4GB RAM in an "old" white iMac

ChrisA

macrumors G4
Original poster
Jan 5, 2006
11,604
406
Redondo Beach, California
Yes, I've read up on this. I have the "old" white 24" iMac. I bought the last one they had, after the new aluminum iMac was announced. The maximum RAM supported is listed at 3GB but this requires un-matched RAM sticks and you pay about a 6% to 8% speed penalty for this because the chipset can't do dual channel reads. (But you gain back more performance due to the increased amount of RAM) They say you can put two 2GB parts in but the iMac will only see 3.3GB.

With the price of RAM now lower I may just not care that I'm "wasting" 700MB and install two matched 2GB parts. If I can gain a 6% speedup and also get 0.3GB more RAM it may be worth spending the extra $80 or so.

Question: Has anyone tried this?
 

MK2007

macrumors regular
Aug 31, 2007
121
0
I have the white iMac released in the Fall of 2006. Recently I placed two 2-GB modules into the machine. I bought them as a pair from OWC. There is a maximum of 3 GB available. I have seen no increase in speed whatsoever.

There is no requirement for unmatched pairs. Realistically, the discussion of matched versus unmatched in any machine is a waste of time. Matched pairs made a difference years ago. They don't make a difference anymore. You will not see any difference in speed whether the pairs are matched or unmatched.

The matching is a confirmation that the pair has a close speed relationship with one another. It doesn't imply they were or weren't manufactured together. Nearly every module is within a very tightly regulated tolerance so that practically none of them qualify as unmatched pairs.

Buy a pair for the increase in memory from 2 GB to 3 GB. Don't buy it thinking you will gain an increase in speed.
 

flopticalcube

macrumors G4
Matched pairs really only help when other devices have direct access to RAM, like an integrated video controller. Since the 24" iMac has its own dedicated GPU with its own VRAM, matched pairs running in dual-channel mode will make no difference. MacBooks, minis and 17" iMacs benefit but that's about it.
 

ChrisA

macrumors G4
Original poster
Jan 5, 2006
11,604
406
Redondo Beach, California
I have the white iMac released in the Fall of 2006. Recently I placed two 2-GB modules into the machine. I bought them as a pair from OWC. There is a maximum of 3 GB available. I have seen no increase in speed whatsoever.
So Mac OS X only "sees" 3GB? I'm surprised. I guess I'd have to dual boot into Linux or Windows to see the extra 300MB. But I don't dual boot. I use VMware fusion.

You say "no increase in speed". I'd assume that the extra RAM did something. What did you have installed before adding the two 2GB RAM parts?
 

MK2007

macrumors regular
Aug 31, 2007
121
0
Before I upgraded to the 3 GB (4 GB) I had 2 GB factory installed in my iMac. I must reiterate there was NO increase in speed at all. It doesn't matter, though. I expanded the memory so I could keep several applications open at all times, including Safari, which seems to take the most memory of any application.
 

CanadaRAM

macrumors G5
MR Guide to Intel Mac RAM

The intel Core2Duo machines will support 4 Gb of RAM physically, but only 3.2 or 3.3 Gb (not 3.0 Gb) of that will be accessible to the OS. It is a motherboard hardware addressing issue, and is NOT solved with Linux, Leopard or a firmware upgrade.

Chris: It's expensive for 2 x 2 Gb modules, but you will get that slight bit extra RAM, and you will get a small increase in speed.

(Flopical, the modest improvement is there on all processes in the Mac that involve RAM access... it's just more pronounced on the integrated video machines where the video memory has to queue up for system RAM access as well.)

MK: There was no speed increase because you were going from a dual channel (2x1) config. to a dual channel (2x2) config, so speed of access would be the same. You may have noticed a marginal drop in speed if you had gone to a 1 + 2 config. Where you are gaining in speed is where you have enough programs open that would formerly have exceeded the 2 Gb installed RAM, and been forced to hit the Swap files. Now you can keep more in RAM at once, and the swap file delays are minimized.
 

michaelverdin

macrumors member
Feb 12, 2007
37
0
MR Guide to Intel Mac RAM

The intel Core2Duo machines will support 4 Gb of RAM physically, but only 3.2 or 3.3 Gb (not 3.0 Gb) of that will be accessible to the OS. It is a motherboard hardware addressing issue, and is NOT solved with Linux, Leopard or a firmware upgrade.

Chris: It's expensive for 2 x 2 Gb modules, but you will get that slight bit extra RAM, and you will get a small increase in speed.

