by Ilya Gavrichenkov
11/13/2010 | 12:00 AM
AMD users may find themselves somewhat disappointed with the recent announcements from the makers of overclocker-friendly memory modules and they have a reason to feel that way. There are DDR3 DIMMs now available with a rated frequency of over 2500 MHz but such high clock rates cannot be enabled on the Socket AM3 platform. As we found out in a recent review, it is quite hard even to start a modern Phenom II X6 up together with DDR3-2000. Thus, the majority of high-speed DDR3 modules offered today are only limited to LGA1156 and LGA1366 platforms and cannot show their best with AMD processors.
AMD claims that a proper combination of a processor, mainboard and memory is required to make DDR3-2000 work on the Socket AM3 platform but in our experiments we couldn’t find that combination even though we used a mainboard capable of supporting DDR3-2000 and a flagship CPU model. None of the overclocker-friendly memory modules rated for 2000 or even 2133 MHz would work as DDR3-2000 on our Socket AM3 testbed then. The highest memory frequency the system remained stable at was about 1900 MHz.
What was the reason of our failure? We thought our CPU was just not a good sample but recently we have found out by consulting with memory makers that the key factor is the memory modules rather than the CPU you use. Most of high-speed DDR3 SDRAM kits are simply not meant for Socket AM3. Instead, you need special memory optimized for this specific platform.
Now we’ve got a new opportunity to test Phenom II X6 processors with DDR3-2000 memory as G.Skill were kind to offer us their Phenom-optimized DDR3-2000 kit marked as F3-16000CL7D-4GBFLS. Thanks to it we've made sure that any Phenom II X6 processors are indeed capable of working with high-speed system memory. You only need an appropriate mainboard out of the numerous models based on the Leo series chipsets (AMD 890FX, 890GX, 880G and 870). The chipset alone doesn’t guarantee such compatibility, though. Right now, there is the following list of Socket AM3 mainboards supporting DDR3-2000:
Now that we’ve established the truth with the DDR3-2000 issue, we want to build a Socket AM3 platform with such memory and benchmark its performance.
Looking through the products offered by the leading makers of overclocker-friendly memory modules, one can come to the conclusion that Socket AM3-optimised DDR3-2000 is quite exotic. This makes the G.Skill F3-16000CL7D-4GBFLS the more interesting as there are but few alternatives available. G.Skill thus enters the elite club of Socket AM3 supporters which includes such famous brands as Corsair, Kingston and GeIL.
The exclusive nature of the F3-16000CL7D-4GBFLS kit doesn’t show up in its exterior or accessories. Moreover, this memory comes in an inconspicuous box made from processed cardboard which is strikingly different from blister packs with gaudy ads that other memory makers parcel their products in. The stickers on the box make it clear that this memory is meant for Phenom II X6 processors and compatible mainboards. The list of mainboards is far from complete and shouldn't mislead you as to the capabilities of the product.
Besides the modules, the box contains a cooler that consists of a frame with two 50mm fans. The frame is secured on the latches of DIMM slots. Unfortunately, these fans are supposed to be connected directly to the computer’s PSU, which means they cannot be controlled or monitored. The fans rotate at a constant speed of 3500 RPM but are quiet and have nice-looking blue highlighting.
By the way, even though the cooler is included into the box, you don't really have to use it. These memory modules prove to be not very hot even without such cooling. This is especially good as you may find it difficult or impossible to install those extra fans on your Socket AM3 mainboard because the CPU cooler will get in the way.
G.Skill engineers must have thought about that possibility and equipped their F3-16000CL7D-4GBFLS modules with massive Flare series heatsinks which should cool them well enough.
Each module is covered with aluminum plates from both sides. The finned top of the plates is shaped and colored in such a way as to resemble tongues of flame. They are fastened with screws and contact with the memory chips via a thermal interface. The modules with heatsinks are 58 millimeters tall and may have problems with CPU coolers that hang above the mainboard’s DIMM slots.
