Windows XP recognize 4 Gb ram ? ( 3 Views )

1. If I buy 4 Gb ....what's happend with windows ? does it recognize or not ?
   
   
   (bugra, Thailand)


2. win xp pro should recognize 4gbs
   
   
   (hackan, Netherlands Antilles)


3. Quote:

   Originally Posted by amd ati FO SHO win xp pro should recognize 4gbs

   and not Home version ? Why ?
   
   
   (ali, Heard Island and Mcdonald Islands)


4. Well, there's no point to installing 4GB in WinXP, here's why: Windows allocates memory to PCI/PCI-E/AGP devices in the 4GB range. In other words, you can install 4GB, but you may see anything from 2.5-3.5GB even though the BIOS says 4096MB. Windows reserves parts of that uppper memory register for other devices. Unless you have a non-Windows 32-bit system or WinXP Pro x64, there's absolutely NO benefit to 4GB RAM. Physical Address Extentsion (PAE) allows the memory to be remapped above 4GB so that all 4GB can be accessed by drivers and programs. However, some drivers have issues with PAE and can fail. I repeat: 4GB of RAM is not worth it in WinXP 32-bit, Pro or Home! 2GB is the new 1GB, you'll be fine with two gigs for now.
   
   
   (serif, Bermuda)


5. XP Home & Pro support an address range up to 4 GB for physical memory addresses. Those addresses are sub-divided to manage both the PCI memory address range (MMIO) and physical user memory (RAM). Starting at the top of the address range, the BIOS takes roughly the first 512K of the address range. Next, your graphics card(s) need addresses for at least the amount of memory on them. Then, other things like IO cards, networking, PCI-e, bus bridges, etc. take what they need. The net result is that a 32-bit OS on an x86-based pc may allocate 512M~1G (or more) for the MMIO range BEFORE any RAM addresses are allocated.
   
   Say for example, you have (2) 512M video cards. All of that memory needs to be addressed before your RAM can be. Add in everything else I mentioned above and you'll probably wind up with roughly 2.5G of address range left for your RAM.
   
   From what I've seen, with a 256M video card, you'll wind up with 3-3.4G of your RAM being able to be addressed. Hence the number that is reported in Windows.
   
   XP Pro x64 and Vista, being 64-bit OS's, resolve this limitation by using a 64-bit addressing scheme (not PAE - PAE is only used on win32) to re-map MMIO above the top of the physical memory....as long as your 64-bit capable system isn't using a 32-bit chipset... The Intel 925 is a good example where, even with x64 installed, you still wind up having only 3.4G available because it can't use the 64-bit addressing scheme.
   
   
   (bahar, United Arab Emirates)


6. Oops...sorry Sovereign, looks like you type faster than I do ;)
   
   
   (ümüþ, Falkland Islands (Malvinas))


7. try something.. add the /NOLOWMEM switch to the boot.ini, should move all the pci memory addresses to >4gb ;)
   
   
   (mehmet, Jamaica)


8. Quote:

   Originally Posted by (cf)Eclipse try something.. add the /NOLOWMEM switch to the boot.ini, should move all the pci memory addresses to >4gb ;)

   Does that impact performance?
   
   In any case, the statements about memory addressing in 32bit Windows XP are true. On my system I get 2.5GB of memory and that's it. Though I generally run Windows XP Professional x64 Edition and it sees all 4GB just fine. The only thing I use XP 32bit for is video capture. I use x64 Edition for everything else.
   
   
   (Bünyamin, Nigeria)


9. Quote:

   Originally Posted by Dan_D Does that impact performance?

   not from what i can tell. i should run some tests though
   
   and yeah, i use xp-64 as well.. ;)
   edit: but the switch should work with xp-32
   
   
   (serap, Somalia)


10. I thought the switch was "/pae".... :confused:
    
    
    (didem, Bahrain)


11. Windows doesn't reserve the memory; the device requests that the system reserve the memory. The amount of usable physical memory that will fit in the address space will depend on what peripherals you have installed and how much they're configured to map.
    
    If you've got a fancy graphics card with a ton of memory and a big aperture, then yeah; you'll take that size out of your address space. If your application doesn't need such a card, then get a cheaper one with less video memory and you'll see more of your pyhsical memory in the address space.
    
    Mapping the card memory happens on any OS; it's not a Windows-specific issue. I don't see how a non-Windows OS would work around it. You've run into a hardware limitation, not a software limitation.
    
    If you're using a newer processor with DEP, or a ccNUMA-based AMD system, you'll probably have /PAE on anyway.
    
    By the way, I've posted an essay with details and references about this issue over in the Operating Systems forum.
    
    
    (burçin, Malaysia)


12. Quote:

    Originally Posted by Sovereign I thought the switch was "/pae".... :confused:

    You're right man, it is - to enable PAE if it isn't already enabled.
    
    Typically PAE is enabled by default when the processor supports PAE and the computer has more than 4 GB of physical memory.
    
    The /nolowmem switch loads the operating system, device drivers, and all applications into addresses above the 4 GB boundary, and directs Windows to allocate all memory pools at addresses above the 4 GB boundary. The parameter is valid only when PAE is enabled on the system, that is, the PAE version of the Windows kernel is loaded.
    
    --
    
    The Microsoft white paper can be found here: http://www.microsoft.com/whdc/system...AE/PAEdrv.mspx
    
    
    (kuþ, Russian Federation)


13. i've found that /PAE doesn't really do the job from my relatively limited testing :(
    
    
    (sonnur, Bhutan)


14. Quote:

    Originally Posted by (cf)Eclipse i've found that /PAE doesn't really do the job from my relatively limited testing :(

    Which job is that?
    
    
    (baran, Guinea-Bissau)


15. Quote:

    Originally Posted by mikeblas Which job is that?

    getting all 4gb to show.
    
    
    (büþra, France)


16. Quote:

    Originally Posted by (cf)Eclipse getting all 4gb to show.

    Everything has to cooperate. Is your BIOS set to allow the mapping? Does your motherboard support it? Does the version of chipset drivers you're using?
    
    
    (sýtký , Seychelles)


17. i'll have to check when i get home, but if i do not have the PAE kernel loaded is it going to be a huge PITA to load it? does it require a fresh install or can i upgrade to it with relative ease?
    
    i am asking because i have a relatively new AMD XP X2 system with 2GB of ram right now that is running windows XP pro 32 bit. but i am getting fairly heavy into virtualization on this machine and am looking to upgrade my disks and/or memory to help with performance. i'm trying to figure out where my money is best spent.
    
    
    (LEYLA, Chile)


18. There's not a seperate "PAE kernel". /PAE is a boot option.
    
    There's technical documentation for /PAE in the DDK on MSDN. There's other docs for /PAE here and here.
    
    You'll find that your AMD machine probably already has PAE enabled because it probably has DEP turned on by default. You can read technical documentation for DEP on MSDN. Non-technical docs are here.
    
    As aways, where your money should be spent depends on your workload. But if you're virtualizing to lots of sessions, I would think you'd want to increase memory first.
    
    
    (nazlý, Greenland)

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