|DDR3 RAM: System Memory Technology Explained|
|Articles - Featured Guides|
|Written by Olin Coles|
|Saturday, 10 May 2008|
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DDR3: Overclocker Functionality
So let's pause for a moment to recap what we've covered: DDR3 RAM modules can conserve up to 32% of the energy used on system memory, while at the same time saving money on maintenance costs for enterprise HVAC systems. The data prefetch buffer has doubled from only 4 bits per cycle to a full 8 bits with each pass. Finally, the Fly-by topology removes the mechanical limitations of physical line balancing by replacing it with an automatically controlled and calibrated signal time delay. Not just a speed improvement, like some would like you to think.
So then, when was the last time enthusiasts were actually encouraged to overclock their system memory by the manufacturer? Better yet, when was the last time Intel endorsed the practice? To be fair, Intel processors have been capable of overclocks for quite some time already, but not nearly to the level of convenience introduced in XMP technology.
XMP, or eXtreme Memory Profile is an automatic memory settings technology developed by Intel and Corsair to compete with Nvidia's SLI Memory and Enhanced Performance Profiles (EPP). It works very similar to EPP, with one major exception: XMP manages everything from the CPU multiplier, to voltage and front side bus frequencies. This makes overclocking one of the easiest thing possible, since it only requires an XMP compatible motherboard such as Intel's X48 series and an XMP enhanced set of system memory modules.
The XMP Specification was first officially introduced by Intel on March 23rd, 2007 to enable a enthusiast performance extension to the traditional JEDEC SPD specifications. It is very common for Intel Extreme Memory Profiles to offer two different performance profiles. Profile 1 is used for the hardware enthusiast or for certified settings and is the profile that is tested under the Intel Extreme Memory Certification program. Profile 2 is designed to host the Extreme or Fastest possible settings that have no guard band and may or may not work on every system. It should also be noted that XMP settings are not always defined as overclocked or over-volted components. In some less common cases, Extreme Memory Profiles can be used to define conservative power saving settings or reduced (faster) latencies timings.
CAS Latency Timing
CAS latency timing is not something new to DDR3, and it is one of the few items that remains unchanged in the new format. You may wonder why I used the term "unchanged", when every enthusiast in every web forum world-wide has jumped on their soapbox and chastised anyone considering DDR3 because of the higher latencies. The simple fact is that you cannot extend base frequencies without also extending the CAS delay, and DDR3 is actually requires less latency in comparison.
As a quick refresher, you might recall that 1066MHz DDR2 began with CL5 and CL6 latencies, and eventually improved to CL4 in rare cases of special IC module binning. So it should be considered a vast improvement in comparison that 1333 MHz DDR3 can achieve CL5, and some 1800 MHz DDR3 modules such as Corsair's PC3-14400 kit which have received careful parts binning can operate on CL7 timings.
Putting this arguement into greater perspective, drift back to the first days of DDR2. I can still remember the complaints back then, although to a lesser extent, about the increased latency. Back in those days, 400 MHz DDR was often times seen with CL2 timings, so keep that in mind when you look at the 800 MHz DDR2 presently available at a 100% latency increase to CL4 timings. In comparison, the CL7 timings of 1600 MHz DDR3 are still ahead of the curve by 25%, or even up to 50% faster latencies with OCZ's CL6 DDR3.
The bottom line is that enthusiasts need to hone in on the truth behind the technology, and ignore the self-serving ignorance that often runs rampant in most technology forums. The same person who condescends the idea of using DDR3 is also the same person who doesn't know the reason for the difference in architecture. The reality of the matter is that DDR3 is actually a better memory in terms of latency timings, especially compared against DDR2. So now imagine how tight the timings will be once the now infantile manufacturing process evolves from 90 nm to 70 nm; these latency timings will only get better.