. This will just reserve the address space within the process. The memory will not be used until you actually back the address with a page by using VirtualAlloc with the commit param. This is essentially the difference between virtual bytes, the amount of address space taken, and private bytes, the amount of committed memory. Both of your uses of VirtualAlloc() will reserve the same amount of memory so they are equivalent from the resource consumption side. I suggest that you do some reading on this before deciding to write your own allocator. One of the best sources for this is Mark Russinivich. You should check <a href="http://blogs.technet.com/b/markrussinovich/" rel="nofollow noreferrer">his blog</a>. He has written a few entries called pushing the limits which cover some of of this. If you want to get at the real nitty gritty details, then you should read his book (<a href="http://www.amazon.com/gp/search?ie=UTF8&amp;keywords=Microsoft+Windows+Internals&amp;tag=orgus-20&amp;index=books&amp;linkCode=ur2&amp;camp=1789&amp;creative=9325" rel="nofollow noreferrer">Microsoft Windows Internals</a>). This is by far the best reference that I have read on how windows manages the memory (and everything else).</p> <p>(Edit) Additional Information: The relevant pieces are the "Page Directory" and the "Page Table". According to my older copy of Microsoft Windows Internals... On x86, there is a single Page Directory for each process with 1024 entries. There are up to 512 page tables. Each 32 bit pointer used in the process is broken into 3 pieces [31-22]Page Directory Index, [21-12] is the Page Table Index, and [11-0] is the byte index in the page. When you use virtual alloc with the reserve param, the Page Directory Entry is created (32 bits), and the Page Table Entry is created 32 bits. At this time, the page is not created for the reserved memory. The best way to see this information is to use the Kernel Debugger. I would suggest using LiveKD (sysinternals). You can use liveKD without attaching a remote computer, but it doesn't allow live debugging. Load LiveKD, and select your process. Then you can run the !PTE command to examine the page table for the process.</p> <p>Again, I would suggest reading Inside Windows Internals. In my version (4th ed) there is a chapter(over 100 pages) that covers all of this with examples for walking through the various data structures in liveKD.</p>
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    1. COThe effect of VirtualAlloc on the memory it is reserving / commiting is clear. What I unclear is its overhead. Given the nature of VirtualAlloc, it is clear its overhead is outside of the memory it manages. I was unable to find anything about this overhead so far, even in SysInternals resources. Reserving and Commiting memory is very different in one respect - by reserving you are creating a new region, by committing you are only changing a state of individual page.
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    2. COAdded additional info on the PTE structure and how to see it in LiveKD.
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