Intel's Core 2 Extreme QX6700: The Multi-core Era Begins
by Anand Lal Shimpi on November 2, 2006 2:14 AM EST- Posted in
- CPUs
Overclocking
When Intel's first dual core CPUs hit the market, there was a significant gap in clock speed between them and the fastest single core CPUs. The fastest dual core Pentium Extreme Edition was introduced at 3.2GHz, while you could get a 3.73GHz single core CPU for similar money. The single core Pentium 4 Extreme Edition had a 16.5% clock speed advantage, that you had to give up in order to get a second core at the high end.
Of course back then, clock speed mattered, and it was frequency that got you reasonable performance out of Intel's NetBurst architecture. You gave up much less if you looked at the AMD side of things; their fastest single core CPUs at the time ran at 2.6GHz while the fastest dual core Athlon 64 X2s ran at 2.4GHz.
With Intel's Core microarchitecture, the situation with Kentsfield vs. Conroe is much more like the Athlon 64 vs. Athlon 64 X2. At $999 you've got a dual core 2.93GHz offering or a 2.66GHz quad core offering, and at that price point the decision isn't too hard to make, especially when you take into account that you can overclock Kentsfield pretty well.
Like all other Core 2 Extreme processors, the QX6700 has a mostly unlocked clock multiplier, allowing you to easily overclock to higher frequencies. So while you can't take a Core 2 Extreme X6800 and give it more cores, you can always take a QX6700 and run it at X6800 speeds to have your cake and eat it too.
We managed to get our QX6700 sample up to 3.2GHz (12 x 266MHz) at the CPU's stock voltage of 1.35V, which isn't bad at all considering we didn't employ any exotic cooling. Bumping the core voltage up to 1.3875V we were able to gain an extra 266MHz and run at 3.46GHz.
You lose some overclocking headroom given the added heat output of the extra die on the chip, not to mention that both die have to be capable of running at the overclocked speed, but overall Kentsfield doesn't look too bad as an overclocker's chip. It's not the bang for your buck that the E6300 offers, but at $999 that's not what we're expecting to begin with.
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Staples - Thursday, November 2, 2006 - link
I will eventually be buying an E6600 but I was hoping we'd see a price drop when these quad cores came out. Now they have and we see that the cheapest one is over $800, the price of the E6600 will probably not drop for a while because these processors are not in the same market.rqle - Thursday, November 2, 2006 - link
Price doesnt really interest me as much, the fact that i have a very hard time getting a lot of low end Athlon64 around 2.8ghz, mines seem to max out at around 2.7ghz. Seem like most athlon for some reason like 2.3-2.4 and sometime lower while a whole group at my lan party have no problem push a E6300 past 3.1ghz.Brunnis - Thursday, November 2, 2006 - link
The article seems to state that Kentsfield is more efficient that Conroe. This conclusion comes from power measurements of complete systems. This is a little misleading, since a large chunk of that power is consumed by the rest of the system. Since the CPU only makes up a part of the power consumption, but accounts for a very large performance increase, the efficiency is bound to increase when looking at system power consumption.The Kentsfield CPU itself shouldn't be any more efficient than Conroe. That said, there isn't anything wrong in looking at system power consumption and drawing the conclusion that the computer is more efficient with the quad core. I just don't think that the article was very clear on this, though.
smilingcrow - Thursday, November 2, 2006 - link
The power efficiency figures would look different if a lower power PC had been used as a test bed; the use of dual X1900XT cards distorts the figures to a degree. These CPUs are currently only particularly useful for areas where Crossfire setups are not generally relevant.I used the Anandtech data along with my own C2D data from testing low power systems and came up with the following. The extrapolated figures show the efficiency of each CPU as a percentage of that of the QX6700, which is the most efficient in these two tests:
CPU/Anand PC/My PC
3dsmax7
QX6700 – 100/100
Q6600 – 92.3/92.9
X6800 – 74.7/80.7
E6700 – 69.7/75.7
DivX 6.1
QX6700 – 100/100
Q6600 – 98.4/99.01
X6800 – 92.5/99
E6700 – 87.4/94.4
The PC I used for a comparison uses ~60W less at load than Anandtech’s setup which results in:
130W v 189W for the E6700
172W v 230.5W for the QX6700.
System - Asus P5W DH Deluxe, Nvidia 6200TC, 2 x 1GB DDR2-667, Samsung P120 250GB SATA.
