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QUESTION: Does Low Latency Memory Make My Quad-Core G5 Power Mac Go Faster?

Originally posted April 21st, 2006, by rob-ART morgan, mad scientist

Up until now, the only advantage we saw to low latency memory on the Quad-Core was with fill rates in Xbench. It didn't translate into real world speed gains. But we saw claims that Photoshop CS2 would gain from the lower latency memory.

We constructed a new action file to test this theory. It generates a 152MB test file with blurred noise. Then it peforms 6 actions (Rotate, Gaussian Blur, Motion Blur, Radial Blur, Lighting Effects, and Lens Flare) without UNDO. Memory Cache Usage was set to 3072MB. Cache Levels were set at 6. Total physical memory was 4GB. Test was done after a fresh restart with nothing else running except Activity Monitor.

During the test we verified that there was no scratch disk activity and that neither real nor virtual memory used by Photoshop exceeded our cache setting.

We tested two different memory configurations.
1. Four PQI Turbo 1GB PC4200 533MHz modules rated at CAS 3 (3-3-3-8).
2. Two OWC 2GB PC4200 533MHz modules rated at CAS 4 (same as Apple's factory memory).

The memory with the higher latency ran the test faster. Hmmm.

When we mixed the memory, installing all 6 modules, the test was completed in the faster 111 second time. Hmmm.

We understand there is a lot of communication between the Quad-Core's memory and the graphics card memory during a game like Doom 3 -- especially when we use Ultra Quality. Maybe the higher fill rates help here.

It was a tie.
Nope. "Faster" memory doesn't seem to help here either.

Some final thoughts
These tests are not the be all end all. We're open to any suggestions you have to test the effect of memory.

But if these tests are valid, you won't gain anything from more expensive, low latency memory. In fact, you may even lose some speed.

Even though the 2GB modules don't seem to be available in lower latency, it makes sense to buy them instead the "faster" 1GB modules. That way you can eventually expand your physical memory all the way up to 16GB.

What are your thoughts?
These tests are not the be all end all. We're open to any suggestions you have to test the effect of lower versus higher memory latencies.

Email , the mad scientist, if you have any comments or suggestions.


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We found really good deals on PC2-4200 memory for the Dual-Core and Quad-Core is at Other World Computing. They are one of the few companies shipping a 4GB (2GBx2) kit and at a radically low price. Check out their PC2-4200 memory page!

For refurbished, reconditioned, open box (as well as new) G5 Power Macs, check with Small Dog and Power Max.


SATA II -- Sonnet Technologies is shipping their Tempo SATA E4P and E4i PCIe PCIe host adapters. They support Port Multiplication enclosures including the one made by Sonnet (Fusion500P).

HighPoint Technologies has a RocketRAID 2320 (8 internal ports) and RocketRAID 2322 (one external infiniband port) -- both compatible with the PCI Express slots in the new Power Macs. Their cards support RAID 0, 1, 0+1, and 5 in the firmware. (These cards currently don't let your Power Mac sleep.)

FIREWIRE 800 -- Aaxeon has a FireWire 800 PCI Express card. We tried it. It works on the Quad-Core, but the write speed are one-half of what we get on the built-in factory FireWire 800 port. There are also sleep issues. (They are working on a FW/USB combo card, too.)

SCSI -- Atto Technology is shipping an Ultra 320 SCSI PCI Express card (UL5D). You can buy it direct from their ATTO store.

Serial Attached SCSI -- Adaptec has a PCI Express version of their Serial Attached SCSI host adapter. I've heard they are planning a Mac verson, but Mac OS X is not listed as one of the supported Operating Systems.

FIBRE CHANNEL -- Apple has posted a link to their PCI Express version of their Fibre Channel card. I expect ATTO's new 4-Gigabit Fibre Channel PCI Express card to be offered in a Mac version.

VIDEO CAPTURE -- Blackmagic Design's PCI Express Capture Card" is now officially compatible with the Dual-Core and Quad-Core G5 Power Macs. AJA has a PCI Express version of their Kona card called the LHe.

AUDIO PRODUCTION -- Digidesign is working on a PCI Express version of Pro Tools HD scheduled to ship before the end of the year.

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2005-2006 Rob Art Morgan
"BARE facts on Macintosh speed FEATS"
Email , the webmaster and mad scientist