24 inch iMac - interleaved memory and performance question

Started Sep 12, 2006 | Discussions
b.c. Senior Member • Posts: 1,479
24 inch iMac - interleaved memory and performance question

the new 24" Core 2 Duo iMac has 2 memory slots and supports up to 3GB RAM max, see the developer note here:

http://developer.apple.com/documentation/HardwareDrivers/Conceptual/iMac_0609_SuperDrive/index.html

The spec says max performance is achieved with 2 same size/speed DIMMs in the slots to allow interleaved memory function - i.e. 1GB or 2GB configurations.

My question is this: does anybody know what kind of performance penalty there might be (if any significant) in a 3GB configuration, i.e non-interleaved 1GB+2GB DIMMs?

I guess we may know for sure in the coming weeks as more benchmarks come out, but I'm just wondering if anyone can guess - perhaps based on their knowlege of other Mac systems using memory interleaving, the difference with interleaving active and not.

I'm planning to buy a new 24" iMac to replace an old 17" G4 1GHz/1GB iMac which I currently use for Photoshop CS etc, and I assume with Rosetta the more RAM the better. So perhaps the better question behind this all is: performance-wise, would you think it's better to go for 2GB or 3GB, ignoring cost?
any opinions appreciated.

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modsvsrockers New Member • Posts: 21
Re: 24 inch iMac - interleaved memory and performance question

The performance penalty is close to nil in real-world performance - and completely overshadowed by having an extra GB anyway.

MediumFormat Regular Member • Posts: 121
Re: 24 inch iMac - interleaved memory and performance question

bc, I ordered a 24/2.33 this morning and also questioned the 2/3/4 gig situation.

What about a 2 gig in each slot?

uwe_r Veteran Member • Posts: 3,429
Re: 24 inch iMac - interleaved memory and performance question

MediumFormat wrote:

bc, I ordered a 24/2.33 this morning and also questioned the 2/3/4
gig situation.

What about a 2 gig in each slot?

Due to limitations of the chipset OS X can only address 3 GB on this machine. You would pay for an expensive 2 GB DIMM for nothing, it will only use 1 GB of the second DIMM.

Cheers,
Uwe

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Rod Smith Contributing Member • Posts: 610
Re: Any references?

... or test results you can supply?
--
Rod Smith
Niceville, FL

erik hansen Contributing Member • Posts: 569
Re: Any references?

i don't have any specific links, but as long as dual-channel memory systems have been out, there has always been only a slight improvement in real-world benchmarks with matched pairs. synthetic benchmarks show that memory speed does in fact increase, but it doesn't translate to much in terms of real performance. i'm sure if you do a test on dual-channel memory benchmarks you might find some info.
--
Erik Hansen

Eug Senior Member • Posts: 2,779
Actually, it makes a huge difference...

Actually, it makes a huge difference, but generally only with systems which have integrated graphics. As you're probably aware it's because these machines depend on system RAM for performance. 3D performance on these machines improves dramatically when paired memory is used.

In most tests of machines with dedicated GPU memory though, the vast majority of popular apps show marginal improvements in performance. There are exceptions to that rule however.

erik hansen wrote:

i don't have any specific links, but as long as dual-channel memory
systems have been out, there has always been only a slight
improvement in real-world benchmarks with matched pairs. synthetic
benchmarks show that memory speed does in fact increase, but it
doesn't translate to much in terms of real performance. i'm sure if
you do a test on dual-channel memory benchmarks you might find some
info.
--
Erik Hansen

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