(Flopical, the modest improvement is there on all processes in the Mac that involve RAM access... it's just more pronounced on the integrated video machines where the video memory has to queue up for system RAM access as well.)


MK: There was no speed increase because you were going from a dual channel (2x1) config. to a dual channel (2x2) config, so speed of access would be the same. You may have noticed a marginal drop in speed if you had gone to a 1 + 2 config. Where you are gaining in speed is where you have enough programs open that would formerly have exceeded the 2 Gb installed RAM, and been forced to hit the Swap files. Now you can keep more in RAM at once, and the swap file delays are minimized.
You did not answer my question, i'll repeat it ahem;

''Just out of curiosity, does the 'About This Mac' pane show 3.3/4.0GB?''
 

flopticalcube

macrumors G4
Interestingly enough, when Barefeats tested a MacBook Pro (closer to the iMac than a MacBook) with unmatched RAM, they saw no speed slowdown at all.

DO MATCHING PAIRS OF MEMORY HELP?
Though we ran the tests above using matching 1GB SODIMMs in both MacBook Pros (for a total of 2GB), we also ran the same tests in the 15" MacBook Pro Core 2 Duo with one 1GB SODIMM and one 2GB SODIMM for a total of 3GB of memory. We wanted to see if non-matched modules would cause the MacBook to slow down due to the loss of interleaving.

The answer is "no, it didn't slow down." In some cases we saw a gain in speed. An example is Aperture where the "lift and stamp" ran 11% faster with 3GB of RAM. But that's probably due to the fact that Aperture + OS X = more than 2GB of total memory usage.
The one caveat is that since Barefeats provide no margins of error, its hard to say whether their tests are truly meaningful or even indicative.
 

CanadaRAM

macrumors G5
Interestingly enough, when Barefeats tested a MacBook Pro (closer to the iMac than a MacBook) with unmatched RAM, they saw no speed slowdown at all.
The one caveat is that since Barefeats provide no margins of error, its hard to say whether their tests are truly meaningful or even indicative.
No, the real caveat is that they tested a 3 Gb configuration against a 2 Gb configuration. They ran one test while changing 2 variables...

Their test tells us that the gains from the extra 1 Gb RAM (delaying the use of hard disk swap files) often outweigh the losses from losing dual channel. This is application dependant however. If you load up only one or two small programs that could completely live within 2 Gb, you would not see the 3rd Gb helping much if at all. Load up Photoshop or Aperture, which can use 2 or 3 GB all by themselves, and the 3 Gb configuration pulls ahead.

The real test would be 2 Gb single against 2 Gb matched pair.
 

flopticalcube

macrumors G4
No, the real caveat is that they tested a 3 Gb configuration against a 2 Gb configuration. They ran one test while changing 2 variables...

Their test tells us that the gains from the extra 1 Gb RAM (delaying the use of hard disk swap files) often outweigh the losses from losing dual channel. This is application dependant however. If you load up only one or two small programs that could completely live within 2 Gb, you would not see the 3rd Gb helping much if at all. Load up Photoshop or Aperture, which can use 2 or 3 GB all by themselves, and the 3 Gb configuration pulls ahead.

The real test would be 2 Gb single against 2 Gb matched pair.
True. I was generalizing about all their tests when I gave the caveat.
 

MK2007

macrumors regular
Aug 31, 2007
121
0
Just out of curiosity, does the 'About This Mac' pane show 3.3/4.0GB?:apple:
It shows 4 GB, but that does not mean 4 GB is being used.

Application Monitor will show you that only 3 GB is available and the distribution of how it is being used.
 

willie45

macrumors regular
Sep 27, 2007
204
2
Sorry to be a bit slow on the uptake here. I haven't really understood all of the above and would like some clarification.

I am quite new to macs and am awaiting delivery of a late 2006 white iMace 2.16 24 inch this week. It is coming with 1Gb RAM and I want to run it to get the most power I can. Does this mean I should stick in 2 x 2Gb sticks ( quite an expensive option ) or will 1x2Gb and 1x1Gb give me the same result? Alternatively should I just stick 1x2Gb in one slot and leave the 512Mb which is already there, on the other?

The reason I am confused is that according to the Crucial UK website, this iMac doesn't support Dual Channel and the threads above suggest it does.

I will be mostly running Photoshop CS3

Thank you and apologies for my ignorance

Willie
 

wizwaz3

macrumors 6502a
Nov 4, 2006
506
0
Northern Arizona
I remember reading somewhere on here that someone was in an Apple store playing on a 24" white and they found that it was running on 4GB. They asked the workers and they said it was an experiment. So does that mean you can make it work with some tweaks?