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Bootcamp and XP 2GB RAM limit solution?
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Dedicated MacNNer
Join Date: Jun 2004
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Has any solution been uncovered to address the current 2GB RAM limit when running XP 32-bit via Bootcamp? I have 7GB, but can only use 2GB in XP. I've read that this is a common thing, but I can't seem to find any discussion of solutions, short of "upgrading" to Vista. I just can't bring myself to give MS $300 for Vista Ultimate. I get XP free via a campus licensing agreement. Thanks for any help.
Rob
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Mac Elite
Join Date: Mar 2003
Location: Virginia
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No solution 'cept to not use XP. Not sure if SP3 addresses this, prolly not.,.,.,
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Grizzled Veteran
Join Date: Apr 2001
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SP3 can't address a hardware limitation, so it won't fix the problem.
The underlying issue is limits of 32 bit. A 32 bit OS has only 4gb of address space. Addressing space is assigned not only to RAM, but also the memory on the video card, IO interfaces, the firmware (EFI) etc. RAM is actually the last thing given addressable space to ensure all system devices are reachable. Mac Pros have enough devices to chew up 2gb of the 4gb address space, leaving only 2 left over for RAM.
The solution is to run a 64 bit OS. Apple does not provide drivers for XP 64, so Vista 64 is the only supported way to have all of your RAM under Windows on your Mac Pro.
The 64 bit version of Vista Home Basic will allow up to 8GB of RAM to be used, so that would be the cheapest solution. Every retail key of Vista is valid for either the 32 or 64 bit edition, and if you buy a 32 bit disc, you can get the 64 bit disc from Microsoft here. Be careful about buying OEM copies of Vista, as they are specific to what media you get, and Microsoft won't send you a 64 bit disc if you give them an OEM key.
Checking Newegg.com, Vista Home Premium 64 bit OEM is $100. Or a retail Home Basic upgrade (valid with a previous version of windows you own) is also $100. OEM licenses are machine specific, while retail licenses are user specific. Meaning legally, an OEM copy cannot be transferred to a different machine, while a retail copy can.
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<This space under renovation>
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Grizzled Veteran
Join Date: Apr 2001
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Oh, when deciding on what version of Vista to get (if you do), keep in mind that only Business, Enterprise, and Ultimate versions support two physical processors. So if you have an 8 core Mac Pro, or an older 4 core that used two physical chips, you have to run Business, Enterprise or Ultimate. Ultimate OEM copies are still cheeper then $300 though, Newegg shows them to be $170.
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<This space under renovation>
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Posting Junkie
Join Date: Oct 2005
Location: Houston, TX
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Use the /3GB switch with 32-bit XP.
If you want all 7GB, you need a 64-bit OS. 64-bit XP (which is more like Server 2003 + some desktop goodness) is a strange pumpkin; Vista is the way to go for 64-bit Windows.
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Dedicated MacNNer
Join Date: Jun 2004
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Thanks for all the great information, guys!
Mduell, what is the "/3GB switch?" Thanks!
Rob
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Posting Junkie
Join Date: Oct 2005
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It's the option to put in your boot.ini file to get 3GB instead of 2.
JFGI
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Mac Elite
Join Date: Mar 2003
Location: Virginia
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Originally Posted by Drakino 
SP3 can't address a hardware limitation, so it won't fix the problem.
The underlying issue is limits of 32 bit. A 32 bit OS has only 4gb of address space. Addressing space is assigned not only to RAM, but also the memory on the video card, IO interfaces, the firmware (EFI) etc. RAM is actually the last thing given addressable space to ensure all system devices are reachable. Mac Pros have enough devices to chew up 2gb of the 4gb address space, leaving only 2 left over for RAM.
The solution is to run a 64 bit OS. Apple does not provide drivers for XP 64, so Vista 64 is the only supported way to have all of your RAM under Windows on your Mac Pro.
The 64 bit version of Vista Home Basic will allow up to 8GB of RAM to be used, so that would be the cheapest solution. Every retail key of Vista is valid for either the 32 or 64 bit edition, and if you buy a 32 bit disc, you can get the 64 bit disc from Microsoft here. Be careful about buying OEM copies of Vista, as they are specific to what media you get, and Microsoft won't send you a 64 bit disc if you give them an OEM key.
Checking Newegg.com, Vista Home Premium 64 bit OEM is $100. Or a retail Home Basic upgrade (valid with a previous version of windows you own) is also $100. OEM licenses are machine specific, while retail licenses are user specific. Meaning legally, an OEM copy cannot be transferred to a different machine, while a retail copy can.