The one thing that was missing for me was the power consumption at idle, as I’d imagine that the dual Dice Kentsfield would take a big hit here. Xbitlabs have figures showing idle power consumption, but they are measured with C1E & EIST disabled which makes them a bit pointless in my eyes. Kentsfield gets a spanking in this comparison although it matches an FX-62.
EnzoM3 - Thursday, November 2, 2006 - link
I can only make assumptions, without any test beds here. Since Quad core is simply two dies of Conroe as this article pointed out, the power consumption of the Quad core should double that of Core Duo. If you use that assumption to compute performance per watt, regardless of what the actual numbers are (as long as Quad uses twice the power of Duo), then Quad actually has lower performance per watt than Duo across the board.Sunrise089 - Thursday, November 2, 2006 - link
If you could isolate the CPU only, you're certainly correct, and PPW will decrease with each additional core due to diminishing returns from scaling. Fortunatly CPUs are part of an entire PC, so when the choice can be painted as quad-core versus two dual-core machines, then the numbers look much better.ATWindsor - Thursday, November 2, 2006 - link
Yeah i agree, the more the rest of the system uses, the more "flawed" the numbers will be, lets say, for arguments sake, that a CPU uses 50 watts, and a twice as fast one uses 200 watts. Tut the rest of the system uses 300 watts, then the total system will use 350 watts in the fist case, and the twice as fast one will use 500 watts, so if you take the whole system numbers, the more power-hungry core will seem like it gives more permformanve per watt, but if you only look at the CPUs them self, the picture is diffrent, the less powerhungry CPU has twice the performance per watt.JarredWalton - Thursday, November 2, 2006 - link
You are right that we could be more clear. You can think in terms of efficiency that we're looking at two dual core systems vs. one quad core if you'd like. If we could isolate just the CPU power draw, we could get real CPU efficiency, but doing so is very difficult.PrinceGaz - Thursday, November 2, 2006 - link
Some sites have indeed isolated the CPU power draw by modifying mobos so that current draw as well as voltage on certain pins can be measured. It is, as you say, very difficult however and each platform you wish to test needs its own modded mobo.One simpler way to at least get a rough idea of actual power comsumption (which could be easily calibrated to provide more accurate figures), and a quite accurate measure of relative power consumption would be to measure the heat given off rather than the electricity going in.
The most obvious way to do that would seem to be with a modified water-cooling setup where instead of the heat being dissipated by an external radiator into air, it is instead transferred into a *large* insulated tank of water with an accurate digital thermometer monitoring the water temperature. This tank of water is not circulated through the water-cooling system, it is there merely for the heat to be dumped into. You then measure the rate at which the temperature rises which provides a good guide to power consumption. You might start at 20C and could probably run the tests up until the water reaches about 40C without any problems, probably 45C would still result in the CPU being kept within safe temperatures.
With a 10-litre tank, you would have 10Kg of water, and each Kg requires about 4.2KJ of energy to heat up by 1C, so it would take about 42KJ to heat up that tank of water by 1C. 42KJ is equivalent to 42KW for 1 second, or more realistically, 42 watts for 1000 seconds (about sixteen and a half minutes). You can probably see where I'm going here: a processor using about forty watts of power would heat up the tank of water by about 4C per hour. Eighty watts would be 8C per hour, and so on. Although not all the energy used by the processor will be dumped in the water due to heat being lost elsewhere, the vast majority of it will be and it will be consistent between different processor models.
If you want an exact figure for power consumption, or rather heat dissipation, then the system could be calibrated by connecting it to a CPU shaped heater element fed with a measured amount of power. Take measurements of the rate of temperature rise at twenty watt intervals up to say two hundred watts (I suspect the line will be fairly linear above about 40W) and you can now say with a good degree of accuracy how much power a given CPU is actually using.
As I say, that's one way you could do it and one which in theory should work very well.
Furen - Thursday, November 2, 2006 - link
Wow, that's a insanely round-about way of measuring power draw. You can also measure voltage and current draw at the CPU voltage VRMs. Regardless, CPU power draw truly doesn't matter with this product since it is two of the older products packed into a single package, no new silicon or anything of the sort. What this means is that theoretical efficiency should be the same but in the real world it'll be slightly worse (due to threading inefficiency). That said, measuring power draw for the whole system does measure the system's ability to make the most out of its power draw.