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Author Topic: Access more memory, even on a 32-bit system  (Read 41193 times)

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Broni

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Access more memory, even on a 32-bit system
« on: December 19, 2008, 04:48:01 PM »
HERE

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No matter how much memory you have in your PC, you may not be getting the most out of your installed RAM.

A few little-known system tweaks can improve the way Windows manages memory, freeing up more RAM for your applications.

As described in an entry on the Microsoft Developer Network, all non-server 32-bit versions of Windows XP and Vista impose a memory limit of 4GB. Your system may allow you to install more than this amount of RAM, but with few exceptions, the extra memory won't do Windows or your applications any good.

Moreover, even if you have 4GB of memory installed in your PC, you may not be able to use it all. For example, if your video card comes with 1MB of memory and you have 4GB of RAM, your system actually has 5GB of memory physically installed. But Windows will use only 4GB of that total, regardless.

It gets worse: according to a comment posted to the MSDN article, Windows itself is getting only 3GB because the video card gets 1GB. This happens because the memory aperture — a portion of system memory — is used to work with the video system.

Ways to break through Windows' RAM ceiling

Fortunately, there are techniques you can use to get around Windows' system-memory limitations. One method is to use Physical Address Extension (PAE), a feature of x86 processors that lets 32-bit operating systems overcome the 4GB memory limit.

Another MSDN article explains that 32-bit Windows operating systems support PAE. Even though XP and Vista still cling to the 4GB limit with PAE enabled, the feature may help you get back some of your unused RAM.

In one or two rare cases, a developer may take advantage of PAE technology to get around the usual Windows limits. For example, reader Alan Gorski reports that when he increased a computer to 8GB, the program AutoCAD was able to open large drawing files without generating the "out of memory" errors he previously had seen. As Gorski notes, "AutoCAD has long used special memory management techniques since the DOS days to maximize use of available RAM."

There's a good chance your system is already using PAE. That's because Windows relies on the technology to support the security feature known as Data Execution Prevention (DEP). For more information about Windows and DEP, see my Top Story in the May 3, 2007, issue.

If a computer supports hardware-enforced DEP, then PAE is enabled as well. Here's how to check for it in Windows XP:

    * Step 1. Choose Start, Run.
    * Step 2. Type sysdm.cpl and press Enter.
    * Step 3. Click the Advanced tab. In the Performance box, click Settings and choose the Data Execution Prevention tab.
    * Step 4. Look for a status message at the bottom of the dialog box. If it indicates that your hardware does not support DEP, chances are PAE is not enabled.

To check your system's PAE status in Vista, do the following:

    * Step 1. Press Win+R to open the Run dialog box.
    * Step 2. Type SystemPropertiesDataExecutionPrevention and press Enter.
    * Step 3. If prompted by User Account Control, click Continue.
    * Step 4. If the status message at the bottom of the dialog box says your system supports DEP and the "Turn on" button is selected, then PAE is enabled as well.

If PAE is not already enabled on your system, here's how to activate it in Windows XP:

    * Step 1. Choose Start, Run.
    * Step 2. Type notepad c:\boot.ini and press Enter.
    * Step 3. Under the [operating systems] heading, look for a line that contains the /noexecute switch, which turns software DEP. For example, it may be /noexecute=optin, /noexecute=optout, or /noexecute=always on. Place the cursor directly after that switch and type a space followed by /pae. Save the file and reboot.

If you don't have DEP enabled on Vista (or you don't want it enabled), you can still activate PAE by following these steps:

    * Step 1. Click Start, type cmd.exe and press Ctrl+Shift+Enter.
    * Step 2. If prompted by User Account Control, click Continue. This opens a command prompt window with administrator privileges.
    * Step 3. At the prompt, type BCDEdit /set PAE ForceEnable and press Enter.

You can read more about PAE in this post on Microsoft's TechNet site.

Microsoft warns in another TechNet article that some drivers will not load if PAE is enabled. After you make this change, keep an eye on your system. If you have problems with drivers or your system starts acting up, remove the /pae switch from boot.ini in XP, or enter the following command line in an administrator command prompt in Vista:

BCDEdit /set PAE ForceDisable

Now, my comment...
I have DEP disabled (my choice), so I decided to use BCDEdit /set PAE ForceEnable command to enable PAE.
I restarted computer, and opened same 5 applications, I had opened before applying the above command:
Firefox, Thunderbird, Windows Explorer, Wordpad, and uTorrent.
These are Task Manager readings, regarding RAM ("Performance" tab):
BEFORE - total-2045; cached-1193; free-37; memory usage-55%
AFTER   - total-2045; cached- 1540; free-5; memory usage-39%
As you can see, "cached" part of RAM (which is the most important part; it's your "working" RAM), increased by almost 350MB, knocking "memory usage" down by 16%.

I hope, my conclusion is correct, and I still have to use the computer for a while to see the real effect.

