does windows XP Pro 32bit support/use 4 gig of ram?

[myeq2b]

<p>see topic... may be upgradeing my motherboard/cpu and wanted to know that if using Windows XP Pro SP2 32bit, if it would detect and use 4 gig of ram? (i.e. 2x 2gig boards)</p><p>thanks in advance for info provided</p>

[Ama]

<p>Unfortunately i've heard it can only support 3gigs of ram.  Also heard weird rumors of it only supporting 2.5gigs, but how you can half a gig of ram leaves me scratching my head. </p>

[TSR-DanielH]

<p><cite>Amana wrote:</cite></p><blockquote><p>Unfortunately i've heard it can only support 3gigs of ram.  Also heard weird rumors of it only supporting 2.5gigs, but how you can half a gig of ram leaves me scratching my head. </p></blockquote><p>I believe the limit is actually a little over 3GB.  Keep in mind that the 3GB number includes the addressable memory on the graphics card as well.  That's probably why you heard the 2.5GB number.  That would be an accurate number for the RAM when running a 512mb graphics card.</p>

[Derrmerth2]

<p>Yes. It most certainly does. 32 bit = 4,294,967,296. Divide by 1.0234375 which is roughly the conversion factor bit to byte and you get 4,196,609,266. Which is very close to the exact amount of memory my 64-bit XP shows. Which is also nearly the exact amount of memory in a 4 gig kit. Microsoft even says it <a href="http://msdn.microsoft.com/en-us/library/aa366778.aspx#physical_memory_limits_windows_xp" target="_blank">if your bored</a>.</p><p>But what gives?</p><p>All the dry math shows that 32-bit XP supports <em>exactly </em>4 gigs of ram. You got a video card? Its got RAM. Some sound cards have RAM. RAM is also allocated to onboard devices as buffers for thier data. If you go in to Device manager and look at the resources tab under properties on some of your items under say system devices, you'll see a listing for a memory address. This (I believe) is RAM that is locked up for that device to use. In the end it is all RAM and it must also be addressed by Windows. It doesn't magically talk to your system.</p><p>So what happens is the actual amount you see inside Windows changes based on the total allocation of RAM in your system. This is why you hear weird rumors of varying amount supported. You got some crazy dual GPU card thats got 1.5 gigs on it, you will probably only have 2.5 gigs in your task manager in Windows. Windows is smart enough to allocate addressing to other devices, then when its done the remaining go to the OS itself. I <em>dare </em>you to try and limit the RAM your video card can access by some means of BIOS tampering. Odds are your card is not going to like you. So Windows lets it go first in the memory hand outs.</p><p>So the short of is, you have 4 gigs of addressing for everything inside that little box you play games on. Period. Once all your non-memory devices, ROMs and other bits and bobs have been given what they need for RAM addresses, Windows gets the rest. If your the smart kid in your class, I dragged up and <a href="http://www.codinghorror.com/blog/archives/000811.html" target="_blank">old page </a>going over this is more detail.</p><p>Opinion- It amazes me how much this exact question comes up. Which unless you have some more in depth understanding of this system, it is a mystery. People don't know/realize that RAM is RAM is RAM. It all must have a number for Windows to call and there are but so many numbers. Given the growth of computers in past years, 32-bit style OS has become a common tripping point for even home users. 4 gigs of system RAM is cheap. 6 gig kits are being sold for new i7 platforms on triple channel. Video cards with 512 megs or much more is pretty common. While the support from a lot of places in the area of software or drivers is great, the industry lacks that all together push to get the general user to switch over.</p><p>I advise any one who asks at this point in time to go 64-bit. Vista 64-but support is actually really good. Problems truly realted to 64-bit are few and far between. Lazy vendors are probably one of the biggest hurdels I run in to, as some simply dont support 64-bit or do so poorly, which dissuades users from making that jump. Its this terrible cycle of vendors saying they'll support when more people go 64-bit, and people saying they'll go 64-bit when more vendors support it. And round she goes.</p>

[Wingrider01]

<p><cite>Amana wrote:</cite></p><blockquote><p>Unfortunately i've heard it can only support 3gigs of ram.  Also heard weird rumors of it only supporting 2.5gigs, but how you can half a gig of ram leaves me scratching my head. </p></blockquote><p>Will support around 3.2. If you are ruinning XP SP2 this number will show 2.5, if you have SP3 it will show the correct number</p>

