SINCE SKULLTRAIL WAS INTRODUCED it was obvious that an overclocked dual-CPU platform with overclockable dual FSB will also need some overclockable memory to boot - pun intended. We're looking at dual 4+ GHz processors with eight cores total, and FSB supposed to go well above 1600 MHz throughput - two of them at that.
However, due to their AMB buffer chips, FB-DIMMs in their current DDR2 variant are darn hot as they are - even the old 1.8 volt FBD-667 can be hot enough to burn your fingertips when you just touch them at the edge! And that is with a fully open, well fanned enclosure.
Selected FBD-800 modules for the Seaburg chipset used in Skulltrail run both AMB chip and the memory dies run at only 1.5 volts - see the Nanya DIMM in our picture here, for instance. So, their heat and power consumption are OK for the usual DDR2-800 CL5 operation - good enough to come close to AMD machines in memory benchmarks, but not good enough when it comes to overclocking.
What to do then? Two choices: extra strong air flow over the DIMMs, meaning a dedicated fan right on top of the modules. Some mobos, like Asus Z7S WS, have mounting holes around the modules for a fan holder, except that the fan Asus uses isn't exactly fast spinning.
Next step? Heat pipe to cool the AMB. This is what Kingston did, and here is the result today:
These HyperX modules, the first official overclockable FB-DIMM series around, are nearly twice as high as the normal ones, and horizontal airflow is recommended.
I installed them in the fresh Skulltrail system with the updated BIOS 1140 - see our comments on that last week. Keep in mind not to press the DIMMs down on the heat pipe fins during the board insertion, but by the "main body".
I could run dual FSB1700 and DDR2-850 speed at 4-4-3-9 here, without changing the voltage from 1.8 volts! The Sandra 64-bit hit 8.93 GB/s, not bad at all - just a bit more, and we can cross 9 GB/s here. Keep in mind the DIMM is certified for 2 volt operation, it's just that I don't like to think what goes on with its AMB chip at that voltage, heat pipes notwithstanding.
Talking about that, as long as a 2-inch 3,000 rpm fan blew at them, the four heat piped DIMMs felt only barely warm to the touch. I feel these modules need the extra cooling more than many previous non-FBD gamers' modules.
In summary, the first "Enthusiast FB-DIMM" modules look good and perform better than expected, becoming the fastest FB-DIMMs around today - right now, I'm trying to see if 3-3-3-8 FBD-800 may work without burning them, alternatively to push them to CL4 FBD900 on the Asus Z7S WS mobo, as it has a bit better FSB scaling. Watch this space for more on that.
However, what we really need are, say, 4-3-3-9 FBD-800 modules with 2GB capacity per DIMM. Then, we'd have full 8GB with some extra performance boost here. Knowing how much money is spent on an average (soon "average" here will mean freeze-cooled quad-GPU monster) Skulltrail system, 8GB memory is kinda minimum, isn't it? µ
Raw speed, cool operation with heat pipes
Height means more extra work fitting extra fans around
We need 2GB DIMMs with this speed
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