Windows XP supports 4GB of RAM, period.

Many people say that Windows XP doesn’t fully support 4GB of RAM. That’s not true, because Windows XP supports exactly 4GB of usuable RAM, by using PAE.

If you can’t use 4GB of RAM, and have PAE enabled, you have bought hardware that doesn’t support 4GB of RAM. There’s a KB entry, which details some of the problems. If you want to use the full 4GB, buy better hardware.

39 Comments

  1. Craig:

    I do not agree with your statement “If you can’t use 4GB of RAM, and have PAE enabled, you have bought hardware that doesn’t support 4GB of RAM”…

    My BIOS reports 4GB RAM as does Intel Desktop Control utility (run from Windows). I have enabled PAE and the /3GB switch and combinations of the two but the amount of RAM Windows reports does not change by 1 byte.

    The Microsoft KB article explains the symptoms nicely but is about as much help as an ashtray on a motorcycle.

  2. neil@anon.penet.fi:

    The grandparent is omitting the fact that many hardware devices occupy a portion of the physical address space. You’re very unlikely to have the full 4GB available to you with XP SP2 even with PAE enabled (which is the default by the way.)

  3. wizualizacje:

    Thanks for the info.

  4. djswarm:

    Approximately 0.5 gb of ram is resevered by the system for the PCI-e bus, shared video ram and what not, plus drivers often eat up some of it. MS went from reporting total RAM to reporting available RAM so you’ll never see more than about 3.5 gb on a 4 gb system no matter what switches you use.

    Some chipsets will let you tweek this number, tweek at your own risk, but on the whole XP is just being honest for once about what is there.

    /PAE introduces some issues of its own since most client drivers are written without any expectation of /PAE. See the MS KB on XP and /PAE for details.

    Personally I would say if you need gobs of memory you really should be running 2003 x64 or 2008 (xp x64 sucks) as they handel 4+ gb way more efficiently. Or you could use a real OS like RHEL 5.1 x64 :P

    XP is rumored to not really use the second GB very effectively. I say rumored cause I haven’t had the need to verify that, but the people who told me were uber geeks I trust to know such things.

  5. Computer Guy:

    If XP is reporting what ram I can actually use, why does a single stick of 512, say 512?
    Two 1Gb sticks say 2Gb.

    I think you have a flaw in your logic, and no, Red Hat 5 is not the answer. ( far from it )

    If you must use windows, and really need lots of memory, Windows XP x64 is the way to go.
    But, if you are going to have lots of memory, do yourself a favor, get a RAID card.

    Here is a box I built a few months ago, and it is SCREAMING fast
    Intel MB
    Xeon dual-core 2.4
    8Gb PC6400
    XP x64
    3 SATA II drives RAID-5 ( pci adapter card )
    PCI-x16 512Mb video

  6. so yeah...:

    ^ The problem is that XP32 has a 4GB address space – it can only address 2^32 addresses. These addresses are taken up not just by your main system RAM, but also graphics card RAM and other things.

    So if you have 2 GB of RAM you don’t have any problems because XP32 can address the 2GB of your main RAM as well as perhaps 512MB of video memory and some amount of other addresses used for other stuff. The total of all these addresses is less than 2^32.

    With 4GB of RAM in your computer, the total number of addresses will be greater than 2^32, and some portion of your main RAM will be inaccessible.

  7. Ernest:

    I have 4 gigs of ram, and an XP/Vista32 dual boot system. I have PAE enabled, but XP still only sees 2 gb of ram, and vista sees all 4 gb. So here we are. :(

  8. Brent Williams:

    Just installed 4 gigs of ram into my XP system. (Had 2 gigs – saw all of it, upgraded to 4 gigs) Bios sees all 4 gigs but system only sees 2.75 gigs. I have two 512 meg 8800 GT’s running in SLI. My friends computer is practically identical except he only has 1 8800 GT and his available ram is 3.3 gigs.

