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How to tell for sure if PAE (Physical Address Extensions) is enabled or not?
There is a SPECIFIC command I can use? I can read a registry value or something? (Windows 7 32 bits)

I have found this on Internet but it doesn't answer my question:

If your server has hot-add memory ability (ability to add more memory without shutting down the server !!) or data execution prevention (DEP) is enabled then PAE will be enabled automatically !!

It only reformulate the question as "does my Qosmio x505 laptop support hot-add memory?"

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1  
Having PAE does not automatically imply that all of the features that it allows will be available. It is incredibly rare, and almost completely unnecessary for home computers and laptops to support hot-plugging memory and I would be incredibly surprised if your system did. –  Mokubai Aug 9 '11 at 18:14
    
"Having PAE does not automatically imply" - - - I know, and this is why I want to VERIFY it. –  Altar Aug 9 '11 at 18:19
    
Could you accept Victor's answer below? It does actually answer the question. –  Dan Dascalescu Jan 7 '13 at 2:29

5 Answers 5

up vote 3 down vote accepted

How to tell for sure if PAE (Physical Address Extensions) is enabled or not?

On any modern Intel/AMD (x86/x64) system with hardware-level DEP, PAE is enabled out of the box on Windows XP (SP2?) and up, since it's required for the DEP feature to work.

"does my Qosmio x505 laptop support hot-add memory?"

No, it most assuredly does not.

Hot-add RAM is generally only found on high-end server hardware.

Edit:

According to MSDN Entry for PAE, it's enabled by default under certain (common) conditions:

Windows automatically enables PAE if DEP is enabled on a computer that supports hardware-enabled DEP, or if the computer is configured for hot-add memory devices in memory ranges beyond 4 GB. If the computer does not support hardware-enabled DEP or is not configured for hot-add memory devices in memory ranges beyond 4 GB, PAE must be explicitly enabled.

So, if the system is booted with PAE force-enabled or supports hardware DEP, PAE is on. That's every single system that's come with Vista or Windows 7 pre-installed, and a significant number of XP systems as well (late P4, Core Solo/Duo, Core 2 systems). The only caveat is if someone has gone out of their way to force disable it by editing the boot.ini file (for XP) or modify the BCD (for Vista/7).

As for how to see that it's enabled, I'm not sure. In XP, if you right click on My Computer and select Properties, the General tab will say Physical Address Extension at the bottom if PAE is enabled. 64-bit Win 7 systems don't seem to say, probably because PAE is always enabled on such systems. 32-bit Win 7 may say something similar in the System Control Panel, but until I can check my home laptop, I can't tell you for sure -- it's the only 32-bit Win 7 system I have access to, all my others are 64-bit.

There doesn't seem to be any registry entry that tells whether or not it's on.

Ultimately, the point is that it's safe to assume it's on unless you have a good reason to believe it's not. If you're writing code that depends on it, use the IsProcessorFeaturePresent function, that's what it's there for.

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Sorry but you didn't answer my question AT ALL! You just told us how its YOUR laptop. I didn't asked that. –  Altar Aug 9 '11 at 18:11
    
I only mentioned the named laptop because you did. If that's what you own, PAE is on unless you've gone to the trouble to disable it. See my edit for more info. –  afrazier Aug 9 '11 at 19:09
    
Thanks. Accepted (because of the 'MSDN Entry for PAE' link). –  Altar Aug 9 '11 at 20:22
1  
There is an actual answer to your question posted below by ''Victor Drobysh''. Could you accept that one instead? –  rustyx Sep 8 '12 at 10:06
    
PAE is always off on 64 bits machines. You don't need 4 bits of address extensions there. (PAE makes the page table 36 bits wide on 32 bits systems; on 64 bits systems it's already 48 bits wide) –  MSalters Jul 16 '13 at 11:47

A laptop almost certainly does not support hot-add memory. That feature only exists on certain high-end servers.

Windows XP SP2 and later versions of the client OS do not support more than 4GB of memory in 32 bit mode, even with PAE enabled because of driver compatibility issues. PAE is only used so the OS can access the NX bit.

See http://msdn.microsoft.com/en-us/windows/hardware/gg487512

If your CPU supports the NX bit, unless you are booting with the /NOPAE flag the kernel is probably using PAE for hardware DEP support.

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Sorry but you didn't answer my question AT ALL! As you said, I also know that P R O B A B L Y my computers has PAE enabled. What I have asked is how do I actually verify it. Computers should not be bibles - to just believe it. We should be able to verify it somehow. –  Altar Aug 9 '11 at 18:14
    
Go to the system control panel (sysdm.cpl). In the general page in the lower right corner it'll list how much memory you have installed. Below that if it says "Physical Address Extension" then PAE is being used. If it does not, PAE is not being used. –  Chris Smith Aug 9 '11 at 18:56
    
Ok I guess those instructions only work on XP. I don't have any 32 bit Windows 7 or Vista systems to look at but it must be on one of the system info screens. –  Chris Smith Aug 9 '11 at 19:05
    
Hi Chris. I cannot see indeed that screen on my Win 7 laptop. When I press Win+Break keys to see system's properties there is also no mention of pae –  Altar Aug 9 '11 at 20:08
    
@Altar: why would you believe the Bible without question? –  Dan Dascalescu Jan 7 '13 at 2:30

To use the graphical user interface to determine whether PAE is enabled, follow these steps:

  1. Click Start, click Run, type wbemtest in the Open box, and then click OK.
  2. In the Windows Management Instrumentation Tester dialog box, click Connect.
  3. In the box at the top of the Connect dialog box, type root\cimv2, and then click Connect.
  4. Click #Enum Instances".
  5. In the Class Info dialog box, type Win32_OperatingSystem in the Enter superclass name box, and then click OK.
  6. In the Query Result dialog box, double-click the top item. Note this item starts with "Win32_OperatingSystem.Name=Microsoft..."
  7. In the Object editor dialog box, locate the PAEEnabled property in the Properties area and double-click on it.
  8. In the Property Editor dialog box, note the value in the Value box.
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Awesome! I would never have found this :) Thank you –  rustyx Sep 8 '12 at 10:05
    
Works perfectly on windows 7. I should note that you can enable it by editing the BCD, EasyBCD makes it simple... with a trial. –  Ray Feb 3 '13 at 5:01

There is a registry setting that will tell you whether Physical Address Extension (PAE) is enabled.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PhysicalAddressExtension

If it is set to 1, then the kernel with PAE support was loaded at startup.

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WMI will give you this via the command line util 'WMIC', for example:

C:\> wmic os get PAEEnabled
PAEEnabled
TRUE

C:\>
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