Does faster RAM really make a difference?
What sort of modules should I choose?
Unless your computer is a real antique, buying RAM means buying DIMMs: dual in-line memory modules. DIMMs come in several types, and which sort you need depends on your motherboard. If your computer’s more than four years old, it might take plain old DDR DIMMs (known as “double data rate” because memory can be accessed twice per clock signal). More recent PCs will most likely use the faster DDR2 DIMMs, while high-end desktop systems might use the latest DDR3 standard.
The different types of DIMM aren’t cross-compatible: if your motherboard demands DDR2, it won’t work with DDR3. To ensure you don’t make mistakes, different types of DIMM have notches in different places, making it impossible to plug the wrong sort of DIMM into a slot. To find out which type of DIMM you need, look at the modules already installed on your PC: odds are they’ll be labelled either DDR, DDR2 or DDR3. Alternatively, go online and look up your motherboard on the manufacturer’s website, or use a system-analysis tool such as SiSoft Sandra.
A few motherboards based on Intel’s P35 and P45 chipsets provide slots for both DDR2 or DDR3, offering some flexibility. Be warned, though: you can’t use both types at once.
If you have a laptop, you’ll need to use compact modules known as “small outline DIMMs”, or SODIMMs. As with desktop modules, SODIMMs come in DDR and DDR2 flavours, with notches to ensure they’re only plugged into the right sort of slot. DDR3 SODIMMs are starting to appear on the market too, though only the very newest laptops use them.
Is there an optimum number of DIMMs?
We tend to think of a computer’s memory as a contiguous space, but in the physical world it’s normally spread across multiple DIMMs, filling up some or all of the motherboard’s slots. This raises a few practical and technological issues.
One obvious consideration is how many memory slots your motherboard has. Most come with four DIMM slots, though a few have six or even eight, while lightweight systems and laptops often have only two. If you have just two slots free, it makes little sense to fill them with two low-capacity DIMMs, as you’ll be closing off options for future upgrades. Due to the dynamics of supply and demand, it may not make economic sense, either: a pair of 512MB DIMMs can cost more than twice as much as a single 1GB module.
However, two smaller DIMMs can be faster than one large one – as long as your motherboard supports dual-channel architecture. This is a similar system to RAID0 striping, but for memory rather than hard disks: two identical DIMMs run in parallel, acting as one large module with twice the bandwidth of a normal DIMM.
To quantify the benefits of dual-channel architecture, we tried our standard benchmarks with a single 2GB DIMM, then repeated them with two 1GB DIMMs in dual-channel mode. You can see the results in the bottom-left graph on page 102.
We found the benefits varied hugely between apps: dBpoweramp and Photoshop gained no advantage, but Canopus ProCoder completed its tasks 1% more quickly with dual-channel RAM, while 3ds Max gained a 1.5% boost. Our Office tasks ran a whole 5% faster, and the multi-applications test reflected a 3% performance improvement.
If your motherboard supports dual-channel operation, the DIMM slots will be colour-coded in pairs. To take advantage of it, you simply need to install two identical modules in slots of the same colour – which is one reason why DIMMs are often sold in matched “kits”. You may also have to enable dual-channel architecture in your BIOS.
Thoughts on this article? Add a comment below.
Be the first to comment on this article.