DDR3-1333 Speed and Latency Shootout

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It's often argued that DDR2 memory is certainly fast enough for today's processors, as Intel's current fastest Front Side Bus (FSB) uses a 1333 MHz data rate. But doesn't this newer FSB require "1333 MHz" memory to perform? The simple answer is no.

Intel has been using Dual Channel mode ever since the days of RDRAM on its earliest Pentium 4's to double memory bus width, simply because back then it was impossible to find memory that was both the same speed and the same bus width as its FSB. The earliest Pentium 4's used a 64-bit FSB with a 400 MHz data rate before DDR-400 became available, but two 64-bit DDR-200 (PC-1600) modules would suffice by doubling the memory bus width to 128 bits...assuming you could actually find a DDR SRAM chipset for the Pentium 4 back then. Dual-Channel technology has stuck around so that today's FSB-1333 is easily fed by two DDR2-667 (PC2-5300) modules in dual-channel mode.

Another argument can be made for running memory "synchronously" to the CPU's FSB: Isn't DDR3-1333 synchronous to FSB-1333? Again the answer is no, as Intel's FSB uses Quad Data Rate technology while the memory is only Double Data Rate. FSB-1333 runs at a 333 MHz clock rate, which is the same clock rate as DDR2-667.

Yet, many users have found small performance benefits from running RAM at up to 1.5x the CPU FSB clock, violating to concept of "synchronous clock speed" superiority. Indeed, this is the likely reason why DDR2-667 became popular long before Intel's FSB-1333 was even considered, and probably why DDR2-800 sells well even to non-overclockers.

While most PC builders won't "need" anything faster than mid-priced DDR2 for a while, DDR3 holds two key benefits over the technology it replaces: First, its maximum chip density has been extended to 8 Gb, allowing a 16-chip module to support a maximum 16 GB capacity. Second, its default voltage has been reduced to 1.50 volts from DDR2's 1.80 volts, resulting in a 30% power consumption decrease per clock speed.

To Buy Or Not To Buy?

One major factor favoring the purchase of DDR3 memory is that Intel is slowly moving all of its chipsets in that direction. The firm first introduced DDR3 support as an option on its P35 Express Northbridge, and the DDR3 market has further been expanded to around half of the newer X38 models. Motherboard manufacturers expect big spenders to be the earliest adopters of new technology, so the majority of ultra-expensive X48 chipset motherboards will likely support only this latest memory standard while it gradually works its way into lower-cost markets.

The latest technology always comes at a significant penalty in value and DDR2 is more than sufficient for most systems, so why the big push? Intel is likely preparing the desktop market for something big, specifically a move of the memory controller from the chipset to the CPU itself. As with AMD's current products, this design eliminates the bandwidth limitations of a FSB and allows future processors to receive data as fast as it can be translated.

It's up to the buyer to decide whether he or she would like to bear the burden of opening up future technology to the masses. Many of us still remember when RDRAM was pushed "needlessly" into Pentium III chipsets such as the i820 and i840 as Intel prepared its i850 Pentium 4 chipset to use the same memory format. The plan was to increase RDRAM availability prior to its necessity, but the market reacted unfavorably. Similarities of today's DDR3 push end there, as Intel isn't forcing it into any market but instead making it a performance option.

That's not to say, however, that DDR3 on Intel's FSB is without merit, as its significantly higher data rate is perfect for FSB overclocking. FSB-1600 (400 MHz FSB clock) is just around the corner, and anyone looking to push a 2.80- GHz FSB-1600 processor (400 MHz FSB clock x7) to 4.20 GHz (600 MHz FSB clock x7) will need memory capable of a 1200 MHz data rate (600 MHz DRAM clock). DDR2-1200 is a rare breed that requires extremely high voltage, top cooling and high hopes that it doesn't quit due to the fact that it's really just overstressed DDR2-800.

So while the majority of Core 2 system builders could compare DDR2-800 prices to those of various DDR3 models, overclockers can view DDR3-1333 as a faster, more economical and reliable alternative to DDR2-1200. Furthermore, as DDR3 edges closer to mainstream availability, overclockers with more restrictive budget should see it eventually reaching their own comfort levels.