Intel's Core i7 870 & i5 750, Lynnfield: Harder, Better, Faster Stronger
by Anand Lal Shimpi on September 8, 2009 12:00 AM EST- Posted in
- CPUs
Overclocking: Great When Overvolted, Otherwise...
Back when I asked Intel why anyone would opt for LGA-1366 over LGA-1156 one of the responses I got was: overclocking. The most overclockable CPUs will be LGA-1366 chips.
We tried overclocking three different CPUs: the Core i7 870, Core i7 860 and Core i5 750. We overclocked using two different coolers: the retail low profile HSF and a Thermalright MUX-120 (the heatsink Intel is sending around to reviewers for high performance testing). I'll get one thing out of the way: the retail heatsink pretty much sucks for overclocking:
| Intel Core i7 870 | Max Overclock (Turbo Disabled) |
| Intel Retail LGA-1156 Cooler | 3.52GHz (160MHz x 22.0) |
| Thermalright MUX-120 | 4.20GHz (200MHz x 21.0) |
The Thermalright enables higher overclocks by removing heat quickly enough allowing us to increase the voltage to the CPU. While roughly 1.35V is the limit for the retail cooler, The Thermalright MUX-120 let us go up to 1.40V. In both cases you need to have a well ventilated case.
Um, yeah.
Now for the actual overclocking results. We overclocked in two ways: 1) with turbo mode enabled and ensuring stability at all turbo frequencies (both single and multiple cores active), and 2) with turbo mode disabled simply going for highest clock speed.
The results are in the table below:
| CPU | Stock Clock Speed | Max Overclock (Turbo Enabled) | Max Overclock (Turbo Disabled) |
| Intel Core i7 870 | 2.93GHz | Default: 3.39GHz (154 x 22.0) 3C/4C Active: 3.70GHz | 4.20GHz (200 x 21.0) |
| Intel Core i7 860 | 2.80GHz | 3.23GHz (154 x 21.0) 3C/4C Active: 3.54GHz | 3.99GHz (210 x 19.0) |
| Intel Core i5 750 | 2.66GHz | 3.2GHz (160 x 20.0) 3C/4C Active: 3.96GHz | 3.92GHz (206.5 x 19) |
For best performance with all four cores active, disabling turbo mode is the way to go. Otherwise you have to reduce the BCLK in order to make sure your system is still stable when the one-active-core turbo mode kicks in. For example, with our Core i7 870 with turbo disabled we hit 4.2GHz using a 200MHz BCLK. If we used the same BCLK but left turbo enabled, when only one core was active we'd hit 5.4GHz - clearly not realistic with only air cooling.
The benefit of leaving turbo enabled is that you get a more balanced system that's not always using more power than it needs to.
The Core i5 750
Our Core i7 860 sample wasn't that great of an overclocker
Breaking 4.2GHz with our Core i7 870
At roughly 4GHz overclocks for all of these CPUs, it's reasonable to say that they are good overclockers. But how about with no additional voltage and the retail heatsink?
| CPU | Stock Clock Speed | Max Overclock, Turbo Disabled (No Additional Voltage) |
| Intel Core i7 870 | 2.93GHz | 3.37GHz (22 x 153MHz) |
The stock overclocks just plain suck on Lynnfield, you need added voltage to overclock the chip. With more voltage it works just like a Bloomfield or Phenom II, but at stock voltages Lynnfield just doesn't clock very high. And it has nothing to do with yields.
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mschira - Tuesday, September 8, 2009 - link
I wonder if a 4xPCIe RAID adapter directly connected to a PCIe slot that is connected to the CPU is any faster than it is for a Core i7 920....Cheers
Gary Key - Tuesday, September 8, 2009 - link
Less than a one percent difference in my testing so far.Jamahl - Tuesday, September 8, 2009 - link
Why do your benches falsely state 2.66ghz when they are clearly running faster than that?rbbot - Tuesday, September 8, 2009 - link
lol - I've just been berating a reviewer on another site for benchmarking with turbo off! In that case the review wasn't targeted at an overclocking audience, but even here I can't see the argument for benchmarking with it disabled.Yes you do need to turn it off for extreme overclocking, but this review is comparing the chips in their stock configuration and stock configuration is on.
maxxcool - Tuesday, September 8, 2009 - link
As for false, well gee, you were told it was on. Didn't you read that? or are you snakeoils brother?goinginstyle - Tuesday, September 8, 2009 - link
They list the base CPU speeds, it was discussed clearly in the article that turbo is enabled, it is not a false statement for reporting what you will purchase. Apparently you just want to flame bait here and I hope they ban you and the two other nut jobs.rgallant - Wednesday, September 9, 2009 - link
people see what they want to see I guess-I wanted to see the multi gpu test, 1156 vs 1366 , clock vs clock ,fps vs fps ,16x vs 8x on die , not one chip overclocking it's self unless you show the numbers for turbo on and off, what if the 1366 mb used for the benches came out of the box and by the default bios overclocked the i7 920 to 3.8 ,would those numbers be included as stock out of the box. I don't think so , that feature would be turned off on the mb.for the benches. 1156 numbers could mean nothing really.
-all cpu's should been locked at 3.6 at least for the multi gpu test or one test anyways.
-the 8x 8x lane issue is the only crippled feature on the new chips ,and it seems to take a back seat to the $50.00 savings for a mb for a $600.00 i7 870 chip ,or $900.00 CND .lol On sept.05 my local shop had the i7 920 D0 and the i7 860 both at $345 CND.
-good review as always ,just missing that part for me , looking to commit on a 1156 or a 1366 upgrade.
maxxcool - Tuesday, September 8, 2009 - link
Yeah, you got to get rid of snakeoil, he is quiet the troll on the TechReport forums as well. He has been banned from several sites already.andrenb91 - Tuesday, September 8, 2009 - link
i5 is faster than PII's! but gotta wait for the lower end ones come outbecause these $190+ chips aren't the one ones that brings up revenue for companies like amd or intel...of course intel has the upper hand here, it could use as a propaganda do deliver up the slower parts. Amd has value and some good cpus at the lower end... that ones bring profits to the company,amd strategy is looking good for now, but it's design must change (native dual/tripe core versions of Phenom II) and the die size have to get smaller to compete next year (against 32nm low end ones...) well I use amd budget ones, for what I do is good enough, ( thin about $400 pc in USA, live in Brazil...) still, I can play some 40fps games and do some video encoding with my gpu,my point is, amd still have the lower-end market, the problem is, if were some of that people that think pentium is a company name, I would by the pentium cpus instead of amd strange cpus. that's why intel sells a lot more desktops and notebooks, of course the performace is great at some 700+ pcs and laptops, but amd has the lower-end, and there it is what amd is looking for: market share, and taht will pump amd back again by 2011 with its fusion apu, intel already controls 80% of mainstream,and high-end markets, but doesn't have a player for the lower-end, thats what I'm looking for a good old intel cpu that beats p2x3 or athlonIIx4 by intel at about $100. then I'll buy my next cpu, probably an intel, or continue with Amd, time will tell...
andrenb91 - Tuesday, September 8, 2009 - link
sorry for my english and, these benchmarks are for windows only, over linux intel i5 will not have this crazy advantage at all, well but who of us uses linux anyway?(don't lie to me, it's a dual boot...) well my system specs are: phenomII x3 705e,4gb ddr3 1333,hd 4650 basicaly a low-end to mainstream..