    Are my video cards sucking up a gig of my available ram? Seems odd. I’m running an nVidia 680i SLi motherboard, Intel QX6850 Extreme Quad Core, overclocked to 3.66, dual 8800 GT’s in SLi mode, 2 SATA 750 gig drives in RAID 0 mode (1.36T stripe) and 4 gigs (4 x 1 gig) Corsair Dominator DDR2 ram running at 2.2 volts (1066 MGz overclocked). Was it worth buying the extra 2 gigs or what? If I’m only seeing an extra 750 megs of ram out of it?

  9. nick:

    I also have 4gb ram installed on my mobo, xp pro only sees 2.5gb with my dual 7900gto’s 512 cards.
    i have a msi p6n 680i mobo, with 4x 1gb corsair value select 667. bios and every other program sees the 4 sticks, apart from xp and vista ultimate 32(dual boot).

  10. KJ:

    Video RAM is included in Windows’s address space. So, of you have 1024 MB of video RAM, Windows will have only 3GB of address space left for system RAM. An additional 500MB of address space is usually needed for other hardware, leaving you with 2.5GB of available RAM.

  11. Steven Kirkland:

    I believe the greatest problem in the conveyance of understanding is in the explanation of Windows XP and memory. Aside from ≈ 500MB of memory map addressing for BIOS/drivers/other basic hardware, you also lose part of that memory addressing to video ram. Simply put, you’re not losing ram to your system requiring it, XP worked for years on 128MB using the same 4GB addressing for hardware, you’re losing the upper portions of `memory addressing` space starting at 4GB and working it’s way downwards dependent upon how much is required for windows to use your goodies.

  12. Charles:

    This “issue” is not a Windows XP issue, but a 32-bit system issue. As said above, 32-bit means a maximum of 2^32 bytes of addresses. And these addresses does not mean it should be only your RAM addresses, but your hole computer hardware addresses.

    So, again, if you have 4GB of RAM, it won’t use all of it, because the system requires some other addresses (like those 512MB from your video memory), and then winXP 32-bit just won’t be able to access your hole RAM memory addresses.

    In 64-bit systems, 2^64 = 128GB. So you can use your, let’s say, 8GB of RAM plus a dual 512MB nvidia cards and there will still be plenty of addresses for the operating system use.

  13. andrew:

    where can i find this pae on my system please.
    thanks in advance

  14. David Reis:

    Enable 4GB tuning and PAE.

    Just read:
    http://www.cadforum.cz/cadforum_en/qaID.asp?tip=5551
    If you want to make accessible 3GB RAM for your CAD applications in Windows Vista, use the BCDedit.exe tool (Boot Configuration Data Editor). The 3GB RAM mode can be enabled by the command:

    bcdedit /set IncreaseUserVa 3072

    and disabled by the command:

    bcdedit /deletevalue IncreaseUserVa

    Run this command from a command window with Administrator priviledge – i.e. (in the Start menu) type CMD and press Ctrl+Shift+Enter, or select “Command Prompt” (Accessories), right-click on it and choose “Run as Administrator”.

    You could download and install VistaBootPRO 3.3 and enable Physical Extension Addressing on windows vista too.

    But on taskmgr you will only see 3gb available.

  15. David:

    Although thi is an old issue, i still see fairly recent comments-questions that clerly show that sometimes the answer to issue is not properly understood.

    This is the same explenation through an over simplified analogy:
    To people to be able to recieve mail thy must have an address that will enable the post office to know to where to direct it to. Lets say for this analogy that for technical reasons the post office can only allocate addresses in the form of two digit numbers – that means 0-99 (covers 100 houses). If the region holds 120 houses, 30 of which have high priority to mail what will happen then? Those 30 will recieve an address and will have mail delivered to them, from the other 90 houses only 70 of them can get addresses, all the rest wont be able to get mail(they have no address).

    In terms of the memory mapping – 2^32 = 4GB is the number of addresses available. The system resources (System ROM, APIC(s), Integrated PCI devices – such as network connectors and SCSI controllers, Graphics card and more) have priority (otherwise they wont be accessible) and the rest – Less then 4GB- is left for the RAM.
    Now its not that the remainder is used for anything\eaten up and so on – there simply not mapped, which means they have no address that can be used to refer to them for read\write operations.

