Surprised I Didn't Notice This Before...iMac Memory

[rhsgolfer33]

The chipset apple used in the iMac supports dual channel. In the price breakdown intels mobile 945 chipset was used. The mobile 945 has "Support for dual channel DDR2 667 MHz memory technology." So yes having a 2x1GB or 2x512GB would be beneficial. Personally I dont think dual channel is nessecary, your system would still run great with 1x1GB, it would just be slightly faster with 2x512GB and quite faster with 2x1GB.

 

[Mord]

i've said it before and i'll say it again, runnign dual channel is of no benefit unless the memory of single channel memory is less than that of the system bus, it's 667/667MHz thus single channel saturates the fsb.

 

[majorp]

i've said it before and i'll say it again, runnign dual channel is of no benefit unless the memory of single channel memory is less than that of the system bus, it's 667/667MHz thus single channel saturates the fsb.

but now there are two cores doesn't that double the fsb?

so running two 533 dimms in dual channel would give out the same performance as one at 667?

 

[rhsgolfer33]

i've said it before and i'll say it again, runnign dual channel is of no benefit unless the memory of single channel memory is less than that of the system bus, it's 667/667MHz thus single channel saturates the fsb.

I beleive dual channel would still be faster. Crucial says "one controller reads and writes data while the second controller prepares for the next access, hence, eliminating the reset and setup delays that occur before one memory module can begin the read/write process all over again." So even if the FSB matches the memory speed you still have double the bandwith and 2 modules working together to eliminate time between read, write, and startovers. Crucial says to think of it like this "like two relay runners. The first runner runs one leg while the second runner sets up and prepares to receive the baton smoothly and carry on the task at hand without delay."

 

[majorp]

i've said it before and i'll say it again, runnign dual channel is of no benefit unless the memory of single channel memory is less than that of the system bus, it's 667/667MHz thus single channel saturates the fsb.

anybody else have any more info on this? in dual channel mode would it run at 1334mhz? or does running dual channel have no bandwidth increase at all with the core duo?

 

[nutmac]

anybody else have any more info on this? in dual channel mode would it run at 1334mhz? or does running dual channel have no bandwidth increase at all with the core duo?

iMac's FSB is 667 MHz, which translates into 5.4 GB/sec bandwidth. Since iMac Core Duo and MacBook Pro use 667 MHz DDR2 SO-DIMM (5.4 GB/sec in single-channel and 10.7 GB/sec in dual-channel), there should be little or no memory bottleneck. One may wonder then, what (if any) dual-channel memory interface signifies. Here's what.

1. CPU is not the only consumer of memory. Other components such as GPU, hard disk, SuperDrive, USB and FireWire devices, can transfer information directly (without CPU) to and from memory.
2. When memory is running faster than other components, it can be fed to other components at their maximum bandwidth with minimal delay (or latency). With single-channel memory interface, subsequent data is prepared after data is sent to the CPU. With dual-channel, data read from two memory modules are prepared concurrently. As soon as data from the first module is transferred, subsequent data from second module can be fed immediately.

What these mean in real-world performance may not be all that significant. We are talking about 5 to 10% improvement (if at that), which is not very noticeable to most users. But when every little drop matters to you, every little seconds saved could be worthwhile.

 

[duaneusa]

Which one would you choose? OWC or Datamem?

OK Hold Your Horses.

A variety of posts with mis-information.

1) DDR-2 667 MHz RAM is all CAS Latency 5. This is normal. There may be some premium memory out that gets down to CL4 but it will be $$
DDR-2 533 MHz is CL4
DDR-2 400 MHz is CL4 or sometimes 3
Don't make value comparisons against DDR PC3200 CL3 or CL2.5 - these are different animals

Thanks
Trevor
CanadaRAM.com

Hi,

I am planning on getting 2x1GB modules for my soon to arrive iMac Intel Core Duo 17". Based on the discussion in these forums, I have decided to buy from either OWC or Datamem (see links).

http://eshop.macsales.com/item/Other World Computing/5300DDR2S1GB/
http://www.datamem.com/viewcat.asp_Q_C_E_1286

I have e-mailed Datamem they told me that their modules were Infineons, unbuffered and non-parity. OWC confirmed that their modules were CL4, but did not tell me the manufacturer.

