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

  • Thread starter Thread starter JM
  • Start date Start date
J

JM

Guest
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.
 
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.
 
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.
 
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.
 
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
 
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
 
Back
Top