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Windows XP RAM recognition

Posted on 2006-11-12
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I have a new Dell Precision 690 workstation with a Core Duo Xeon 5160. The BIOS shows the two cores and the 4 GB of RAM ( 4 x 1 GB sticks). In "View System Information" General Tab it notes only 1 Xeon 5160 processor and exactly 3 GB RAM. Should Windows recognize both processors and all 4 GB of RAM? If so, what needs to be fixed to do it?
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Question by:MarkDSegal
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by:phototropic
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It is a known issue in XP: the BIOS sees all the RAM, but Windows under reports it:

http://support.microsoft.com/?id=888137
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by:phototropic
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by:MarkDSegal
ID: 17926549
Thanks for the references. They don't tell me what the implications of this limitation are and how to work around it so I can access 4 GB RAM. Perhaps it is not possible? I checked the boot.ini file and it looks like this:

[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect

However, in "View System Information" under the indication of 3GB RAM, it says "Physical Address Extension", which would appear to indicate that PAE is enabled - but PAE or 3GB do not appear at the end of that string in the boot.ini file. So it all remains a bit of a mystery to me.
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by:phototropic
ID: 17926722
Google is full of forums on this topic.  It appears that no amount of fiddling about with your boot.ini file (/PAE switch; /3Gb switch; etc.) will render XP capable of "seeing" all 4 Gb.
Take a look at this:

http://www.experts-exchange.com/Operating_Systems/WinXP/Q_21691179.html?query=WinXP+4Gb+RAM&clearTAFilter=true

If you upgrade to 64-bit, XP can see 128Gb...
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by:phototropic
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by:MarkDSegal
ID: 17926785
Thanks. I'm starting to get the picture. I was getting concerned that something was wrong with the system install on my computer, but now I see this is normal. Anyhow, 3GB of virtual memory will probably handle heavy duty stuff like Photoshop quite well.
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by:garycase
ID: 17927147
"... Should Windows recognize both processors and all 4 GB of RAM? " ==>  The discussion correctly notes that you won't be able to use all 4GB of your installed RAM  [the system does "see" it ... it's simply not able to use it, because there is only 4GB of address space available, so the highest addresses must be used for other system-related addresses ==> in fact, if you have the correct hardware support for it, and use the /PAE switch, you MAY be able to use it all (but I don't recommend using /PAE anyhow, as it adds a layer of address translation to ALL memory references)].

But nothing was said above about the first part of your question ("... Should Windows recognize both processors ...") ==>  Windows should correctly report one Xeon, but it should show 2 cores.   Go to Task Manager (Ctrl-Alt-Del) and click on the Performance tab.   Be sure "View" is set for "one graph per CPU" ==> and observe how many panes there are for CPU Usage History.  (there should be 2)

If that's not what you're seeing, go to Device Manager, and expand "Computer" (click the "+" sign).   This will show what HAL (Hardware Abstraction Layer) is installed for your copy of XP.   It should read "ACPI Multiprocessor PC"

Back to the memory question for a bit:  There are MANY misconceptions about XP's management of memory --> including quite a few incorrect answers here at EE (e.g. question #Q_21691179 referenced above has several incorrect statements).   Just be aware that there are several reserved memory addresses that MUST be assigned within the 4GB address space ... and that the consequence of this is that 4GB of RAM cannot be utilized with a 32-bit address space.   If you research this yourself, you'll find the following is true:

(a)  XP systems with 4GB of memory "see" anywhere from the low 2+ GB up to about 3.5GB.   The upper end of the address space is used for a variety of reserved items -- BIOS shadowing, AGP aperture, I/O addresses, video shadowing, etc. -- and for these reasons systems with 4GB of installed memory never report a full 4GB of available memory.

(b)  XP restricts the memory allocated to individual processes to 2GB, but uses any memory above for system processes that would have occupied lower memory if the system had 2GB or less of memory;  the /3GB switch will alter that balance -- but has NOTHING to do with "seeing" more memory in systems with 4GB of memory (it simply increases the virtual address space allocated for individual processes);