The heatsinks have pretty labels and stickers with the G.Skill F3-16000CL7D-4GBFLS product marking and specs. Here they are:
Although the modules are designed for Socket AM3 systems as their specs suggest, they also have XMP profiles which contain ordinary enough parameters.
Considering that these modules are rather special and can work at a clock rate of 2 GHz on the Socket AM3 platform (something which most high-speed overclocker-friendly memory kits cannot do), we are interested in what chips they are based on. G.Skill must have anticipated our curiosity, so we can only see chips with erased markings beneath the heatsinks.
However, there are some reasons for us to suppose that these chips are from Powerchip Technology. That's not a major manufacturer in the industry, which may be the reason for high-speed Socket AM3-oriented memory to be so scarce. Overclocker-friendly DDR3 modules are mostly based on chips from Elpida and Micron which seem to do not quite well with Phenom II X6 processors.
As for G.Skill F3-16000CL7D-4GBFLS, this memory easily worked at 2000 MHz in our Phenom II X6 system at our first attempt.
However, the modules were not absolutely stable with the timings of 7-9-7-24-1T you can find in their specs. We had to increase the RAS# Precharge parameter to 8 to achieve stability. With the memory timings of 7-9-8-24-1T we had no problems at all.
Now that we’ve got high-speed memory on our Socket AM3 platform, we are going to check out its performance benefits in practical applications.
The use of DDR3-2000 in a Socket AM3 system limits your choice of other components. Particularly, you need an E0-stepping processor, i.e. with six cores, whereas your mainboard should be on the recommended product list.
Besides, you must be aware that DDR3-2000 SDRAM is not listed among the Phenom II X6's standard features. The processor’s memory controller doesn’t have frequency multipliers to clock system memory at 2000 MHz when working in default mode. Therefore you have to overclock your computer to be able to set that memory frequency. With our testbed, we had to raise the base clock frequency from 200 to 250 MHz in order to use our system memory as DDR3-2000. Of course, this affects the rest of the frequencies as well, including the clock rates of the CPU, CPU-integrated North Bridge and HyperTransport bus. So, after changing the base clock rate, you may want to check out and adjust the rest of the frequencies and multipliers.
We will use a Phenom II X6 1090T for today’s tests. Its clock rate increases from its default 3.2 GHz to 4.0 GHz as we raise the base clock rate from 200 to 250 MHz. This overclocking suits us just fine as we know our CPU to be able to work at such settings without any problems. As for the CPU-integrated North Bridge, we additionally increased its frequency with the multiplier to 3.0 GHz. This North Bridge includes a memory controller and L3 cache, so its overclocking helps reveal the potential of high-speed system memory better.
The complete list of hardware and software components used for our test system looks as follows:
We already tested our Phenom II X6 processor with system memory working at different frequencies but we didn’t have modules capable of working at 2000 MHz such as we have now. So, we will take the old results and add the results of the G.Skill F3-16000CL7D-4GBFLS kit to them.
First we run our synthetic benchmarks of bandwidth and latency.
The increased frequency helps raise the practical memory bandwidth and lower its latency. We don’t see anything unexpected here: DDR3-2000 is about 11% faster than DDR3-1666 in terms of read speed and its latency is 9% better.
However, we know that differences in memory subsystem parameters may be smoothed out in real-life applications and complex tests by the CPU's cache. So what will we see?
Indeed, DDR3-2000 doesn't provide big performance benefits in real applications. Its average advantage over DDR2-1667 with the same timings is a mere 1-2%.
The same goes for gaming applications.
Gamers who use AMD platforms may achieve a 1.5% increase in performance if they take the trouble of finding special memory capable of working with Phenom II X6 processors at 2000 MHz. The performance benefits look negligible if you compare platforms with similar memory frequencies but you shouldn’t dismiss the influence of memory on performance altogether. For example, the difference between DDR3-2000 and DDR3-1333 with the same timings is as high as 5%.