So here is my question. I thought that DDR2-667 PC2-5300 modules were all CL5. Everywhere on the web lists memory for the Intel iMac as CL5, so where is OWC getting their CL4 memory from? And, is it really CL4? As I understand it, CL4 is faster than CL5, so I am better to get the OWC RAM...right?

EDIT: OWC HAVE NOW CONFIRMED THAT THEIR RAM IS CL5, NOT CL4 AS THEY WERE ORIGINALLY STATING ON THEIR WEB SITE. THEY HAVE SINCE NOTIFIED THERE WEB SITE TO REFLECT THIS.

Also, OWC states on their site that the modules are "64x8 device based 128x64 Module"; "8 Non-Stacked TRUE PC5300 Devices per side"; and "Low Noise 8-Layer PCB". I have not seen this info listed on other sites. Can anyone tell me what this means? and, is this important?

Is there anything else that I am missing?
Thanks for your help,
Duane

 

[CanadaRAM]

I am planning on getting 2x1GB modules for my soon to arrive iMac Intel Core Duo 17". Based on the discussion in these forums, I have decided to buy from either OWC or Datamem (see links).

http://eshop.macsales.com/item/Other World Computing/5300DDR2S1GB/
http://www.datamem.com/viewcat.asp_Q_C_E_1286
I have e-mailed Datamem they told me that their modules were Infineons, unbuffered and non-parity. OWC confirmed that their modules were CL4, but did not tell me the manufacturer.
So here is my question. I thought that DDR2-667 PC2-5300 modules were all CL5. Everywhere on the web lists memory for the Intel iMac as CL5, so where is OWC getting their CL4 memory from? And, is it really CL4? As I understand it, CL4 is faster than CL5, so I am better to get the OWC?

In general, CL4 RAM is capable of responding faster than CL5 RAM if the motherboard is equipped to adjust to tighter latency timings and take advantage of it. We don't know positively about the Core Duos yet.

It's unusual to see CL4 RAM being offered at a competitive price -- at this point, CL4 RAM is usually a price premium, until the chip manufacturers start turning out faster chips in quantity. Keep in mind that a CL5 667 MHz module will be CL4 if run at the slower 533 Mhz speed. We don't know if a particular module is 'really' CL4 at 667 until we test it in the machine.

Also, OWC states on their site that the modules are "64x8 device based 128x64 Module"; "8 Non-Stacked TRUE PC5300 Devices per side"; and "Low Noise 8-Layer PCB". I have not seen this info listed on other sites. Can anyone tell me what this means? and, is this important?

This is just the detail on how this (and other modules of this type) are put together -most of this is just repeating the standard specs. It's like Ford telling you the grades of steel and the number of layers of undercoat that go into their body panels -- you don't particularly care as long as they are built correctly. All 1 Gb DDR2-667 modules for Macs are going to be 16-chip, 128x64 modules, non-stacked, unbuffered, non-registered, non-parity.

Thanks
Trevor
CanadaRAM.com

 

[duaneusa]

clarification

Keep in mind that a CL5 667 MHz module will be CL4 if run at the slower 533 Mhz speed. We don't know if a particular module is 'really' CL4 at 667 until we test it in the machine.

Thanks for your prompt response Trevor. Could you explain what you mean by the above? Is it saying that it might not really be CL4 at 667 but really CL4 at 533. Consequently, does that mean if it is really CL4 at 533, then it is actually CL5 at 667, and therefore the same CL rating as the DMS ram?

And, given your knowledge of the industry and the ram specified in my earlier post, would you buy the owc ram or the datamem ram?

Cheers,
Duane

 

[~Shard~]

And, given your knowledge of the industry and the ram specified in my earlier post, would you buy the owc ram or the datamem ram?

If I know Trevor, he'll say buy the DMS RAM.