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Overclocking Intel’s Core i5-750 & i7-870
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by Rob Williams on September 10, 2009 in Intel Processors

We found out earlier this week that Intel’s Lynnfield-based processors are fast, but who said that cranking the clocks to make them even faster was a bad idea? In this article, we take both the Core i5-750 and i7-870 for an overclocking joyride, and the stable overclocks we were able to achieve is nothing short of impressive.

Introduction

For a lot of people, one of the best parts of getting a new CPU to upgrade or to build a new PC is to overclock the heck out of it. It’s a hobby that’s existed for about as long as computers, and why not? As computing enthusiasts, it’s in our blood to always expect more performance from our PC’s components. It doesn’t even have to matter if we need that extra power. It all comes down to knowing that we’re getting as much performance out of our dollar as possible.

But that’s not to say that overclocking doesn’t have a real purpose, either. As long as you achieve what could be considered a 100% stable clock speed, most everything you do is going to get done faster. Depending on the size of the job, you may shave seconds off an encode time, or hours off of a render time. Overclocking isn’t always about creating bragging rights, but making sure whatever you need to get done, gets done as fast as possible.

One other benefit of overclocking is the value proposition, as mentioned above. When the choice comes between two processor models, and one is 10% faster but 50% higher in price, it’s hard to resist picking up the lesser-expensive part and overclocking it. Once again, depending on your situation and what you need to get done on your PC, overclocking essentially boils down to one thing: free performance.

With the launch of their Core 2 series in the summer of 2006, Intel blew the doors open to mainstream overclocking. Prior to that, overclocking was considered tedious, and too sketchy, and it resulted in only tech enthusiasts who paid any attention to it. Core 2, whether Intel planned it to be or not, felt like it was made for overclocking. Even if you didn’t know anything about the process of overclocking, it took no more than a few minutes to figure it out, and 10% clock boosts or higher would be possible with minimal effort.

Since that processor architecture’s launch, Intel has enjoyed an arguable domination where overclocking is concerned. It’s not that AMD’s chips don’t overclock well, because they do, but Intel’s chips weren’t just easier to overclock, but the top-end overclocks were much more impressive. That’s changed a bit since AMD’s Phenom II launch, as we’ve seen evidenced with extreme overclocking.

Overclocking Intel’s Lynnfield Processors

When Intel launched their Nehalem processors last fall (Core i7-920, i7-940 & i7-965 Extreme Edition), the process of overclocking became a little more complicated than what we were used to. Rather than worry about a Front-Side Bus (FSB) and CPU/Northbridge voltages, we all of a sudden had to take things like Uncore, QPI Link speeds and additional voltages – not to mention extra multipliers – into consideration.

But in a way, we’re moving backwards (not a bad thing) with Lynnfield. There isn’t as much to stress over in the BIOS, and whether this is ultimately a good thing or not will depend on how serious of an overclocker you are. Compared to X58 motherboards, we lose a bit of control with regards to voltages primarily on P55, but again, this will matter only to those who plan on achieving extreme overclocks – aka: unstable under regular conditions.

Unlike the Core 2 series before it, Lynnfield has another factor at play: Turbo. Simply put, Turbo is a technology that allows a processor to boost its performance beyond its rated speed. In the case here, if a processor has a multiplier of say, 20x (meaning, Host Clock (133MHz) * 20x), Turbo might push one core with a 22x multiplier, meaning that when active, the frequency would be Host Clock * 22x.

For a more robust explanation of what Turbo is and exactly how it works, please refer to a page we dedicated to the feature in our recent launch article. Turbo, though it may not seem it at first, is very important to achieving higher overclocks. Because we’re able to go a multiplier beyond the CPU’s maximum, it means we likewise reach a higher frequency. So, for more than one reason, we can thank Intel for this feature.

Another nice aspect of Lynnfield overclocking, is that unlike the X58 launch last fall, there are many motherboards that fall well under the $200 price point. The board we used for all of our testing is actually a bit above $200, at ~$220, but we’re confident that the overclocks we’re about to show you will be achievable on almost any launch motherboard. You might not get away with as low voltage values as we did, but it sure wouldn’t take much to match or surpass what we’ve achieved.

Here’s a shot of the motherboard we used for all of our testing and overclocking, Gigabyte’s P55-UD5:

Judging by what I’ve experienced over the course of the past few weeks, I’d heartily recommend this board to anyone looking for a feature-robust and affordable offering. It wasn’t only a pleasure to use, but made overclocking a straight-forward affair, and that’s a major plus. If the price tag is a little bit higher than what you’d like to pay, Gigabyte offers many variants of their P55 series at different price-points – one as low as $140.

So how about we move right into our overclocks then, huh? Well, first, please take a moment to review our test PC specs, and also our blurb below which explains what we consider to be a stable and worthwhile overclock.

Component
Intel LGA1156 Test System
Processors Intel Core i7-870 – Quad-Core, 2.93GHz, ~1.25v
Intel Core i5-750 – Quad-Core, 2.66GHz, ~1.25v
Motherboard
Gigabyte P55-UD5 – P55-based, F3 BIOS (08/01/09)
Memory

Corsair XMS3 DHX 2x2GB – DDR3-1333 7-7-7-20-2T, 1.65v
Graphics
ATI Radeon HD 4870 512MB (Catalyst 8.11)
Audio
On-Board Audio
Storage
Power Supply
Chassis
Display
Cooling
Thermalright MUX-120
Et cetera

As I’ve mentioned in past content, I’m not as interested in finding the highest overclock possible as much as I am interested in finding the highest stable overclock. To me, if an overclock crashes the computer after a few minutes of running a stress-test, it has little value except for competition.

How we declare an overclock stable is simple… we stress it as hard as possible for a certain period of time, both with CPU-related tests and also GPU-related, to conclude on what we’ll be confident is 100% stability throughout all possible computing scenarios.

For the sake of CPU stress-testing, we use LinX. Compared to other popular CPU stress-testers, LinX’s tests are far more gruelling, and proof of that is seen by the fact that it manages to heat the CPU up to 20°C hotter than competing applications, like SP2004. Generally, if the CPU survives the first half-hour of this stress, there’s a good chance that it’s mostly stable, but I strive for a 12 hour stress as long as time permits.

If the CPU stress passes without error, then GPU stress-testing begins, in order to assure a system-wide stable overclock. To test for this, 3DMark Vantage’s Extreme test is used, with the increased resolution of 2560×1600, looped nine times. If this passes, some time is dedicated to real-world game testing, to make sure that gaming is just as stable as it would be if the CPU were at stock. If both these CPU and GPU tests pass without issue, we can confidently declare a stable overclock.


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