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Veltliner · May 16, 2007, 12:37 PM

I just installed 1 Gigiabyte of PC-2 5300 unbuffered DDR-2 ram.

But in "About this computer" it shows up as PC-2-3200U-288.

PC-2 3200 would not be compatible with my 20" iMac 2.1 Ghz, but the status is "OK".

So, what do I not know about the codes used for naming RAM?

Tomchu · May 16, 2007, 02:28 PM

PC2 = DDR2
3200/4200/5300/etc. = maximum theoretical memory bandwidth (stupid, I know)

PC2-3200 is equivalent to 400 MHz DDR2
PC2-4200 is equivalent to 533 MHz DDR2
PC2-5300 is equivalent to 667 MHz DDR2

What does system profiler say about the speed that your RAM is working at? On your iMac 2.1 GHz (I'm assuming it's a G5?) it should be 533 MHz if you've bought the right kind of RAM.

Big Mac · May 16, 2007, 03:17 PM

Congratulations on getting it installed. As for the speed that's displayed, I don't think it's a big deal. I have read a lot of people are noticing their RAM speed isn't reported correctly. If you're really curious, you could run the Apple Hardware Test disc and see if it reports anything.

mduell · 04:57 PM

It's reporting correctly.
The early G5 iMacs took PC-3200 (DDR-400) RAM and ran it at PC-3200 speeds.
The later revision G5 iMacs took PC2-4200 (DDR2-533) RAM (or better, as you installed) and ran it at PC2-3200 (DDR2-400) speeds.
The same may apply to the PowerMacs, I don't remember.

Switching from DDR to DDR2 at the same clockrate doesn't give any performance increase (it may even yield a performance decrease due to the higher latency), but lowered price (DDR2 is cheaper than DDR) and power consumption (DDR2 runs at a lower voltage than DDR). Why they advertised/sold/shipped PC2-4200 when they were only going to run it at PC2-3200 is also up for speculation: 'bigger number' for sales hype, ease of transition should the memory controller speed up in the future, etc.

Now if only I could remember where on apple.com I read all this.

edit: Brainfart, see below.

Veltliner · May 16, 2007, 08:00 PM

Originally Posted by Tomchu

PC2 = DDR2
3200/4200/5300/etc. = maximum theoretical memory bandwidth (stupid, I know)

PC2-3200 is equivalent to 400 MHz DDR2
PC2-4200 is equivalent to 533 MHz DDR2
PC2-5300 is equivalent to 667 MHz DDR2

What does system profiler say about the speed that your RAM is working at? On your iMac 2.1 GHz (I'm assuming it's a G5?) it should be 533 MHz if you've bought the right kind of RAM.

Yes, I bought the right kind of RAM. It said DDR2 PC2-5300 on the package and on a sticker on the RAM, also on the invoice.

Veltliner · May 16, 2007, 08:02 PM

Originally Posted by Big Mac

I have read a lot of people are noticing their RAM speed isn't reported correctly. If you're really curious, you could run the Apple Hardware Test disc and see if it reports anything.

So at least Crucial doesn't ship RAM that isn't correctly labeled, but it could report wrong. The exact bandwith would be PC2-4200.

Veltliner · May 16, 2007, 08:05 PM

Originally Posted by mduell

It's reporting correctly.
The later revision G5 iMacs took PC2-4200 (DDR2-533) RAM (or better, as you installed) and ran it at PC2-3200 (DDR2-400) speeds.

So you say they do this to save costs, save energy, and have higher numbers for marketing (like the processor speed hype, or the megapixel hype for digital cameras).

Thanks to everybody!

mduell · May 17, 2007, 04:57 PM

I was going crazy trying to find a link to support what I said when I remembered that my comments apply to the DDR2 PowerBooks (which ran DDR2-533 at 333Mhz), not the iMacs, for the same reason (cost and power).

I have no idea why your memory is being reported slower.

Veltliner · May 18, 2007, 06:46 PM

Actually, I asked Crucial.

Crucial really has great customer support.

Crucial wrote:

"If your new PC2-5300 module is recognized correctly by the system but the system profiler reports the new module as "PC2-3200" there appears to be a bug in the System Profiler when PC2-5300 memory is installed (Apple standard memory is PC2-4200)

We can assure you that the PC2-5300 (DDR667) is running at PC2-4200 (DDR533) speed and not the reported PC2-3200 (DDR400) speed."

So it is just a reporting bug, as the 5300RAM has possibly not been available at the time the system profiler has been programmed.

So, it's all roses.

Tomchu · May 19, 2007, 12:25 PM

System Profiler will ask the chipset/memory controller for that information, so ... no. It's not just SP mis-reporting IMO.

The scenario is either that your system can't figure out how to run the PC2-5300 at PC2-4200 (maybe there are no SPD timings stored on the RAM for PC2-4200), and it defaults to a "safe" PC2-3200 ... or as mduell said, those iMacs actually do run at PC2-3200 and the PC2-4200 "requirement" that Apple publishes is simply to make people feel like they're getting a better/faster system.