Re: 4GB memory
- From: "James Johnson" <jamesone@xxxxxxxxxxxx>
- Date: Mon, 15 Dec 2008 07:03:34 -0600
Ken,
wonder if you could clear something up for me. I am running Vista Ultimate 64 bit. I understand the 4 GB address space limitation of the 32 bit version and from what I've read the 64 bit version allocates 4 GB address space using the WOW64 for 32 bit apps. Since the OS (64 bit) doesn't need to share this space, the whole 4GB is available to the 32 bit app. if it is compiled with a large address space switch or something of that nature.. In the articles I've read there seems to be a lot of confusion here. Some have said that the switch is only for apps running on the 32 bit version and that it doesn't make any difference on the 64 bit version (I guess meaning all 32 bit apps on 64 bit will have the 4 GB space available to it). I kind of think that the flag or switch would need to be set in either case, but I'm not sure. One article said that most developers set that flag on their 32 bit apps as it doesn't hurt anything (I think that some other boot flag would have to be set in conjunction with it on 32 bit systems etc.) Could you please help clear this up for me. Seems the more stuff you read on the web the more confused you get lol. Thanks for your help.
Jim
"Ken Blake, MVP" <kblake@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:l4kak4pctco7lh3h5vnlmb5klvr7aaj2aj@xxxxxxxxxx
On Sun, 14 Dec 2008 11:35:41 -0500, "JBrown" <jbrown15@xxxxxxxxxx>
wrote:
Is it true that to use 4GB memory you need 64 bit Vista?
Yes. Two points:
1. All 32-bit client versions of Windows (not just Vista/XP) have a
4GB address space. That's the theoretical upper limit beyond which you
can not go.
But you can't use the entire 4GB of address space. Even though you
have a 4GB address space, you can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and is not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but can
range from as little as 2GB to as much as 3.5GB. It's usually around
3.1GB.
Note that the hardware is using the address *space*, not the actual
RAM itself. The rest of the RAM goes unused because there is no
address space to map it too.
2. For most users of Vista, that average value of 3.1GB is as much RAM
or even more RAM than most people can make effective use of. Unless
you run particularly memory-hungry programs, installing more RAM than
that does next to nothing for you and is a waste of money.
--
Ken Blake, Microsoft MVP - Windows Desktop Experience
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