No way the MacPro's devices "chew up 2GB or memory." XP is only capable of using 2GB of memory and has nothing to do with the number of devices in a MacPro.
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Posting Junkie
Join Date: Oct 2005
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Originally Posted by cgc
No way the MacPro's devices "chew up 2GB or memory." XP is only capable of using 2GB of memory and has nothing to do with the number of devices in a MacPro.
Note he said address space, not memory. But AFAIK it's less than 1GB rather than 2GB.
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Grizzled Veteran
Join Date: Apr 2001
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Early 2008 Mac Pro Quad proc, NVidia 8800, 4GB RAM, Vista SP 32 bit1, Task Manager showed 2048 memory total. I never bothered to load 32 bit Windows on mine, but a coworker had to due to VPN issues with 64 bit. Something in the Mac Pro is eating a lot of address space. Didn't believe it till I saw it the other day. Last time I saw a system consume so much address space was on an 8 physical processor box with 11 hot plug PCI slots. Each slot took around 240MB of addressing space, to ensure that any server PCI device added could take what was needed. That system would boot a 32 bit OS without PAE and only show around 1GB usable physical RAM.
Also, fair warning on the /3GB switch, it's not good to run on consumer systems. Programs have to be compiled with /largeaddressaware to go above 2GB anyhow, and what /3GB does is shrink the kernel space down to 1GB. This can, and does cause problems mostly due to modern consumer video cards coming with high amounts of RAM. If you start getting blue screens after turning on /3GB, turn it back off.
No way the MacPro's devices "chew up 2GB or memory." XP is only capable of using 2GB of memory and has nothing to do with the number of devices in a MacPro.
They don't chew up RAM, but they do take address space. Devices have higher priority then RAM in receiving an address, otherwise the OS wouldn't be able to talk to the devices without an address. Since the devices are at the top, the ram at the bottom without an address can't be used.
XP Pro 32 bit is capable of using 4GB of RAM only due to non technical reasons imposed by Microsoft. 64GB would be usable with PAE, as PAE uses a trick to go to 36 bit memory, dividing the RAM into 4GB (32bit) chunks. Support for PAE has been in the windows kernel since 2000. However, even if PAE was enabled, it too also tends to be a determinate to consumer systems.
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<This space under renovation>
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Moderator  Join Date: Apr 2000
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The /3GB switch changes the virtual memory allocation to 3 gig application/1 gig OS, instead of 2 each. It does not affect the amount of physical memory you can use.
The exact amount of physical memory you can use in XP is not entirely simple. In XP before both service packs, you could - if your BIOS supported it - use 4 GB of RAM and still have space for other devices. This was done through "hoisting", basically moving part of the RAM higher in the addressing space (so RAM might be 0-2 GB and 4-6 GB, and other devices 2-4 GB). This feature had problems with some drivers, and with SP1 (or possibly SP2, don't quite remember) MS decided to stop being so nice and simply limited the address space to 32 bits, and told everyone to go buy XP/64 if they had a problem with that. This limits memory in 32-bit XP to 3 and a bit GB of RAM.
The RAM used by different hardware varies sharply. Video cards take the most, as they must have at least as much space as their video RAM. If the Mac Pro only lets you have 2 gig precisely, then I think Apple's BIOS emulation added that limitation.
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Mac Elite
Join Date: Mar 2003
Location: Virginia
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Originally Posted by P
The /3GB switch changes the virtual memory allocation to 3 gig application/1 gig OS, instead of 2 each. It does not affect the amount of physical memory you can use.
The exact amount of physical memory you can use in XP is not entirely simple. In XP before both service packs, you could - if your BIOS supported it - use 4 GB of RAM and still have space for other devices. This was done through "hoisting", basically moving part of the RAM higher in the addressing space (so RAM might be 0-2 GB and 4-6 GB, and other devices 2-4 GB). This feature had problems with some drivers, and with SP1 (or possibly SP2, don't quite remember) MS decided to stop being so nice and simply limited the address space to 32 bits, and told everyone to go buy XP/64 if they had a problem with that. This limits memory in 32-bit XP to 3 and a bit GB of RAM.
The RAM used by different hardware varies sharply. Video cards take the most, as they must have at least as much space as their video RAM. If the Mac Pro only lets you have 2 gig precisely, then I think Apple's BIOS emulation added that limitation.
Yup, this question was asked and answered years ago when we first got BootCamp...
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