24" iMac and 3GB RAM limit issues

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Level 1

5 points

24" iMac and 3GB RAM limit issues

I have a legitimate concern with the 24" iMac and wanted to know if anyone else thinks it's an issue. Read Apple's tech note on late model 2006 iMacs including the new 24" model.

http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTechRAM/Articles/RAM_implementation.html#//apple_ref/doc/uid/TP40003899-DontLinkElem entID5

In order to use RAM in an interleaved fashion it states you must use matched pairs. Meaning same size and type. SO.....if the new iMacs will take a 2GB SO-DIMM then why won't it register 4GB total? You can configure your new iMac with 3GB of RAM but it won't be interleaved. On top of that 2GB SO-DIMMs are super expensive in the +$700 range. More then MacPro's FB-DIMMs.

I don't see anyone talking about this but it seems to be a legitimate concern.

Dual 2GHz G5, Mac OS X (10.4.7)

Posted on Sep 14, 2006 12:22 PM

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Answer 1

Sep 14, 2006 12:48 PM in response to kdawggie

I really don't see it as an issue at all. The performance benefit of matched pairs of RAM is minimal and three gigs is an awful lot of RAM for the consumer market that the iMac is marketed at.

I would not be surprised if later someone finds out that the 24" will accept 4GB of RAM.

If you really need more than 3GB of RAM, then the Mac Pros are the machines for you. Unfortunately, you can't have it both ways - an inexpensive all-in-one Mac and more than 3GB of RAM.

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Answer 2

myhighway

Level 5

7,270 points

Sep 14, 2006 2:03 PM in response to kdawggie

"if the new iMacs will take a 2GB SO-DIMM then why won't it register 4GB total?"

kdawggie,
Where did you read that it won't register 4GB total RAM?

My understanding is that there is no conflict there. If two of the 2GB modules are installed, they will both show up and, from a hardware standpoint, be registered as 4GB. I presume they would operate as matched pairs, as there would be no reason why they would not. The new iMac Intel's OS limits the use of memory to 3GB, just as the prior iMac Intel's OS limited memory use to 2GB.

I may be mistaken, but unless someone can point out how, I'm sure I can locate the info that I read previously. Seems to me it was probably Apple's "Technology Overview" if it wasn't on this board.

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Answer 3

kdawggie Author

Level 1

5 points

Sep 14, 2006 2:16 PM in response to myhighway

Take a look here:
http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTechRAM/Articles/RAM_implementation.html#//apple_ref/doc/uid/TP40003899-DontLinkElem entID5

And here:
http://docs.info.apple.com/article.html?artnum=304284

It seems that you can indeed put 4GB into your 24" iMac and perhaps it would run interleaved but it won't be able to use it all. So I imagine if you spent $1400 for 4GB of RAM you would want to use it all.

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Answer 4

myhighway

Level 5

7,270 points

Sep 14, 2006 2:37 PM in response to kdawggie

While speculation on future products isn't permitted here, Apple isn't suggesting that anyone install 4GB of RAM, whether Leopard would be able to use it or not.

Based on the current pricing of the 2GB modules, it wouldn't seem a prudent expenditure to use two for consumer uses, much less one, unless one knew there was some financial payback for them. At some point the faster bus speed of the Mac Pro with its bigger and better memory, not to forget the potential 30-inch display, will probably outweigh the overly desireable 24-inch iMac. They designed it this way so that we'd all WANT it!

I WANT one too, but since I'm perfectly happy now, I don't really know why I want it:))

edit-
Oh, yes, I see that second link you provided is what I had previously read. Thanks.

Message was edited by: myhighway

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Answer 5

kdawggie Author

Level 1

5 points

Sep 14, 2006 2:41 PM in response to myhighway

It seems that the limitation may be due to the Core 2 Duo (Merom) architecture. I can't find any computer configuration ,regardless of platform, using a Merom that addresses more than 2GB of RAM.

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Answer 6

Sep 14, 2006 4:57 PM in response to kdawggie

I can't see that as being the case. The merom is a 64 bit cpu and it has the address space to see in the terabytes of memory. Why apple chose to limit it to 3 GBs only they know.

Glor

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Answer 7

Sep 19, 2006 10:49 AM in response to kdawggie

The Core 2 Duo(Merom) is a 64-bit CPU. The Core Duo is a 32-bit CPU. Both of them should be able to handle 4 GB. The only reason I figure that the new iMac only can use 3 GB RAM is probably because of Mac OS is putting some limitations to the address space. When 2 GB was the highest RAM, there was no backside of using the highest address bit for other system purposes, but when Apple decided to allow more RAM, things turned out otherwise. 3 GB is possibly because of backward compatibility with the earlier iMac and/or OS.

