Dual Channel Memory Primer

If you go browsing around the various online hardware resellers, or are looking at the websites of many motherboard and memory OEMs, you'll see quite a bit of buzz about "Dual Channel" memory. All the modern chipsets and motherboards on the market today support "dual-channel memory". This may leave you wondering - what exactly is Dual-Channel memory and should I upgrade to a platform that supports it? With all of the buzz about it, the answer may surprise you.

<small>A Pair of Matched DDR Modules</small>

Behind The Technology

Dual Channel memory is actually a relatively simple technology. Dual Channel memory is method where two memory modules are given their full theoretical bandwidth. Now, at first glance this may seem like it is going to double the bandwidth of your memory. In practice, however, this is not true. What it does allow is for greater efficiency, and through that efficiency greater performance.

When RAM is configured in a Dual-Channel configuration, two similar modules are placed in two different banks, rather than the traditional DIMM configuration of buying the largest single module you can fit in a slot. So, instead of buying a 512MB DIMM, you would buy two 256MB DIMMs. Each DIMM must be in the matching slot for a Dual-Channel Configuration to function properly. These will usually be labeled "Bank 0" or "Channel A" and "Bank 1" or "Channel B". Within these channels are two DIMM slots, DIMM 0 and DIMM 1. If you wanted to configure a dual-channel configuration you would insert modules that match in size, speed and configuration in the matching slots in each bank. For instance, if you had the two 256MB modules I mentioned before, one would go in Channel A DIMM0, the other would go in Channel B DIMM0. This is the physical configuration that will allow for Dual Channel operation.

The greater efficiency I mentioned above is provided by the fact that each of these modules now has access to the full theoretical bandwidth possible, since each channel is independent. This allows one module to function independent of the other, so one module might be performing a write operation while the other is preparing a read, as opposed to having to do the operations in sequence and have one module wait for the other to complete its operation.

Performance

The system used for the following benchmarks is an attempt to gather an "average" mid-range system, and was configured as follows:
CPU: Intel Pentium 4 2.4GHz with HyperThreading
Motherboard: Intel D875PBZLK
RAM: 2x256MB PC3200 Memory Modules by Crucial Technology (Model 8VDDT3264AG-40BC4)
OS: Windows XP Service Pack 1
Video: ATI Radeon 9600 Pro clocked at 465MHz CPU/330MHz RAM
Audio: Sound Blaster Audigy 2 ZS
Hard Drive: Maxtor SATA 6Y080M0 80 GB 7200RPM Hard Drive with 8MB Buffer
DVD-ROM: Plextor PX-116A

AIDA32 Memory Benchmark

AIDA32 is a free system information utility that allows you to explore many aspects of a Windows system. Among the many tests and statistics it provides is a memory test which benchmarks the read/write bandwidth of system memory. These results are a theoretical maximum, and in practice such differences in performance could only be seen in the most memory intensive applications.

Here we see a huge difference in theoretical bandwidth. Unfortunately, such increases do not necessarily reflect actual real world performance increases.

AquaMark3

AquaMark3 is a synthetic benchmark designed to determine the performance of future games by utilizing advanced features not presently seen in most mainstream games.

While you might not know it from the scale, we see very little performance increase in AquaMark3, with a spread of only 442 points, or about 1.5%.

3Dmark 2001 "Special Edition"

3Dmark 2001SE is a very popular benchmark from FutureMark, formerly known as "MadOnion.com". 3Dmark 2001SE is a synthetic test based on engines similar to those in popular DirectX 8.1 titles from the time of its release.

Here again we see a difference of only 181 points, or 1.5%.

3Dmark 2003

3Dmark 2003 is similar to 3Dmark 2001SE, except it is based around DirectX 9 and uses features similar to current games.

Here we see even less of a difference than the previous synthetic benchmarks - only 20 points, or 0.5%.

Final Fantasy XI - Benchmark 2 - High Resolution

Square Enix had already enjoyed a large following in Japan when they released their multi-continent cross-platform Final Fantasy XI MMORPG into the North American market. Before its North American release, they released a benchmark based on the FFXI engine to demonstrate performance of the game on the PC. The game uses Direct X 8.1-based rendering technology.

Here we see the single channel system with a score 106 points behind that of a dual channel system, which is roughly a 2.5% difference.

Halo

Microsoft's banner XBOX Title has become a hit on the PC, and it includes an easy method for benchmarking performance by testing how quickly its in-game cutscenes are rendered. Halo is a DirectX9 Title that is very demanding on even the best hardware and uses advanced features.

Here we see that Halo is less limited by memory performance than it is by video and CPU performance. Due to this, there is little difference between Dual and Single Channel Performance.

Unreal Tournament 2003 Demo 'Flyby' Benchmark

Atari/Epic's popular online shooter uses DirectX 8.1 rendering technology. The 'flyby' demo demonstrates the speed with which the engine can render the game environment.

Here we see a difference of at most 3 frames per second in ideal conditions, with the difference becoming non-existent at higher resolutions. At 1600x1200 the memory configuration mattered so little that the final results ended up with the single channel system coming out on top.

Conclusions

When new technology comes out, there are those who adopt it early, and there are those who must choose their upgrades more carefully. Dual channel memory configurations are more of an evolution than a revolution - it was simply the next logical step. When purchasing a system, you will obviously want to purchase one with Dual Channel capability, because it adds little cost to the system and does provide an overall performance boost. For those upgrading, it may be a more difficult decision. If you are purchasing a new motherboard and using older RAM, you may have a single DIMM configuration that is incompatible with a dual channel configuration. If this is the case, it makes more financial sense to stick with a single channel configuration.

Last, I want to comment on some of the advertising practices being used in the memory industry. Many manufacturers are labeling their memory as "Dual Channel RAM", which while not being deceptive is not entirely accurate. Any DIMM made since PC2100 became a standard could be "Dual Channel Memory" when used with the right motherboard. When purchasing memory, always look beyond the buzzwords and make sure you are purchasing memory from a reliable company with good support and a good reputation. Bad memory can be the nail in the coffin of an otherwise stable system. The Crucial Technology memory used in this test ran without missing a beat throughout all of these tests, in both configurations.