(c)  the /PAE switch, on systems that have chipset, CPU, and OS support for it, will allow you to use all of 4GB (or even more if the motherboard supports it) by remapping the additional memory above the 4GB barrier imposed by 32-bit addressing (it does this by adding 4-bits to the address registers and dynamically managing the mappings);
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by:MarkDSegal
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Thanks Gary. Re your point (c) above - eventhough the PAE switch does what you say, am I correct to understand from your first paragraph that you do not recommend activating it?
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by:garycase
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Yes ... the extra 4 bits it adds when managing memory are managed by the CPU => not the memory controller.   This adds a bit of extra overhead whenever the memory page address changes.  It's very minor ... but it IS overhead.   It's worth trying if you want ... but the difference between 3GB and 4GB of memory is very minor (remember, no process gets over 2GB anyway unless you also use the /3GB switch), and it's not clear the benefit of the extra memory offsets the added overhead.   Just depends on the application.   On motherboards that support larger amounts of memory it's probably worthwhile ... but probably not with 4GB.
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by:MarkDSegal
ID: 17927276
Thanks Gary. The main application at issue here is Photoshop CS2 which is a real RAM hog. I'll see how this new computer handles Photoshop before experimenting with this stuff. I read elsewhere that activating these features can interfere with some driver performance. But if I do activate, it seems from the foregoing there are two things that need to be added (1) the PAE function and (2) the /3GB function. Is that correct? If so, where? (As I mentioned, at present my Windows System Information suggests PAE is active but there is no mention of PAE on the operating system string in the Boot.ini. )
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by:garycase
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You have to add the switches at the end of the BOOT.INI line for the OS.  Right-click on My Computer; select Properties; click the Advanced tab; click on Settings under Startup and Recovery; then click on the Edit button.   In the line under the [operating systems] section that defines your XP system ("multi(0) ... ") add the /PAE and /3GB switches.   It won't hurt anything to try these ... you can simply delete them if you don't like the impact they have on the system :-)
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by:MarkDSegal
ID: 17927664
Thanks Gary - I'll keep this on file and try it if I think the system seems starved for memory once I get Photoshop loaded and tested. I'm just getting the system converted from my Dell 8200 - takes time.
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by:phototropic
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MarkDSegal,

Good morning! (It's 8.30am here in the UK)...Garycase seems to have covered this whole 4Gb/WinXP topic very comprehensively...

As regards Photoshop, take a look at this re: RAM usage:

http://www.adobe.com/support/techdocs/320005.html

As you can see, Adobe recommend applying the /3Gb switch, but point out that it may not work with all computers (? Which ones?  Why not? ). The article also points out that RAM allocation can be adjusted by the user - they suggest in 5% increments.  The default is 55% for Windows (and a whopping 70% for Macs!)

There are many forums which discuss PS and RAM usage, but the bottom line appears to be that the os will dictate how much RAM is available to each application, so that the difference between 3Gb and 4Gb may very well be simply that you can multitask and run several programs simultaneously with PS, rather than a difference in PS performance...
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by:MarkDSegal
ID: 17929677
Phototropic, thanks. I am very familiar with that Adobe article. Obviously, there are so many computers and OS configurations out there that they cannot address every situation and expect to get it right for everyone, so they need to generalise a bit. RAM allocation for use of Photoshop is a completely different issue from the amount of RAM that the O/S will recognize and utilize. The amount of RAM at which Photoshop operates most efficiently depends on the size of the image being processed. As you probably know, especially working in 16-bit mode, layered images can be several hundred MB each, if not more. Adobe typically recommends that the amount of RAM accessible to Photoshop should be about 5 times the file size of the image; hence Photoshop should be able to access say one GB of RAM if it is working a 200 MB image file. If it cannot access all the RAM it needs, it then uses the SWAP space on the hard drive (one should have swap spacde on a separate hard drive from the C drive), and this bogs down efficiency. So when you see the efficiency indicator dropping below 100%, you know the swap space is being used, and it is time to revisit the RAM allocation. The default 55% is recommended because the O/S needs RAM for other things apart from Photoshop - of course - so if it is set too high, it can actually drag Photoshop performance downward because background processes are being impacted. This is why Adobe generally recommends an upper limit of about 75% for Photoshop; hence the user should work between say 55% and 75% in a Windows 32 bit environment to optimize the RAM reserved for Photoshop. Photoshop can only access 2GB of RAM unless it is scripted for 3 GB access, and they say how to do this. But as I said, this is separate issue from how Windows IN GENERAL AND FOR ALL PROGRAMS uses RAM.
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by:MarkDSegal
ID: 18095777
Actually, this should not be abandoned. I have a supplementary question along the same lines. The system does recognize the total RAM and the dual core processor, so there is not a hardware issue. But the system could be addressing more than 2GB of RAM (because I am using Windows XP Professional) if I activate the "3Gb switch". This is supposed to be done by adding a command to the boot.ini file, but it isn't clear to me whether the string I have in my boot.ini file allows this. This string, reproduced below is somewhat different from samples I have seen in instructions provided by Adobe and Microsoft. Also, not clear whether I need to add both the PAE and the 3GB or if only adding the 3GB is enough. Before trying this I would appreciate confirmation from Gary or another one of your experts whether adding either or both of these to the command line below will at least NOT mess-up my computer and perhaps help.


multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect

Mark Segal
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by:garycase
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That string is exactly where you would add the /3GB and /PAE options (either or both).  The /3GB switch has no effect on how much memory the system can address ... it only changes the maximum amount of virtual space that a single process can be assigned (from 2GB to 3GB).   The /PAE switch will enable the address extensions that, IF your motherboard and CPU support it, will allow addressing memory above the 4GB limit imposed by a 32 bit address space.

