Experiments in RAM: Memory Myths Put to the Test

Posted 05/14/2009 at 8:30am | by Gordon Mah Ung

7

Comments

Print

RAM, like water, is a commodity. And just as there’s a clear difference between putrid L.A. County tap water and water choppered in from the peaks of Mt. Everest, the quality of RAM can vary wildly. But quality is not the sole factor to consider when you’re trying to achieve optimum memory performance from your system.

These days, a user is faced with a plethora of options spanning different technologies, speeds, and capacities. We’re here to help you make heads and tails of all that so you’re prepared when you configure your next rig. Armed with a slew of RAM-based benchmarks, we set out to answer three of the hottest questions in memory today: Is DDR3 for AMD’s new AM3 Phenom II CPUs worth the expense? Should you pay for high-speed RAM or stick with the standard stuff? Finally, just how much memory is enough? We test three common amounts of RAM for Intel’s Core i7 to identify the sweet spot.

Intrigued? Then read on.

DDR2 vs. DDR3

AMD’s newest AM3 Phenom II CPUs finally bring DDR3 to the table, but is it worth the price?

If there’s one thing AMD knows, it’s how to be fashionably late to a RAM party. Sure, the company showed up early to the DDR dance and was the belle of the ball way back when, but these days, AMD shows up just in time to stack the chairs on the table.

Just as the company lagged far behind Intel in supporting DDR2, AMD has just now—more than a year and a half after its competitor—launched new AM3 chips that support DDR3, although its marketing of the new RAM standard is anything but enthusiastic. In fact, the company maintains that most consumers will prefer DDR2 because of its lower prices. And in a further display of halfheartedness, the company said that if we somehow got a hold of an AM3 board, we could test it, but the company recommended we use DDR2 and an AM2+ board for official Phenom II testing.

 Look very closely: A Socket AM3 CPU (on left) has two fewer pins than a Socket AM2+ chip.

Not exactly confidence inspiring, eh? To find out what’s behind AMD’s blasé attitude about DDR3, we decided to test a 2.6GHz Phenom II X4 810 with both DDR2 and DDR3.

Before we go on, let us explain just how AMD enabled both DDR2 and DDR3 in the same CPU. Generally, CPUs with integrated memory controllers are locked into the type of RAM they support. With Intel, for example, the company decided to support only DDR3 with its new Core i7 CPU. Intel could afford to make the break because there were no legacy Core i7 DDR2 users. With millions of AM2+ boards out there, AMD couldn’t burn its bridges, so it built the new Phenom II with both a DDR2 and DDR3 memory controller. Plug an AM3 CPU into an AM2+ board, and the DDR2 controller is activated. Plug it into an AM3 board, and it runs in DDR3. Got it?

The theoretical advantage that DDR3 memory has over DDR2 is the former is capable of deeper data prefetching; DDR3 can prefetch eight bits of data per clock cycle vs. four bits for DDR2. So, let’s see how this difference plays out in performance.

AMD builders are faced with the thorny question of whether to upgrade from DDR2 to DDR3.

The Test

For our testing, we plugged the 2.6GHz Phenom II X4 810 into the AM2+ MSI DKA790GX board. We slotted in 4GB of Patriot DDR2 RAM running at DDR2/1066 speeds. We then removed the Phenom II X4 810 and put it into the new Asus M4A79T Deluxe AM3 board. To this, we added 4GB of Centon DDR3/1333 in dual-channel mode. Both were tested with a GeForce 8800 GTX, an Intel X25-M SSD, and Windows Vista Home Premium in 64-bit.

To see just what you get for the trouble of building an AM3 box, we selected a set of synthetic memory benchmark tests in addition to gaming and application tests. We settled on 4GB of RAM for both platforms, since it seems like the sweet spot for dual-channel configurations. We ran the DDR2 at 1066MHz—the highest speed available—and the DDR3 at 1333MHz. If DDR3/1333 doesn’t seem like enough of a spread, we also ran a few spot checks with the DDR3 set at 1,600MHz and found essentially no difference.

The Results

No difference. That’s the story of the day with Phenom II in either DDR2 or DDR3 trim. Well, to be fair, not enough of a difference to write home about. From media encoding to application tests to games, DDR3 seemed to have no impact on performance over DDR2. Even in the synthetic memory benchmarks that push the RAM to its theoretical limits, we didn’t see DDR3 make much of a case for itself. That surprised us somewhat, because you can usually count on increased bandwidth to show an improvement in the bandwidth tests. Even with the RAM ticked up to DDR3/1600 rates, the performance increase was minimal in the synthetics. It’s no surprise that we didn’t see an improvement in the majority of our application tests. PCMark Vantage, which stresses various application workloads, actually saw a slight performance decrease from moving to DDR3, but in the synthetic gaming test, 3DMark Vantage, DDR3 pulled ahead by a slight amount.

With these numbers in front of us, we’re not surprised that AMD wasn’t hot to push us on DDR3 for Phenom III. For AMD fans who have a DDR2-only AM2+ motherboard and are considering chucking it for AM3: Don’t bother. At this point, it’s just not worth it. You’re better off just adding more RAM.

For those looking at a new build of a Phenom II system, the choice is far tougher, but we’d probably lean toward DDR3 and AM3. Sure, DDR2 is cheaper, but DDR3, especially at the lower 1,066MHz and 1,333MHz speeds, isn’t going to break the bank. With AMD’s current AM3 chips, the DDR3 performance isn’t spectacular today, but what if a new spin enhances the performance? We know, it’s wishful thinking, but it’s probably worth the bet. 

Next: DDR3/1066 vs. DDR3/1600