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Virtual Machine and RAM

Posted on 2009-07-09
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Last Modified: 2012-05-07
If you have a machine that has 8GBs of RAM but is running a 32 Bit OS using only 3.7 GBs. Can a virtual Machine running on this box use all or any of the unused RAM or can it only be assigned RAM that the "Parent" OS has available?
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Question by:wdabbs
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by:Andres Perales
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Only RAM that the host os is supporting!
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by:willettmeister
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If I understand your question right then yes.  One of the points of Vmware is oversubscription so you don't have to have as much physical memory in the host as you have assigned to your guests.  If for some reason all of you guests begin using all of their memory then you will have problems but that is where DRS comes in to play.
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by:evan021702
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The host machine must be able to view all of the RAM in order to share it out to the VM.  If you cannot see all of your ram and are using an intel processor you could add /PAE (Physical Address Extension) to be able to see the additional ram on server 2003.
example boot.ini:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows Server 2003, Enterprise" /fastdetect /PAE
 
 
 
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by:wdabbs
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So.. in order to use the 8GBs in the machine.. the Host OS needs to be 64 Bit?
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by:wdabbs
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Yeah.. about that lol.. They are running Server2008 Standard
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by:evan021702
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No just use PAE if it is an intel processor.  See more here:
 
http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx  
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by:evan021702
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According to this yes, but let me see if any of the other admins are using PAE on 2008:
 
http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx
 
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by:willettmeister
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Windows can see more than 4Gb RAM using a 32-bit os.  You need to enable PAE.
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Andres Perales earned 200 total points
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PAE is only 32 GB max on Enterprise OS, if Standard stuck on 4 GB
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by:evan021702
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I think you are going to have to upgrade to enterprise to be able to see the 8GB of ram... Sorry.
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by:wdabbs
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Thank you all for the input!!
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by:wdabbs
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To clarify: Windows sees 8 GB of RAM in the Server 2008 system summary window, but appears to only use 4 GB when you right-click on My Computer and look at Properties the old-fashioned way. So 8 GB are "seen" but only 4 GB are addressed. The question is, can the extra 4 that are "seen" be used by a virtual system like VMWare or Hyper-V?
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by:evan021702
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How much do you see when you open task manager and go to performance?
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