  16. Johnny Q:

    Charles, 2^64 = 2,199,023,255,552GB, not 128.

  17. lurking:

    lukas u must read all…
    1. go to ur own link http://en.wikipedia.org/wiki/Physical_Address_Extension
    2. go to this http://en.wikipedia.org/wiki/Physical_Address_Extension#cite_note-8
    3. klik the link http://msdn2.microsoft.com/en-us/library/aa366796(VS.85).aspx
    4. and then klik this http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx

    read all will ya before u post

  18. Alex:

    The question is what happens to that half-gig at the 4GB top?

    Is it used in any way for said device drivers? If it is actually utilized to at least some extent, that should calm many folks.

  19. tommynatl:

    So , I guess if you didnt have the 4gb of ram, then you would have even less ram to work with after xp utilizes what it needs.
    Total Physical Ram = 4GB
    Windows XP 32bit = -.5GB ( 500MB )
    2 X 512mb Video on SLI= -1GB
    ______
    Total left 2.5GB

    Is this correct ??

  20. nardofor:

    Why people keep on posting stupid things like the addressing space is 2^32 and they don’t give a read to the link posted by the author which clearly explains PAE extends it to 2^36 by using page tables and 36 bit registers?
    Why other people keep on telling their OS says it has only 2.7 or 3.3 GB and they don’t give a read first to the KB article posted by the author which explains why?
    This would really make things easier

  21. d00d:

    Why are people getting upset at wrong info from 2 years ago?

  22. finky:

    “Why are people getting upset at wrong info from 2 years ago?”

    It’s important that people correct these questions so people don’t read wrong info and spread it. This came up as one of the first searches in Google. If you took a moment to think before opening your pie hole you wouldn’t have posted that. Keep doing it, you’ll go far.

  23. mdmx:

    — tommynatl wrote —
    So , I guess if you didnt have the 4gb of ram, then you would have even less ram to work with after xp utilizes what it needs.
    Total Physical Ram = 4GB
    Windows XP 32bit = -.5GB ( 500MB )
    2 X 512mb Video on SLI= -1GB

    Is this correct ??

    No this is not correct. Windows and video cards doesn’t consume any memory, they consume addresses which are also used to access the memory.

    So to keep this simple, if you have 4GB of ram and 1.5GB of addresses are used for video cards and other stuff, then the 1.5GB of your actual ram is NOT used in ANY way. And there is nothing you can do about it in normal 32bit desktop computer. So don’t buy it in the first place, buy 2x1GP + 2x512MB (3GB) instead. With 512MB video memory 3GB RAM can be accessed so you don’t lose any. If you have total 1GB of video ram then your system can only access 2.5GB of ram memory.

    PAE switch requires application support. And supporting applications are very very rare, stuff like autocad and maybe some servers. In normal desktop use, PAE does NO GOOD, and may cause problems, so do not use it.

  24. tommynatl:

    I would gladly jump on the 64bit OS bandwagon if I felt it would be supported.

  25. Crabman:

    Hello, just to upset the apple cart regarding this 4Gb issue. I would just like to know if I install 4gb of ram into XP 32 bit – will it cause errors or just happily carry on ignoring the extra. I dont care that it wont show etc, I just dont want the system to be unstable.

    Thanks

  26. Lukas Beeler:

    Crabman,

    Installing more memory will not make your OS unstable in any way.

  27. Crabman:

    Thanks for the quick response, cheers

  28. Oreo27:

    Hey guys. I’ve recently installed 4GB of RAM in my 32 bit Windows XP. I have a 1 GB GeForce 9500 vid card. There was an option for memory mapping in my mobo which I’ve disabled and I’m getting confusing results from different sources. Let me explain, In my O.S. and my BIOS it shows 3.25 GB of RAM installed although in cpu-z it shows 4096 or the actual 4GB. From the explanations all over the Internet, I’ve gathered that a 1 GB video card takes up 1 GB of address space, and other hardware takes up about 512 MB. So 4GB RAM , 1 GB Vid Card, 512 MB for others is basically 1.5 GB for my other hardware and 2.5 GB for my RAM, how come it’s showing 3.25 GB?

