OS X vs XP: 4G RAM

I have just bought 4G RAM from Crucial and installed it in my MBP 15 2.4.
OS X (10.5) sees all 4G - but XP sees only 2.98G! I have checked to see that the RAM is properly installed and all seems OK. What's going on here?

 

32 bit operating systems can only effectively see 3GB of memory. Unless you have XP x64, XP is only 32 bit, so you can only use up to 3GB.

OS X 10.5 (Leopard) is a 64-bit OS, which can effectively use 4GB (and much more) of RAM.

 

Thanks Paul - that explains it!
In any case, it was a worthwhile upgrade!

 

A lot of 32bit systems can see 3.5GB of ram. Some people on the Dell forum on this board have said that their computers recognised up to 3.8GB of ram in 32bit Vista. I know that Dell current notebooks can see up to 3.5GB of ram in 32bit Vista. Some people using other manufacturers computers have reported being able to see 3.2GB or 3GB in Windows. It seems like Apple maybe one of those companies that allows users to see 3GB of ram. Vista 32bit though has the ability to see up to 3.5GB of ram.

 

yer there is a little hack you can do to make your xp 36 bit or somthing and allow up to 4GB of ram I seem to recall reading that somwhere anwyay

 

Part of it also depends on the chipset. The 945PM chipset used in the original Napa Core 2 Duo MacBook Pros like I have only have 32-bit memory address support and the memory addresses of hardware devices are mapped in the 3.2GB-4GB region. So even with a 64-bit OS, you wouldn't get the full 4GB since the hardware devices are there. Some motherboard makers can tinker around with the BIOS and compact things, which some people may be able to get a bit more than 3.2GB. In Apple's case, I believe they did the opposite and instead of just leaving at 3.2GB, they artificially limited it so that only 3GB shows up and declare it the maximum to discourage people from trying to install 4GB of RAM and then complaining about portions missing. I really wish they would undo this though, since I'm planning on getting 2x2GB once the prices come down a bit to take advantage of dual channel support and I'd much rather have 3.2GB than 3GB even if the difference is relatively small.

However, the latest PM965/GM965 chipsets in the Santa Rosa platform support 36-bit memory addressing and Intel has moved the device addresses away so that the full 4GB is accessible assuming a 64-bit OS.

 

Hello Lite - Can you recall where you read about the 4 G hack? I would be interested in trying it if it isn't too demanding. Or do you think Vista might be the answer? (I tried Vista Business but didn't like it and went back to XP SP2)

 

32 bit XP can only see 3gb of ram

 

Vista won't help either unless you get the x64 version.

 

I don't think there is anything that you can do at the OS level to change the max amount of RAM the OS sees. What you can do is enable PAE, which basically changes how the RAM is divided between the kernal and applications. I think it's usually divided 50/50. You can make more available for applications or what the user can access, but it can cause a whole bunch of problems with drivers that assume a 50/50 division and I'm pretty sure applications have to be written to take advantage of PAE too so it's really not worthwhile. It doesn't mean you have more total RAM anyways, just changes how it's divided and who gets to use it.

 

Wrong. This has been discussed before, actually. I had a Dell XPS M1330 and Windows XP 32bit saw exactly 3582MB of my 4GB. Now that I got rid of the M1330 and am using the same memory in my MBP 2.4, Windows XP only sees 2.98GB as the original thread starter states. Very interesting considering both systems use the same Santa Rosa chipset.

 

It's a Windows setting - you need to enable PAE to see up to 4GB RAM, how much you see depends on the hardware, but Win XP's upper limit it 4GB.

My guess is that this was turned on on your Dell and turned off on your MBP, and if you turn it on on the MBP it should see all 4GB because the Santa Rosa chipset allows that.

See here: http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx

On an unrelated note, be careful with that hard drive of yours, I had the same one and it just died 2 weeks ago. 100% data loss, no recovery program would work, even low level DOS based ones like SpinRite didn't work.

 

Fair enough.

On an HD-related note, I'm guessing (hoping) your HD failure was just unlucky, and not common...

 

OK guys - thanks a lot - I'll live with 3G in Windows. Still mucj=h better than 2G!!!

 

Hi guys. So if i get a MBP and have 4GB on it, and have both XP (32-bit) and Mac OS leopard installed, it'll run fine? I know that XP won't see all 4GB of RAM but will it crash or something? I'd be okay with XP only seeing 3GB and having leopard see all 4GB of RAM

 

Your system will be fine soccerjoe05. Come back if you have any problems.

 

thanks stunner.

 

No, nothing happens, it just doesn't see all 4 GB of RAM. It won't crash because of it or anything .

 

Its a combination of both the chipset and the 32bit OS. You will never be able to use 4gigs of RAM on XP 32bit. Some systems see more, some of that depends on how much ram integrated graphics and other things use. That said seeing and being able to actually use are two different things. Flat out 32bit XP wont let you see or use all 4gig.

64bit XP, Vista and Leopard can see and use 4gig of RAM provided they are using a 965/Santa Rosa chipset. The 945 is the limiting factor for a 64bit OS.

Macbooks prior to the 965 officially supported (from apple) only 2gigs of RAM, but people put in 3gig and could see and use it. Some people even installed 4gig to get two matched memory sticks which gave you dual channel performance and sped up the intel 950 graphics card since it uses system memory. The OS could only see 3gig of the 4gig because of the 945 chipset.

The nice thing is that from Santa Rosa/Leopard on its all 64bit with head room to grow. I would not be surprised to see notebooks with 8gigs of RAM in a year or two.