[Derrmerth2]

<p><cite>Wingrider01 wrote:</cite></p><blockquote><p>Will support around 3.2. If you are ruinning XP SP2 this number will show 2.5, if you have SP3 it will show the correct number</p></blockquote><p>Nope. It's 4. Always has been. Might want to take a peek at that post and the two links in it I threw together right above the post I quoted here.</p>

[Nionn]

<p>In case peeps refering to a link posted by <span ><strong>Derrmerth2</strong></span></p><p>are too lazy to scroll down:</p><ul><li>A 32 bit OS can only use 4GB of memory total, that means if you have 4GB of ram and your graphic card has 1GB of ram, you have a total of 5GB of memory.</li></ul> <ul><li>Out of that 5GB of memory, you can only use 4GB total. 1GB the graphic card will take up, so now the 32bit OS can only use 3GB.</li></ul> <ul><li>Enabling PAE, will limit to the OS to 2GB total. What PAE does is dedicate 2GB to OS and the other 2GB to anything other then the OS. Apparently some people don't understand how PAE works and think that some how it can magically make a 32bit XP use more then 4GB, which is impossible, a visual from MS itself might help. You can see it here: <a rel="nofollow" href="http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx" target="_blank">http://www.microsoft.com/whdc/syste...PAE/PAEdrv.mspx</a> </li></ul><p>Also FYI:  Vista 32bit can see only 3.5GB of ram total. The new sp1 only reports how much memory you have intalled, not how much memory you can use.</p>

[Wingrider01]

<p><cite>Derrmerth2 wrote:</cite></p><blockquote><p><cite>Wingrider01 wrote:</cite></p><blockquote><p>Will support around 3.2. If you are ruinning XP SP2 this number will show 2.5, if you have SP3 it will show the correct number</p></blockquote><p>Nope. It's 4. Always has been. Might want to take a peek at that post and the two links in it I threw together right above the post I quoted here.</p></blockquote><p>That show physical memory supported, not usable memory.</p><p>pretty good blog on technet</p><p><a href="http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx">http://blogs.technet.com/markrussin...21/3092070.aspx</a></p><p>for vista</p><p><a href="http://support.microsoft.com/kb/929605">http://support.microsoft.com/kb/929605</a></p><p>also depends if you are running with the /PAE</p><p><a href="http://support.microsoft.com/kb/291988">http://support.microsoft.com/kb/291988</a></p><p><a href="http://msdn.microsoft.com/en-us/library/aa366718(VS.85).aspx">http://msdn.microsoft.com/en-us/lib...718(VS.85).aspx</a></p>

[Derrmerth2]

<p><cite>Wingrider01 wrote:</cite></p><blockquote><p>That show physical memory supported, not usable memory.</p><p>pretty good blog on technet</p><p><a href="http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx">http://blogs.technet.com/markrussin...21/3092070.aspx</a></p></blockquote><p>I think we are on the same concept, maybe different wording. XP 32-bit does support 4 gigs, however what is actually useable in the Windows session is determined by what must first be allocated to other devices. This is to say if you had no video card, and could somehow run with out having to reserve ANY memory as buffers for onboard devices, you would see 4 gigs. In the article I left linked, it says the same thing under the 32-bit Client Effective Memory Limits section.</p><p>"While 4GB is the licensed limit for 32-bit client SKUs, the effective limit is actually lower and <strong>dependent on the system's chipset and connected devices</strong>. The reason is that the physical address map includes not only RAM, <strong>but device memory as well</strong>"</p><p>That was the point I was making. The amount of physcial RAM 32-bit can address is a full 4 gigs. However what you have when you log in to windows changes based on the devices you have connected, and the ranges that become reserved as I/O buffers for mainboard compents. Its a better way then the device manager example I made, but that article has a good picture of it, 4th graphic down in the 32-bit client section, white background pic. Its showing the ranges that are being withheld from Windows so that devices can lay claim to it for use. After the needs of devices are met for addresses, Windows gets to use the remaing addresses to assign to memory that it can use. Memory amounts greater then what it has remaing addresses for are simply truncated and not used, resulting in the less then 4 gigs useable.</p><p>So I think we are the same page, just saying it a different way perhaps.</p><p>EDIT - Rothaz said what I wanted to in a much quicker manner I think. Also made a good point about PAE. Tip o the hat to Rothaz.</p>