  29. darktemplar242:

    he tells true BUT
    MANY PERSONS DONT THINK ABOUT VBIDEO CARD MEMORY,
    ITS TAKING ON THE 4GB
    SO A 1GB CARD WITH 3X 1GB RAM
    IS 4GB,NO MORE,PERIOD
    YOU CAN USE 2X4 GB RAM WITH A 1GB CARD,
    BUT WINDOWS WILL ONLY TAKE 3GB!

  30. Bujar:

    Guys, you really messed up my brain now.

    I’m using Dell Vostro 1510 with 2GB RAM. Since last month i’m planing to upgrade it’s RAM memory to 4GB but if I want to install 64bit Windows XP there are no drivers available supporting 64bit XP. Vista is not a good choice for me and I don’t know what to do. Does anyone have a concrete answer ?

  31. Darren:

    Hi i upgraded the ram in my pc from 2 x 512 ddr1 to 2 x 1gb ddr2 but bios and windows only shows 1gb (2×512)motherboard is pc chips p23g any help thanks.

  32. Steve:

    OK windows xp is a 32 bit system. so there for it will only read up to 3.75 GB of RAM. There is a file you have to edit for it to read more.
    Windows Vista 32 bit only reads 4 GB of RAM.
    And any 64BIt will read more than 8 GB of RAM. check your motherboard or pc specs on the max ram your pc board can handle. anymore than what it can handle will fry it. have a nice day.

  33. wizualizacje:

    In practice it’s work only with 3GSwitch

  34. Krishna:

    Hi Steve

    I have installed 4GB of ram in my system but its still showing me only 2Gb.How can i utilze complete 4 GB of Ram With Windows Xp 32 bit Service pack2. you have mentioned that we need to edit the some file to utilize.
    Can you please let us know which is the file and where we can find it.

  35. bandsxbands:

    It’s interesting to see just how permeant virtual memory has become in our every day lives. It seems like everywhere I turn, I see something with a card slot or USB port . I guess it makes sense though, considering how cheap memory has become as of late…Gahhhhh… I shouldn’t be moaning and groaning. I can’t make it through a day without my R4 / R4i!(Posted using FPost for R4i Nintendo DS.)

  36. Larry Miller:

    PAE will do nothing for you in XP since SP2.

    XP cannot access all of 4GB because a portion of this address space must be shared with memory mapped hardware devices which always have priority. Wherever this conflict occurs a portion of RAM will be unavailable. Most modern motherboards allow the remapping of this conflicting RAM to an address above the 4GB mark. PAE was designed to allow access to RAM above the 4GB mark. On most server systems this permits almost all of the 4GB to be accessible.

    But there is a downside to this, and a rather serious on at that. Many device drivers for popular hardware devices fail badly in such an environment. Starting with SP2, XP will simply ignore any RAM above the 4GB mark, thus avoiding the problem. PAE does nothing useful in XP. It is maintained primarily as a convenience to the developers of device drivers for testing purposes.

  37. rob:

    Nonsense. 32-bit windows can utilize more than 4GB of physical RAM. Period.
    See http://pcgamingtips.blogspot.com/2010/04/yes-virginia-32-bit-windows-can-use.html for a simplified view, or read and understand the material in Russinovich/Solomon windows internals. Moot for sure at this point, since the reasons to stay 32-bit in the consumer space are long remedied.

  38. Lukas Beeler:

    rob, Server editions can use more in specific circumstances and for specific applications, but XP can’t. Of course you can start hacking files (and violate your license agreement), but that’s another topic.

  39. Rob:

    Sorry, Lukas, you are indeed still incorrect.

    No ‘hacking files’ is needed to do this on a standard, legal, 32-bit non-server version of Windows. See the picture in the link I referenced earlier. This product uses its own Kernel driver, nothing more. Semantically, if one asks if ‘Windows’ 32-bit can use more than 4GB, they must include applications running under Windows. The server versions of 32-bit Windows do that – and so do the non-server version when using an approprately coded driver.

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