As your geek friend has probably told you, desktop computer memory is in a transitory phase, moving from DDR2 RAM to DDR3 RAM. No one expects DDR3 to really take hold until next year, when quad-core processors sprout up like veritable weeds on the PC landscape.

For the time being a strange situation exists where motherboard makers are releasing identical Intel P35 Express boards, save the memory standard they adopt; either DDR2 or DDR3. By mid to late 2008 however, the DDR3 memory standard should account for at least half the Intel motherboard market, if not more. It's hard to say where AMD will fall in with all of this, its 'K10' microprocessor architecture is not expected to adopt DDR3 RAM until 2009.

Differences in memory: DDR2 and DDR3 are not interpretable

As with all new standards, it's important to state the obvious right from the start to minimize confusion. Computer RAM has been around for many years now, and in our time PCSTATS has seen it transition from SDRAM to DDR, and from DDR to DDR-2 memory. It’s important to note that while DDR2 and DDR3 Dual Inline Memory Modules (DIMMs) are physically the same size, and contain the same number of little gold connector pins (240), the modules are keyed at different spots and are not interchangeable.

DDR3 RAM will not work in a DDR2 motherboard even if the chipset is technically DDR3 compatible (ie. Intel P35 Express). Conversely, a DDR3 motherboard is not backwards compatible with DDR2 memory modules... despite your best intention to reuse those once very expensive puppies.

These are 1.5V DDR3 memory slots (above), and below you can see a DDR3 memory module over top of a DDR2 module. Note the subtle difference where the DDR3 module is 'keyed' with respect to the DDR2 module. Both memory standards have exactly 240 gold connectors, but DDR3 operates at 1.5V, DDR2 at 1.8V.

New memory standards are almost always made incompatible with old ones for a couple of very important reasons... Voltage and data transfer architectures are usually to blame. Surprisingly, prying more money out of your wallet by forcing you to buy completely new hardware doesn't technically factor in.

Placed edge to edge, it is easy to see the physical difference between DDR2 and DDR3 modules rests with where that small key space is positioned. It prevents DDR2 memory from being installed in a DDR3 motherboard and vice versa. The pins as may notice, line up perfectly.

The main difference between DDR-3 memory and its predecessor is that DDR3 operates with less voltage. DDR-3 RAM runs with 1.5V, while DDR2 demands a little more, 1.8V. Next, unique memory slots prevent you from running DDR3 memory in a DDR2 memory slot and vice versa. The memory standards themselves are not inter-compatible, so neither are the sockets.

But system memory is system memory right? Yes, but not quite. Think of it like coffee and tea. Each beverage requires a specialized preparation and brewing method, but the end result in both situations is a hot caffeinated liquid. If you try to brew coffee in a tea pot, or tea leaves in an espresso machine... well, neither works.

On top of the key differences, JEDEC standards dictate desktop DDR2 memory speeds to between 400-800 MHz, although chipset and memory manufacturers have pushed DDR2 speeds much further.

Intel’s P35 Express chipset for example, will run DDR2 memory as high as 1066 MHz.

The JEDEC standards for DDR3 memory on the other hand start at 800 MHz and currently run as high as 1600 MHz. While there is a bit of overlap in terms of speeds, that is not likely to last. At the moment most DDR3 memory comes in two flavors, 1066 and 1333 MHz, but the speeds will increase as the memory standard matures.

DDR3 vs DDR2 Memory Performance?

The quick and simple explanation is that at the same speeds, DDR2 and DDR3 desktop memory will perform roughly the same. In the long term DDR3 memory should take the lead. Manufacturers will eventually increase bus speeds and memory operating frequencies to meet the memory bandwidth demands of the next generation quad and multi-core processors, and demanding computer users of course. ;-)

Next up, PCSTATS speaks about the Intel P35 Express chipset. Is it Intel's best and brightest, or just a mainstream stop-gap until the Intel X38 Express arrives?