[chefpastry]

Does anyone know why the new iMacs are limited to 3GB? Is it a problem with OS X? Is it something that can be addressed in the future?

Thanks in advance.

[laxthxdude]

Because Apple is putting a 3GB limit on the machine due to its 'consumer' line up model. That is, if you want/need more than 3GB, they (Apple) wants you to buy the 'Pro' machine in the Mac Pro.

[Rolling Musubi]

Originally Posted by chefpastry

Does anyone know why the new iMacs are limited to 3GB? Is it a problem with OS X? Is it something that can be addressed in the future?

From what I've read, it is because of a limitation in the 945 chipset (at least the 945G/GM, unsure about 945PM) where it can't address all 4GB of memory due to how some of that memory is remapped for things like PCI/PCIe bus addressing (the 945 chipset supposedly does this so that 32-bit Operating Systems can see and use that hardware). Only 3.2GB is addressable by the OS and applications. The Crestline chipset (part of the codename Santa Rosa platform) will probably address this limitation (March 2007).

Maybe someone who keeps up with sort of stuff can fill in the details.

[seanc]

Originally Posted by Rolling Musubi

Maybe someone who keeps up with sort of stuff can fill in the details.

Calling mduell

[P]

I'm sure he can fill in the details, but the short version is that Musubi is right. The chipset in the current iMacs (945PM, 945GM in the low-end) is the one for Yonah (original Core Duo) that also has support for Merom (Core 2 Duo). Apple just popped a Merom in there to stay current. A bigger update would take longer. The 965 chipset family supports more RAM, but that's a desktop chipset intended for Conroe. Don't know if it will support Merom, and in any case it's a bigger retooling.

Short version: Next update will support more, either with 965M (Santa Rosa) or Conroe with 965-chipset.

[imitchellg5]

You could get 4 gigs in there, Apple just won't "support" it, although some Genius' would think that it would be sweet . If someone gives me one to try it on, I'll get the RAM

[Chuckit]

Whether you could fit the RAM in there or not, the OS could not use it, to my understanding.

[kamina]

Someone linked to an Apple document stating something in the following line:

"If you put 4GB of ram in the iMac you will see the correct amount under About this Mac, but applications won't be able to use more then 3GB of it".

[imitchellg5]

I would disagree with that. Apple has said that in the past, but it has not been true. Normally if you look in actvity monitor, you would be able to tell that it is using the "unsupported" RAM. But still, maybe Apple has changed it now.

[kamina]

Yep, I did'nt even read teh document, it was just linked to from some forum.

[mduell]

The chipset docs at Intel say 4GB is supported. Any limitation lower than that (2GB or 3GB) is created by Apple.

Section 1.2.2 on page 19 of http://download.intel.com/design/mob...s/30921902.pdf

[chefpastry]

Originally Posted by mduell

If I recall the Intel chipset docs correctly, 4GB is only supported/validated at 533Mhz, not 667Mhz. Since 945PM (and GM for the mini/MacBook) only supports two RAM slots, I assumed that mean it only supported 1GB per slot. I'm not sure how Apple is making the 3GB configuration work.

I think they have 2GB SO-DIMMs.

[jamil5454]

I guess we won't really know until someone tries. Crucial's pricing doesn't really help, however.

[Eug Wanker]

Originally Posted by jamil5454

I guess we won't really know until someone tries. Crucial's pricing doesn't really help, however.

Crucial costs too much for the 2 GB sticks. They're only $700 elsewhere. BARGOOON!

It will be interesting to see what the iMac tech docs say.

[seanc]

Originally Posted by Eug Wanker

Crucial costs too much for the 2 GB sticks. They're only $700 elsewhere. BARGOOON!

It will be interesting to see what the iMac tech docs say.

Apple charges $750 for 3gb Ram.

[Eug Wanker]

Originally Posted by seanc

Apple charges $750 for 3gb Ram.

We were talking about trying out 4 GB in an iMac. No way to get the extra 2 GB stick from Apple, and 3rd parties cost too much too.

[seanc]

Yes I know I just thought it might be a good price comparison, the 1gb is technically free so it would seem that Apple is charging $700 for 2gb Ram as well.

[mduell]

Originally Posted by chefpastry

I think they have 2GB SO-DIMMs.

Please see the edited version of my post. Intel has updated the chipset specs/docs since the last time I saw them.

But yes, 2GB 667Mhz SO-DIMMs have been out for a while now.

[imitchellg5]

Originally Posted by seanc

Yes I know I just thought it might be a good price comparison, the 1gb is technically free so it would seem that Apple is charging $700 for 2gb Ram as well.

Apple loves overcharging on upgrades of over 1Gb of RAM. And yes, it is like $700 for 1Gb extra. What a rip-off

[Eug]

Originally Posted by imitchellg5

Apple loves overcharging on upgrades of over 1Gb of RAM. And yes, it is like $700 for 1Gb extra. What a rip-off

Apple's 2 GB pricing is quite good. And Apple's pricing for the 3 GB config is also quite reasonable.

[Rolling Musubi]

Originally Posted by mduell

The chipset docs at Intel say 4GB is supported. Any limitation lower than that (2GB or 3GB) is created by Apple.

Section 1.2.2 on page 19 of http://download.intel.com/design/mob...s/30921902.pdf

Yes, the documentation states the 4GB supported amount but there seems to be a chipset limitation when 4GB of memory is installed that doesn't seem to be widely known and has not been pointed out by many motherboard manufacturers. Intel put out a technical advisory about something similar before on a previous server chipset.

Some motherboard makers are now adding a brief note about it since more DIY folks are running into this limitation.

MSI MICRO-STAR INT'L CO.,LTD. 945G Neo2

ASUSTeK has a bit more technical details regarding the limitation in their knowledgebase.

Xensource also makes a very brief note about this in their wiki.

Additionally, some have tried seeing if a 64-bit OS would resolve the issue. Windows XP Pro x64 on a Core 2 Duo E6600 with 4GB memory:



Only after manually (via the BIOS) remapping of the reserved PCIe reserved area on affected chipsets does XP Pro x64 see all 4GB.

Based on some of this information, it doesn't seem to necessarily be an Apple imposed limitation. Hopefully one of the usual hardware review sites can shed light on this when they test the iMac's.

[Simon]

Thanks, Rolling Musubi. Now that's some real information. Just what I was looking for.

[mduell]

Thanks Rolling Musubi!