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4GB in iMac not detected by Windows

maverick808

maverick808

macrumors 65816
Original poster
Jun 30, 2004
1,145
156
Scotland
I bought a new iMac and put 4GB of RAM in it. OS X sees the entire 4GB correctly, and both System Profiler and Activity Monitor report that the system has 4GB. However, when I boot into Windows XP Professional it reports only 3GB in Task Manager.

To be honest I don't really care if Windows is using only 3GB as I don't often use Windows outside of Fusion, and when I do I certainly don't need anything near 3GB. However, I would be interested to know if anybody knows why Windows does only see 3GB. Is it an inherent limitation of XP or something funny with the new iMac?
 
The ceiling on the 32bit version isn't necessarily 3gb. It can access 4gb of memory, but some of that is for the graphics memory so you'll never see the full 4gb... at least this is my understanding of it.

I have 4gb in mine and xp only sees 2.75gb. I'll eventually buy a 64bit copy of vista, but like you said, there's plenty of ram and I don't need that extra gb.
 
exabytes18 said:
The ceiling on the 32bit version isn't necessarily 3gb. It can access 4gb of memory, but some of that is for the graphics memory so you'll never see the full 4gb... at least this is my understanding of it.

I have 4gb in mine and xp only sees 2.75gb. I'll eventually buy a 64bit copy of vista, but like you said, there's plenty of ram and I don't need that extra gb.
Click to expand...

The next question is how does the 64 bit version run on a Mac? Some of the drivers provided by Mac are 32 bit only right?
 
You may be able to access all 4GB in windows if you disable the default 1GB pagefile.

It was my understanding that 4GB is the most 32 bit windows can address - it does so by splitting it in two banks, one 2GB bank for the kernel and one 2GB bank for applications.

The 4GB total is physical memory + swap - so having the swap prevents XP from using all of the physical memory.

I've never owned a machine with 4GB so this is all hearsay.
 
exabytes18 said:
The ceiling on the 32bit version isn't necessarily 3gb. It can access 4gb of memory, but some of that is for the graphics memory so you'll never see the full 4gb... at least this is my understanding of it.
Click to expand...

This is only true for chipsets that have integrated graphics and shared memory, such as the GMA950 in the Mac Mini and other such PCs using GMA.

For the iMac which has its own video memory, this will not be the case.
 
Windows 32 bit is bust, basically. No hardware reason for it not to see the full 4GB, as long as your hardware supports 4GB (eg Santa Rosa on laptops). The swap pagefile is hard disk space taken up, not RAM, that is why it is call a swap in the first place.

From what I have read, Vista 64 bit is much better than XP 64 bit, but I do not know whether the bootcamp drivers support it at all or useably so.
 
l33r0y said:
This is only true for chipsets that have integrated graphics and shared memory, such as the GMA950 in the Mac Mini and other such PCs using GMA.

For the iMac which has its own video memory, this will not be the case.
Click to expand...

Mmmmmnnn.... No. It has nothing to do with where the memory is located, but rather how much address space is avaliable for memory.

Windows (32bit) is able to address up to 4 GB, but some of that address space is reserved for other uses, such as page files or by some of the devices that you are using, eg. graphics card and PCI cards. A part of the physical address space is therefore unavailable for use by main memory, hence you only see 3 GB.
 
iBookG4user said:
You'll have a terrible time trying to find drivers and there are a lot of problems with the 64bit version. Avoid it.
Click to expand...

I run the 64 bit version of Vista on my XPS1710 with no problems. There aren't any problems with it except for limited driver support with specialized hardware.

Thus drivers for the Mac does concern me...
 
Can Mac Pro show > 2GB too

maverick808 said:
I bought a new iMac and put 4GB of RAM in it. OS X sees the entire 4GB correctly, and both System Profiler and Activity Monitor report that the system has 4GB. However, when I boot into Windows XP Professional it reports only 3GB in Task Manager.

To be honest I don't really care if Windows is using only 3GB as I don't often use Windows outside of Fusion, and when I do I certainly don't need anything near 3GB. However, I would be interested to know if anybody knows why Windows does only see 3GB. Is it an inherent limitation of XP or something funny with the new iMac?
Click to expand...

How did you do it?

I am trying the same with a MacPro with 4 GB of RAM, running MacOS 10.5. Alas, task manager reports only 1.99 GB.

Cheers
 
well what about on the mac side, my system tells me i have 4 GB of ram but menu-meters says i have 3985 MB total, if my GB to MB math is right, 4096 MB should be 4 GB and i actually have 3.89 GB of ram
 
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