I'm also very curious about the results from someone, who has 3, or 4GB of RAM installed on 32-bit system.
I have 2GB.

patio

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Re: Access more memory, even on a 32-bit system
« Reply #1 on: December 19, 2008, 07:10:40 PM »
Very nice review on this...
So because you're attempts at sabotaging my Vista install have fallen by the wayside you tempt me to do this on my benchtest machine with XP just to see the inevitable results .....
You have tweaked my interest...Onward i say ! !

                      ;)
" Anyone who goes to a psychiatrist should have his head examined. "

Broni

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Re: Access more memory, even on a 32-bit system
« Reply #2 on: December 19, 2008, 07:14:11 PM »
I won't rest until I screw one of your machines....that's my motto.....LOOOOOOOOOOOOOOOL

Broni

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Re: Access more memory, even on a 32-bit system
« Reply #3 on: December 19, 2008, 07:17:54 PM »
Joking aside, I'm basically waiting for my Firefox to reach 300-400MB of RAM usage.
Normally, at that point, FF becomes very slow, and I have to restart it.
Right now, FF is at 228MB.

Carbon Dudeoxide

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Re: Access more memory, even on a 32-bit system
« Reply #4 on: December 20, 2008, 04:26:29 AM »
Broni. Seen this?
http://www.computerhope.com/forum/index.php/topic,33321.0.html

Ever since that Config edit, all Firefox needs is a good minimize.

Calum

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Re: Access more memory, even on a 32-bit system
« Reply #5 on: December 20, 2008, 05:20:18 AM »
PAE is enabled by default on most systems anyway, to enable DEP.
I know on regular XP, using PAE does not enable more than 4GB of memory, no matter what.  Server 2003, however, could see all my 4GB of memory when I enabled this.
There's an interesting article on this somewhere, which points out that PAE is not the magic solution to break the 32 bit barrier, but I can't remember where it was.

Broni

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Re: Access more memory, even on a 32-bit system
« Reply #6 on: December 20, 2008, 05:41:47 PM »
Carbon
Minimizing FF doesn't work for me at all. Memory usage goes down just by a few MB.

Quote
I know on regular XP, using PAE does not enable more than 4GB of memory, no matter what.  Server 2003, however, could see all my 4GB of memory when I enabled this.
I understand, that there is no way to break 4GB barrier, but I'm just curious about being able to use more RAM inside 4GB. Like you said, you can see change with Server 2003.
PAE may be enabled by default, but I disabled DEP by choice, and when I checked on PAE, it was disabled as well.

Calum

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Re: Access more memory, even on a 32-bit system
« Reply #7 on: December 21, 2008, 04:06:50 AM »
Oh, I get you now.
What I mean is, on XP with my system, system properties reports 3.2GB of RAM.  With Server 2003, it reports 4GB.  That breaks the 4GB barrier by using 36-bit access - it sees 4Gb of RAM, plus 512Mb video RAM, plus the other memory allocated to devices.

Broni

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Re: Access more memory, even on a 32-bit system
« Reply #8 on: December 21, 2008, 11:45:32 AM »
That's interesting. Why do you think, it happens with Server 2003, but not XP?

Calum

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Re: Access more memory, even on a 32-bit system
« Reply #9 on: December 21, 2008, 12:28:19 PM »
http://www.computerhope.com/forum/index.php/topic,72489.msg473066.html#msg473066
killberb explains it there.
Apparently some drivers can have trouble with over 4GB of RAM available, so "home" 32 bit OSes cannot access more than 4Gb of RAM, period, because it's disabled.
Server OSes can use the extra 4 bits provided by PAE to access more memory.

Broni

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Re: Access more memory, even on a 32-bit system
« Reply #10 on: December 21, 2008, 01:54:37 PM »
I see...thanks.

macdad-



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    Re: Access more memory, even on a 32-bit system
    « Reply #11 on: December 26, 2008, 07:42:46 AM »
    does this work for all 32Bit versions of Windows(like NT and 2000) or is it just for XP and Vista?
    If you dont know DOS, you dont know Windows...

    Thats why Bill Gates created the Windows NT Family.

    BC_Programmer


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    Re: Access more memory, even on a 32-bit system
    « Reply #12 on: December 26, 2008, 08:44:58 AM »
    I don't think PAE support was available until XP was released.
    I was trying to dereference Null Pointers before it was cool.

    Broni

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    Re: Access more memory, even on a 32-bit system
    « Reply #13 on: December 26, 2008, 12:04:10 PM »
    According to M$, it's supported since 2000/NT: http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx, however the processor has to be Intel Pentium Pro and later.

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    Re: Access more memory, even on a 32-bit system
    « Reply #14 on: December 26, 2008, 12:05:39 PM »
    Alright- thanks Broni.... NT4 supported PAE?
    I was trying to dereference Null Pointers before it was cool.