See my sig for system specs... I have 4 sticks of 1gb OCZ pc3200 DDR RAM. When I have 3 sticks in, no problem. When I add that fourth stick, when the comp tries to use more memory, it freezes everytime memory usage hits 3GB.

I know that windows 32-bit only can use up to 4gb of memory, but some of that goes to system resources, PCI devices, etc. and therefore with 4 sticks of RAM, windows only sees about 3gb. Mac OS X sees all 4gb, but freezes if it tries to use more than 3gb.

SO... does anyone successfuly have 4gb working? If so, what are your specs, and did you do anything to make it work or did it just run correctly (to clarify again, the system boots and run, but when it tries to use more than 3gb of memory it then freezes with the gray screen saying I need to restart).

Also... any bios settings that may play into getting this to work correctly?

I read an article not long ago that said some mac's (real ones) have problems with more than 3GB of ram. If you do a google search it shows people with problems above 3GB. Wonder how apple gets it to 16GB on the Mac Pro...

I think that is because it uses the Xeon processor and server architecure; different than what most ppl have (core 2 duos). Looking at the mac store, I don't think they sell the iMac with more than 3gb of RAM. Guess that makes sense. That's ok, I guess i'll just put the extra stick in my other rig...

Unless someone knows a fix or way around this or has it working, of course...

Its only the imacs. macbooks, macbook pros that have the 3 GB problem iirc. Mainly because they use the 945 Mobile chipset and SO DIMMS which i think cannot use 4 GB. The Mac Pro uses FB-DIMMs and a server motherboard so it is not a problem.

Bofors had problems with adressing all 4 GB (i think her got 3.3 or something), make sure you try a 64 bit kernel.

Leopard is going to be a full 64-bit OS, you shouldn't have a problem with 4GB in Leopard. You just have to wait for a couple of months...

when I had a p5w-DH i had 4 gb of kingston ddr 2 667 ram it worked fine but only after i enabled memory remap in the bios would it see beyond 3 gb ........ using the 975 chipset and x1900xtx juz to give u an idea and core 2 duo processor

I just installed 8GB of DDR2 667 on my Intel D975XBX2, a 975-based mobo. So far everything seems to be working fine, the OS reports 8GB.

One thing did seem a bit strange: an app (Matlab) complained it was out of memory when there was no indication all memory was allocated. I am still investigating this...

I have a intel 945gtp and using 4 ddr2 kingston 1gb modules 533mhz and i don't have any problem.
But a part of your ram get lost 3600 megabytes of ram is the max the os can see.

Im glad that i dint shell out for 4 gigs then.

I turned off both HW & SW Memory Remapping in my BIOS settings. This has allowed me to have all four sticks in, which means I am again running in dual channel memory mode (and my memory performance is up again in benchmarks), however only 3gb are available to the OS (sys info shows 4 gigs, activity monitor shows 3 available). Same situation in VISTA. That other 1gb is not being remapped, thats what was throwing off OS X.

So anyway, 4gb installed running in Dual Channel, 3gb available. When Leopard comes out I should be able to use all 4gb.

Strange enough, my mac sees all 4 gigs of G.Skill HZ 800. Works fine when all four sticks are OC'd to 1000 as well.

No issues with RAm here.

My RAM is strange too
Both "About this mac" and "System Profile" Can show normally that I have 4GB RAM, but in the Activity Monitor, It should I have 3.25GB RAM only.
Any body can solve it?

- enable "memory remap" [or "memory remapping feature," or similar] in your motherboard's BIOS.

I'm having the same problem of only getting 3.25GB addressed. I've also posted a thread about this a few weeks ago.
I've read on several sites that this is due to the architecture of 945 mobos which do NOT support memory mapping (at least not in 32bit). 4GB is some sort of sound barrier for ALL components added together on the 945, including all the memory that's already on the graphics, PCI cards, disks etc... Therefore the max amount of addressable RAM is only 4GB minus 'the rest' of the hardware. And it seems like OSX keeps it simple by limiting the RAM to 3.25 on the 945 board.
965, 975 chipsets etc apparently handle this issue in a more advanced way.
Adding 2GB to my existing 2GB made my DVD drive virtually unusable. When I remove the two sticks everything is back to normal. I basically wasted my money on RAM (and I'm afraid the other 945 fellas with more than 3GB as well..)

I solved my DVD issue by removing the two Kingston sticks for good

Once again, to the mega tech heads, correct me if I talk rubbish. I can assure you though that there is no option in my BIOS for memory mapping.

In the G5 that I have at work, I've got 5.5GB of ram.

I'm rendering in C4D and I'm using a total of 3.85gb of ram. the Computer recognizes all 5.5gbs but I'm not sure of a way to see, within ACtivity Monitor, if it's putting all 5.5gb to use or is able to do so.

it's totally a chipset problem. the 945g, and other 32-bit chipsets can only address within the 4gig space. on my 945g, 3.25 is available to both vista 64 and osx86. i haven't had any issues though. many motherboards kinda falsely advertise, imo, a max of 4gigs of ram. any motherboard that lists a max of 4 gigs of will prolly only get around 3.25 in the OS.... any OS. space for memory-mapped IO needs to be set asside for your system componants. in order to get all 4gigs and beyond, the chipset, cpu, OS, everything needs to be 64-bit.

Which means, we need 955X and Up Chipset

Yep.
I hope that DDR2 RAM won't be obsolete when I do my next major upgrade (which is not going to happen till next year...) so I can recycle my unused 120 EUR worth of low-latency RAM...

People have already answered it but the 3GB issue doesn't have anything with OS X to do and all with the chipset to do. That's why the mac pro can use it but the intel 945 based machines can't.

New Macbook Pro will have 4GB RAM SO-DIMM DDRII at most
will 10.4.9 8Q1058 solve this problem?

Basically true as mentioned before, 4GB is the absolute max on the 945 chipset. Indirectly there are differences between OS'es though. OSX shows 3.25GB in activity monitor but Mandriva for instance shows 3.46 (which in my case is closer to reality)...
I'm unable to explain this but it shows that the OS must still be able to have some sort of influence.