The Old New Thing : August 2004

A table of contents now that the whole thing is over. I hope. The oft-misunderstood /3GB switch . It's simple to explain what it does, but people often misunderstand. Kernel address space consequences of the /3GB switch . An adverse consequence of the

Posted by oldnewthing | 36 Comments

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Friday, August 20, 2004 7:00 AM

The curious interaction between PAE and NX

Carmen Crincoli covered the interaction between PAE and NX on his own blog , so I'll merely incorporate his remarks by reference. (And notice again the concession to backwards compatibility. Without the backwards compatibility work, XP SP2 would have

Posted by oldnewthing | 5 Comments

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Friday, August 20, 2004 7:00 AM

Writing your own menu-like window

Hereby incorporating by reference the "FakeMenu" sample in the Platform SDK. It's in the winui\shell\fakemenu directory. For those who don't have the Platform SDK, what are you doing writing Win32 programs without the Platform SDK? Download it if it didn't

Posted by oldnewthing | 32 Comments

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Thursday, August 19, 2004 7:00 AM

Myth: In order to use AWE, you must enable PAE

Address Windowing Extensions (AWE) does not require PAE. I don't know why some people claim that it does, since it is so easy to demonstrate otherwise. Take a program that uses AWE. If you don't have one handy, you can use the one that comes in MSDN as

Posted by oldnewthing | 15 Comments

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Wednesday, August 18, 2004 7:00 AM

Myth: PAE increases the virtual address space beyond 4GB

This is another non sequitur. PAE increases the amount of physical memory that can be addressed by the processor, but that is unrelated to virtual address space. (Remember that PAE stands for Physical Address Extensions .) PAE increases the physical address

Posted by oldnewthing | 13 Comments

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Wednesday, August 18, 2004 7:00 AM

Why all these articles about PAE and /3GB?

Apparently there is some unrest in comment-land with people who are sick of this whole /3GB series . Why have I been spending over two weeks exploring the consequences of the /3GB switch and exploding various common myths about it? Because too many people

Posted by oldnewthing | 22 Comments

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Tuesday, August 17, 2004 7:00 AM

Why is the virtual address space 4GB anyway?

The size of the address space is capped by the number of unique pointer values. For a 32-bit processor, a 32-bit value can represent 2 32 distinct values. If you allow each such value to address a different byte of memory, you get 2 32 bytes, which equals

Posted by oldnewthing | 58 Comments

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Monday, August 16, 2004 7:01 AM

Myth: The /3GB switch lets me map one giant 3GB block of memory

Just because the virtual address space is 3GB doesn't mean that you can map one giant 3GB block of memory. The standard holes in the virtual address space are still there: 64K at the bottom, and 64K near the 2GB boundary . Moreover, the system DLLs continue

Posted by oldnewthing | 20 Comments

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Friday, August 13, 2004 7:00 AM

Why does Exchange recommend /3GB if you have more than 1GB of physical memory?

If you look through the Knowledge Base , you'll see an article that say that Exchange 2000 requires the /3GB switch with more than 1 gigabyte of physical RAM . Yet I've been writing all this time that /3GB has nothing to do with physical RAM. What's the

Posted by oldnewthing | 17 Comments

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Thursday, August 12, 2004 7:00 AM

Myth: The /3GB switch expands the user-mode address space of all programs

Only programs marked as /LARGEADDRESSAWARE are affected. For compatibility reasons, only programs that explicitly indicate that they are prepared to handle a virtual address space larger than 2GB will get the larger virtual address space. Unmarked programs

Posted by oldnewthing | 46 Comments

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Wednesday, August 11, 2004 8:11 AM

Myth: You need /3GB if you have more than 2GB of physical memory

Physical memory is not virtual address space. In my opinion, this is another non sequitur . I'm not sure what logical process led to this myth. It can't be a misapprehension of a 1-1 mapping between physical memory and virtual memory, because that mapping

Posted by oldnewthing | 38 Comments

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Tuesday, August 10, 2004 7:00 AM