You will NOT "mess up" your computer by trying either or both switches :-)
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by:MarkDSegal
ID: 18098470
Thanks Gary - that's of some comfort, but now the question is "will it be useful?" I'll explain. As you may know, when using Photoshop there is an efficiency indicator at the bottom left of the window. If a Photoshop process exceeds the RAM assigned to Photoshop and/or available to the program in total, the efficiency drops below 100%, which means that the scratch disk is being deployed. The scratch disk is on a second hard drive, which even spinning at 10K RPM still slows execution very considerably. When setting up Photoshop preferences, under "Memory and Image Cache" Preference, it tells me that there is say 1756 MB available to Photoshop, so if I give Photoshop 75% of that, it has 1317 MB. One would hope that is enough, but it isn't always. Giving Photoshop more than 75% is a bad idea because then other functions that need to run simultaneously to support Photoshop get RAM-starved and things grind-down - the opposite of what one is aiming for. I believe the 1756 MB initially available is the amount Photoshop can use after the basic needs of the O/S are spoken for; hence even with 4000 MB of installed RAM, if the system can only access 2000 MB and the O/S needs say 250 MB, that would explain why Photoshop only has a maximum of 1756 assignable, of which one does not assign the full amount as explained. So, now to the bottom line: I am wondering whether setting that RAM switch to 3GB will give me more leeway to increase Photoshop's RAM allocation or otherwise keep more the processing task in RAM rather than the scratch disk, while not starving the system's cooperating functions, or would it have no such effect?

As a "by the way", I've been told by MacIntosh afficiados that Mac O/S 10 is a much more efficient allocator of system resouces than Windows XP, hence these constraints on RAM and frequent recourse to the scratch disk would not happen nearly so much. Any views on that? (OK, I'm a Windows user, so I'm not trying to ignite a Mac vs PC slug-fest; this is just out of curiosity in light of the contentions one hears!)
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by:garycase
ID: 18098595
->  There are fundamentally two issues here:  (1)  How much memory your system "sees" (which I believe is exactly 3GB); and (2)  how much it can allocate to Photoshop.

-->  I would first add the /PAE switch to the BOOT.INI file and note whether or not this changes the amount of memory displayed as available [right-click on My Computer; select Properties; and see what that reports --> both before and after the /PAE switch is added].   IF it makes a difference, then you can leave it enabled.   If not, I would remove that switch.

-->  I would then add the /3GB switch and see if this allows Photoshop to be allocated more memory (it DOES allow XP to assign up to a 3GB virtual space ... but exactly what interaction this has with the way Photoshop determines its allocation I don't know).


... By the way:

->  You never did answer my question r.e. your HAL => What does your system show for that?

->  I don't doubt that Mac OS-10 does a better job of managing memory.   Macs have always had a linear address space (unlike the early X86 CPU's) and have also been better focused on large address space applications (graphics, photography, etc.).   But I'm not a "Mac person" ... so I don't know the specifics.
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by:MarkDSegal
ID: 18098739
Thanks Gary - yes, HAL is ACPI Multiprocessor PC.

Now, on the PAE switch, further back you did not recommend it because it adds "overhead" - did you change your recommendation in light of my more specific re-statement of the issue regarding Photoshop? Thanks for the suggestions. I can see there is some experimentation to do here.
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garycase earned 250 total points
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The overhead associated with /PAE is fairly small => there is some support in the chipset/CPU that helps;  so it really depends on how much benefit the system gains from the added memory.   Since Photoshop is so memory intensive, it may very well be a case where it's worthwhile => even ONE disk access (which takes many thousand microseconds) can offset a lot of microseconds of memory access penalties.   As for the /3GB switch, that has nothing to do with how the memory is accessed => it simply increases the maximum address space XP will allocate to a single process.   ... so yes, you need to do a bit of experimentation to confirm whether or not these switches will be beneficial in your specific case.
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by:MarkDSegal
ID: 18191804
No, I believe we have exhausted this thread, and I appreciated the help

Cheers,

Mark
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by:garycase
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Don't forget to close the question (Accept an answer, or Split the points).   ... and Merry Christmas !!
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