DDR3/1066 vs. DDR3/1600

Before you pay for the extra bandwidth, read this

Despite AMD’s statements to the contrary, DDR3 is pretty darn cheap. Yes, DDR2 diehards will scoff, seeing as how you can practically get 4GB of DDR2/800 with a Starbucks coffee, but for those of us who remember paying $500 for 2GB of DDR3 just two years ago, today’s DDR3 pricing is a hell of a bargain.

But that doesn’t mean you should spend indiscriminately. Besides the typical concerns over quality—name-brand memory is always preferable—users face another question: How much bandwidth  is worth the cost?

Paying for higher-bandwidth RAM will get you more performance, but not in every application.

Before we get too far into this topic though, let’s review the basics. Like DDR and DDR2, DDR3 uses double data rate technology, which sends and receives data on both the rise and fall of the RAM’s clock—DDR3 just grabs twice as much data as its predecessor. There are two common designations for DDR3: One is the module name, which describes the theoretical bandwidth, as in a PC8500 module or a PC10600 module. These numbers represent the peak transfer rate in MB/s and can become quite confusing. Quickly, tell us the effective data rate of a PC8500 DDR3 module. We’re still waiting.

Sometimes the module will also helpfully list the effective clock speed—the other common RAM designation—e.g, 1066MHz. But when it doesn’t, you can figure out the effective clock speed of a module by dividing the bandwidth by eight. For example, a PC8500 module divided by eight is 1,066MHz, and PC10600 becomes 1,333MHz. Mind you, this is not the actual clock speed, which is 1/8 the effective clock speed. The actual clock speed of a 1,066MHz module is 133MHz. Why all these inflated bandwidth and clock numbers? It’s a legacy of the old war with Rambus, when the DDR guys didn’t want the original DDR/200 (which ran at a core clock of 100MHz and had a bandwidth of 1600MB/s ) to sound inferior to Rambus’s PC800, which ran at 400MHz and had a bandwidth of 3200MB/s in dual-channel mode. Thus, the single-channel-only DDR/200 module became a PC1600 module. Voilà, it’s a bigger number than PC800! We don’t want to pick old scabs, so the take-away is that we prefer to use the nomenclature of DDR3/1066 or DDR3/1600, which is far less confusing and far more useful.

The Test

For our test, we settled on Intel’s big, bad Core i7. Why? Our previous tests proved it’s pretty much a wash between DDR2 and DDR3 on the Phenom II platform. Furthermore, Intel’s Core i7 features a triple-channel DDR3 controller, and its ballistic speeds seem best suited for our bandwidth test. We used an MSI X58 Eclipse SLI board with a 3.2GHz Core i7, an EVGA
GeForce GTX 280, an Intel X25-M SSD, and Windows Vista Home Premium in 64-bit trim. For RAM, we used 6GB of Corsair Dominator DDR3/1600 modules and 6GB of Qimonda DDR3/1066 RAM. Both were in tri-channel mode. For benchmarks, we selected a variety of synthetic memory, gaming, and application tests.

The Results

Coming into this from the uneventful Phenom II DDR2/DDR3 testing, our expectations were low. That’s not because there’s anything wrong with having extra bandwidth, but we’ve rarely seen it have much of an impact. Our experience has shown us that few applications actually require the added bandwidth that’s available today.

We believed that to be doubly so with Intel’s Core i7 series. The chip has so much excess memory bandwidth that anything more than DDR3/1066 seemed like overkill. With three DDR3/1066 modules in tri-channel mode, the chip has more than 25GB/s in memory bandwidth available. With three DDR3/1600 modules, it has in excess of 38GB/s available. The typical dual-channel DDR2 system today has about 13GB/s of memory bandwidth. While we could imagine the step up to DDR3/1066 having an impact with a Core i7, we were skeptical of the chip needing more than that.

We were wrong. At least partially. We were pleasantly surprised to see the Core i7 kick up some benchmarks by a noticeable amount with the DDR/1600. The extra bandwidth didn’t help everywhere, of course. It made no difference in Adobe Photoshop CS2 or Premiere Pro CS3. Likewise, 3DMark Vantage saw no difference going from 1066 to 1600.
But in PC Mark Vantage in 64-bit mode, we saw a rather healthy 9 percent boost going to DDR3/1600. Quake 4 (which we’ve long used as a bandwidth gauge) also showed a 7 percent improvement. Minor bumps also came in our ProShow Producer and MainConcept Reference encoding tests. The improvements weren’t huge, but they were unexpected, since the tests have historically been purely compute bound. Photodex, the maker of ProShow, has long told us that its hand-written encoder loves faster CPU-to-CPU interconnects, and it apparently gets a small increase in performance from RAM bandwidth too.

More predictably, the synthetic memory benchmarks saw sizable increases from the DDR3/1600. SiSoft Sandra showed a whopping 44 percent increase, while Everest Ultimate showed similar gains of 35 percent to 45 percent.

The upshot of this: Unlike the Phenom II, giving the Core i7 more bandwidth will be worth it for folks who want the absolute tops in performance. Expectations must be tempered, however, because a great majority of applications will likely see very little difference. So if you’re on a budget, saving cash by going with DDR3/1066 or DDR3/1333 isn’t going to kill you. That’s assuming you’re running tri-channel though. Our initial tests with Core i7 showed that there are severe performance penalties for running RAM in single-channel mode. Dual-channel is better, but tri-channel will give you the best performance
possible on a Core i7 system.

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