8GB of RAM to fully use 64bit memory addressing with 64bit Server

[Guest JM]

I was told by someone that you must use 8GB of RAM to fully use 64bit memory

addressing. I have never heard of this and I can't find any information on it.

[Guest dennis]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Server

 

JM wrote:

> I was told by someone that you must use 8GB of RAM to fully use 64bit memory

> addressing. I have never heard of this and I can't find any information on it.

>

 

http://forums.anandtech.com/messageview.aspx?catid=83&threadid=2214112&enterthread=y

[Guest JM]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

I read all of those responses but I probably should have given more

information. I currently test a 32bit application that is being ported to

64bit. I needed to know whether or not I would be able to properly test the

changes using only 4GB of RAM on a 64bit OS. I was told that the memory space

on a 4GB machine is only using the 32bit memory space and that I would need

to have over 4GB of RAM to exercise the 64bit memory space.

[Guest Justin Rich]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

only if your app needs to use large amounts of memory.

if you think your app will eat more than 2gb of user space, then its worth

testing.

 

i would say over all your pretty safe using 4gb of ram to test 64 bit

because of the way the VMM works.

 

I think the only real concern you would have for over 4gb is if you were

testing a 32bit app on a 64bit system. in that case there is a boot option

that will allow you to have apps start loading above the 4gb mark to see if

they are handled correctly..

 

 

"JM" <JM@discussions.microsoft.com> wrote in message

news:BA16CAD8-AC5E-403F-BEA5-8BCE97C061CF@microsoft.com...

>I read all of those responses but I probably should have given more

> information. I currently test a 32bit application that is being ported to

> 64bit. I needed to know whether or not I would be able to properly test

> the

> changes using only 4GB of RAM on a 64bit OS. I was told that the memory

> space

> on a 4GB machine is only using the 32bit memory space and that I would

> need

> to have over 4GB of RAM to exercise the 64bit memory space.

[Guest Bruce Sanderson]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

You may find the article at

http://members.shaw.ca/bsanders/WindowsGeneralWeb/RAMVirtualMemoryPageFileEtc.htm

useful.

 

See in particular sections 2.2 and 2.4 and 3.

 

If your appplication is built to use the 64 bit instruction set, the 64 bit

version of Windows will create a "64 bit" adress space for it - 8 TB of

private address space, regardless of how much RAM is in the computer. If

your application then proceeds to use more of the address space than there

is available RAM, some of it will be paged out. This will affect

performance, but not the function of the application.

 

Even on 64 bit Windows installation, 32 bit applications will only get a 32

bit address space - 2 GB or private space (unless the /3GB boot switch is

used or the application uses the AWE API - sections 2.5 and 2.6).

 

--

Bruce Sanderson

http://members.shaw.ca/bsanders

 

It is perfectly useless to know the right answer to the wrong question.

 

 

 

"JM" <JM@discussions.microsoft.com> wrote in message

news:BA16CAD8-AC5E-403F-BEA5-8BCE97C061CF@microsoft.com...

>I read all of those responses but I probably should have given more

> information. I currently test a 32bit application that is being ported to

> 64bit. I needed to know whether or not I would be able to properly test

> the

> changes using only 4GB of RAM on a 64bit OS. I was told that the memory

> space

> on a 4GB machine is only using the 32bit memory space and that I would

> need

> to have over 4GB of RAM to exercise the 64bit memory space.

[Guest Gander]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Bruce Sanderson skrev:

> Even on 64 bit Windows installation, 32 bit applications will only get a

> 32 bit address space - 2 GB or private space (unless the /3GB boot

> switch is used or the application uses the AWE API - sections 2.5 and 2.6).

>

 

On 64bit Windows the application will be allowed to grow to 4GB, if the

largeaddressawarebit is set. I don't think the /3gb switch exits on

64bit Win

[Guest Bruce Sanderson]

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Re: 8GB of RAM to fully use 64bit memory addressing with 64bit Ser

 

Gander: thank you for pointing that out!

 

I thought I remembered reading something about that and found it in

http://support.microsoft.com/?kbid=294418 and also

http://msdn.microsoft.com/en-us/library/aa366778.aspx.

 

I've made some updates to the document at

http://members.shaw.ca/bsanders/WindowsGeneralWeb/RAMVirtualMemoryPageFileEtc.htm:

 

1. revised section 2.3 Pagefile to reflect that most computers these days

have 1 GB RAM or more

2. added 2.5.3. about 32 bit applications with the

IMAGE_FILE_LARGE_ADDRESS_AWARE bit on will get 4 GB of private address space

on 64 bit Windows as you pointed out.

3. verified the maximum RAM for 32 bit and 64 bit Windows version from the

referenced Microsoft documents

4. other minor updates.

 

I noticed that the document at

http://msdn.microsoft.com/en-us/library/aa366778.aspx says"

 

"User-mode virtual address space for 64-bit processes" is 2 GB unless the

IMAGE_FILE_LARGE_ADDRESS_AWARE bit is on.

 

However, the "Benefits of Microsoft Windows x64 Editions" downloadable from

http://www.microsoft.com/windowsserver2003/techinfo/overview/x64benefits.mspx

appears to contradict this with this statement:

 

"Windows x64 Editions can address a full 16 TB of virtual memory by using a

flat addressing model. This 16 TB is divided up into equal buckets of 8 TB

of virtual address space for applications and 8 TB for the operating

system."

 

If anyone can definitively clarify this (someone from the Microsoft Windows

kernel team perhaps?) I'd appreciate it.

 

If anyone notices any other errors or has other comments about it, please

post here.

 

--

Bruce Sanderson

http://members.shaw.ca/bsanders

 

It is perfectly useless to know the right answer to the wrong question.

 

 

 

"Gander" <gander@.> wrote in message

news:%23VW4r$59IHA.1196@TK2MSFTNGP05.phx.gbl...

> Bruce Sanderson skrev:

>

>> Even on 64 bit Windows installation, 32 bit applications will only get a

>> 32 bit address space - 2 GB or private space (unless the /3GB boot switch

>> is used or the application uses the AWE API - sections 2.5 and 2.6).

>>

>

> On 64bit Windows the application will be allowed to grow to 4GB, if the

> largeaddressawarebit is set. I don't think the /3gb switch exits on 64bit

> Win