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Answer 8

Sep 19, 2006 8:16 PM in response to kdawggie

I'm glad to see I'm not the only one questioning this. I just purchased the 24" iMac, switching from a 1.8 GHz PowerMac G5 with 3.5 Gigs of RAM in it. I was a little concerned about dropping my RAM but figured the processor upgrade would more than compensate. I was correct, but still confused. What is even more confusing is that according to Intel's website the 2.33 GHz Core 2 Duo chip does not exist. This is either a chip designed exlusively for Apple or it is a 2.4 GHz Core 2 Duo reported at 2.33 Ghz. You can configure a Dell with 4 Gigs of RAM in a Core 2 Duo system, but that is their RAM limitation. I would have expected, like the Mac Pro to be able to go as high as 16 Gigs of RAM given the 64 bit processor. Perhaps a firmware upgrade or Leopard will address this issue. For now I am quite pleased with the system at 2 Gigs of RAM.

24" iMac Mac OS X (10.4.7)

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Answer 9

Sep 20, 2006 5:27 AM in response to MacMan1969

Personally, at this point in time, I don't see it as much of an issue. What person buying an iMac for 1299-1999 is willing to pay 1500 for a 4GB ram upgrade? When the prices of ram come down then I might start worrying about it.

Glor

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Answer 10

kdawggie Author

Level 1

5 points

Sep 20, 2006 7:07 AM in response to Glorfindeal

That IS the point, what person paying $2000 for a computer would be willing to pay another $1500 for a 4GB RAM upgrade? I just think right now it's hurting Apple's sales of the 24". The 24" encroaches on the prosumer market and at this point in time an affordable 2GB of RAM may seem adequate now but most likely not in 6 years. Which is how long I had my Digital Audio Power Mac. So I think anyone in the prosumer market NOW, like myself, looking for a machine that will last a few years may look away from the 24" and steer toward the Mac Pros. My needs fall squarely in between the 24" iMac and Mac Pros but unfortunately my budget does not. I could live with the 24" even with the expensive cost of the 2GB SODIMMs. I would in fact wait until the prices fell. What I can't live with is the fact that the iMac will only ever be able to use an uninterleaved 3GB when the possibility of an interleaved 4GB seems to be there. I was only able to keep the Digital Audio because I squeezed every ounce of life I could out of it because of various periodic upgrades.

Reluctantly I'm going with the Mac Pro but I REALLY wanted to get the 24" iMac. Thats all.

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Answer 11

Sep 20, 2006 9:53 AM in response to kdawggie

And that might be exactly the reason apple limited it to 3GB, to push those on the border line to the higher profit margin Mac Pros verses the iMac. By the way, if the 3GB limit is self imposed, it is possilbe for Apple in the future to remove this limit. Personally, I have no intention of keeping my imac 24" from more than a couple of years, so I'm not to worried about the 3GB limit, by then something faster, better, stronger will be out and I'll upgrade again, next time wondering why apple limited the memory to 10 GB 🙂

Glor

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Answer 12

kdawggie Author

Level 1

5 points

Sep 20, 2006 10:10 AM in response to Glorfindeal

How right you are. 🙂

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Answer 13

Sep 20, 2006 1:46 PM in response to Eric Kracinski

I really
don't see it as an issue at all. The performance
benefit of matched pairs of RAM is minimal and three
gigs is an awful lot of RAM for the consumer market
that the iMac is marketed at.

I would not be surprised if later someone finds out
that the 24" will accept 4GB of RAM.

If you really need more than 3GB of RAM, then the Mac
Pros are the machines for you. Unfortunately, you
can't have it both ways - an inexpensive all-in-one
Mac and more than 3GB of RAM.

As has been told earlier in this forum, the new iMac will accept 4 GB of RAM, but can only use 3 GB of them.
By the way: There are more positive things about this 64-bit CPU than just being able to address more than 4 GB. For instance, more registers and ability to handle larger chunks of data. In the future when all Intel CPUs are 64-bit, one can get rid of old and redundant instructions necessary 25 years ago.

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Answer 14

Sep 20, 2006 3:35 PM in response to pink_snow

By "accept" I meant "be able to use and recognize" the 4GB of installed RAM.

As mentioned, it is likely an artifical limit to drive people to the MacPro line.

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Answer 15

Sep 20, 2006 8:42 PM in response to kdawggie

Can anyone tell me why this 1Gb module from Kingston
wouldn't work on my 24" iMac 2.16?
All I kept getting after I installed it was a flashing
LED on the front of the iMac.

Part no.:
KVR667D2S5/1G

Description:
1GB 667MHz DDR2 Non-ECC CL5 SODIMM

Detailed Specifications:
Standard 128M X 64 Non-ECC 667MHz 200-pin Unbuffered
SODIMM (SDRAM-DDR2, 1.8V, CL5)

I believe this meets all of Apple's specs for memory
requirements for this iMac:
200-pin SODIMM, Unbuffered, Non-ECC, PC5300 @ 667MHz,
and even the voltage is 1.8V.

I'm confused.
Thanks for any insights.

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