By the way, the strong point of the G.Skill F3-16000CL7D-4GBFLS modules is their ability to work with rather aggressive timings. That’s why DDR3-2000 comes out the winner in the tests above. For example, DDR3-1667 SDRAM with 7-7-7-21 timings is just as fast as DDR3-2000 with 9-9-9-27 timings in most cases.
Of course, we are also interested in learning how good the G.Skill F3-16000CL7D-4GBFLS kit is at overclocking. High-speed memory kits often prove to be able to work at frequencies above their rated ones on Intel platforms but we couldn’t check this out with the Socket AM3 platform because our overclocking used to stop before we even reached the rated frequency. But now we’ve got high-speed DDR3 optimized especially for AMD processors.
However, the G.Skill F3-16000CL7D-4GBFLS kit disappoints us in this respect as it can only overclock to 2031 MHz at its default settings (7-9-8-24-1T timings and 1.65V voltage).
We can’t get any further whatever we do. Relaxing the timings, increasing the DIMM voltage, adjusting the frequency and voltage of the CPU-integrated North Bridge are all of no help. Like in our earlier tests, we have encountered an obstacle we can't surpass with the G.Skill F3-16000CL7D-4GBFLS modules.
But when we used the same testbed to overclock memory modules based on Elpida Hyper chips, we faced such a barrier at a much lower frequency. So, the memory from G.Skill, presumably based on Powerchip Technology chips, overclocks better but still shows some internal problems of the Phenom II X6's memory controller which doesn’t work with high-speed memory as successfully as the memory controllers of Intel’s modern processors do.
We also want to check out our G.Skill F3-16000CL7D-4GBFLS memory with a Phenom II X4 processor based on the older C0-stepping core. AMD and memory makers say that quad-core processors from AMD are altogether incompatible with DDR3-2000 SDRAM. Is it really so? We take a newest Phenom II X4 970 and install it on our testbed to find the highest memory frequency for it.
Well, the Phenom II X4 is indeed incompatible with DDR3-2000. The system wouldn’t pass the POST at that memory frequency but the G.Skill F3-16000CL7D-4GBFLS modules proved to be perfectly stable as DDR3-1910. Thus, Socket AM3-optimized memory works well with Phenom II X4 processors but shows best overclocking results with six-core Phenom II X6 products.
The main thing we have discovered in our today's tests is that DDR3-2000 SDRAM is indeed possible on Socket AM3 systems. We now know the prerequisites for that: 1) any Phenom II X6 processor, 2) any of the many mainboards based on AMD’s 800 series chipsets, and 3) specially optimized memory modules.
As you can see, the most difficult requirement is to get such optimized memory. We were lucky to have a dual-channel 4GB kit from G.Skill (F3-16000CL7D-4GBFLS) which proved to be capable of working as DDR3-2000 on our Socket AM3 testbed. This memory kit is not without downsides, of course. For example, the modules are rather large because of the cooling elements, but we don't want to find fault with them as there are almost no alternatives available on the market. If you want high-speed DDR3 for your overclocked Phenom II X6-based computer, we do recommend you this memory kit from G.Skill.
Well, you shouldn’t be disappointed if you don’t find DDR3-2000 modules compatible with the Phenom II X6 as the performance benefits of such memory over DDR3-1600 only amount to 1-2% while memory kits like the G.Skill F3-16000CL7D-4GBFLS are some 50% more expensive. So, we are prone to regard the use of DDR3-2000 modules in an overclocked Socket AM3 system as a luxury rather than a necessity.
Although the optimized modules have no problems working with Phenom II X6 processors as DDR3-2000, there are obvious problems with AMD's memory controller in general. The highest memory frequency this controller permits is much lower than what you can get with Intel processors.
Hopefully, AMD will revise its memory controller so that the company’s upcoming Bulldozer and other architectures will work with high-speed memory without any limitations and reservations, especially as JEDEC-approved speeds of DDR3 SDRAM modules may go as high as 2000 and more megahertz in the very near future.