Intel Core i7-875K And Core i5-655K Battle Beyond 4 GHz

Do you like the idea of an unlocked clock multiplier, but don't want to pay $1,000 for an Extreme Edition? Intel's K-series CPUs bring overclocking down to the mainstream. The question is: can these scalable parts keep up with AMD's Black Edition CPUs?

Editor's note: We're partnering up with CyberPower to give away a PC valued at $1,499 based on Intel's Core i7-875K processor. The contest details are on the last page of this review. Make sure you enter to win!

Seven years ago, Intel was a rigid company. It vehemently discouraged overclocking—after all, that was just another way for unscrupulous resellers to liquidate lower-end processors as higher-margin parts.

But then it let loose the Gallatin-based Pentium 4 Extreme Edition running at 3.4 GHz (not a far cry from where the 3.33 GHz Core i7-980X Extreme Edition sits today, in fact). Among the chip’s differentiating features was a 2MB L3 cache that added a bit of performance.

Over time, Intel did more to set the $1,000 Extreme Editions apart from the rest of its desktop lineup. Most notably, it granted the EEs unlocked clock multipliers, simplifying overclocking without officially sanctioning the practice. The problem: only someone willing to drop a grand got access to that nifty little feature. And really, how many of us have a spare thousand bucks lying around?

Meanwhile, in an effort to excite enthusiasts (despite an overall performance disadvantage), AMD has, over the years, launched a number of Black Edition processors also armed with unlocked clock multipliers. Of course, the main difference between Intel's and AMD's efforts is that AMD’s unlocked parts are significantly cheaper. A Phenom II X2 550 Black Edition sells for less than $100. Even the company’s flagship Phenom II X6 1090T Black Edition sells for $310—less than a third of Intel’s Extreme Edition parts.

Don’t get it twisted, though. AMD’s offerings cost less because they aren’t as fast at their stock speeds. You could even say that they’re priced competitively. It just so happens that overclockers don't really care about stock, default, or vanilla ice cream, though. They want to know what happens when you crank the dial, fire the afterburners, and add caramel sauce to the sundae that is a performance PC.

Intel Gets With The Program

Because it’s seen as the company more sympathetic to the power user’s quest for control over his machine, many enthusiasts buy AMD-based hardware on principle. That's not the way I shop, but I read enough of the comments section to know what some of our most vocal readers think.

Sure, Intel has loosened up over the years with high-end desktop SKUs, more flexible motherboards, and even the dual-socket Skulltrail platform. But the fact that its flashiest fare is also prohibitively expensive almost feels like a slap in the face to the very tenets of overclocking: garnering maximum value by optimizing affordable hardware, Celeron 300A-style.

In an almost-unbelievable move, however, the company is giving enthusiasts something that AMD formerly had the monopoly on: reasonably-priced, unlocked parts that have the potential to overclock like hell.

Meet the Core i7-875K and Core i5-655K. Aside from their K-designators and unlocked core/memory multipliers, both SKUs are exactly the same as processors already available today: Core i7-870 at 2.93 GHz and Core i5-650 at 3.2 GHz.

Of course, the Core i7-875K centers on Intel’s 45 nm Lynnfield design, offering four cores with Hyper-Threading enabled, Turbo Boost technology, and a shared 8MB L3 cache. The chip’s dual-channel DDR3 memory controller is integrated onto the processor die, allowing it to move lots of data, quickly. According to Intel, the Core i7-875K employs the exact same silicon revision as previously-launched Lynnfield processors.

Base Clock Speed
Unlocked Ratios
Turbo Frequency
Cores / Threads
L3 Cache
Core i7-980X
3.33 GHz
Core, DDR3, Power
Up to 3.6 GHz
12 MB
3 x DDR3-1066
Core i7-875K
2.93 GHz
Core, DDR3, Power
Up to 3.6 GHz
8 MB
2 x DDR3-1333
Core i7-860
2.8 GHz
DDR3 (Up to 1,600 MT/s)
Up to 3.46 GHz
8 MB
2 x DDR3-133395W
Core i5-655K
3.2 GHz
Core, DDR3, Power
Up to 3.46 GHz2/4
4 MB
2 x DDR3-133373W
Core i5-650
3.2 GHz
Up to 3.46 GHz2/4
4 MB
2 x DDR3-133373W

The Core i5-655K leverages the 32 nm Clarkdale configuration, equipped with two physical cores that use Hyper-Threading to address four threads simultaneously. Turbo Boost is again made available, and the shared L3 cache drops to 4MB. Clarkdale sees the integrated memory controller moved off-die and onto another piece of silicon on the same package, which also houses onboard graphics. As expected, AES-NI acceleration makes a return here.

Because both processors center on Intel’s LGA 1156 interface, you’re still limited to 16 lanes of on-package PCI Express 2.0 connectivity, potentially limiting the multi-card flexibility of these processors in a gaming rig. But we’re going to be testing with a single Radeon HD 5970 today. And for that dual-GPU board, 16 lanes is just the ticket…

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  • With the unlocked multis, is it possible to set the turbo multi and regular multi independantly?
  • Quote:
    It was definitely ridden hard and put away wet.

    What does that even mean? Is it a metaphor for sex?
  • mi1ezWhat does that even mean? Is it a metaphor for sex?

    No, it's a reference to horses.
  • 180446 said:
    No, it's a reference to horses.


    That makes sense...
  • When overclocking phenomX6, why turbocore is enabled? That is not good for OC. And on intel you disable that. Sorry for bad english
  • well this thas made life of p2 x6 tough.
  • Intel Core i7-875K $342 plus $75 socket 1156 motherboard = $420
    AMD Thuban 6core Phenom II X6 1055T plus $50 AM3 motherboard = $249

    I'll save my $200, overclock the AMD Thuban and get within 5 percent of Core 17 875K's performance. IMO, the AMD Thuban is still a better value and the price for i7 875K are for those buying the hype and bragging rights.
  • HundredIslandBoy:
    dusnt the x6 thuban cost abt $316??
  • I don't know why Chris Angelini was suprised by the SKUs chosen - why on earth would Intel make the whole of the i7 9xx lineup redundant by unlocking a 920 - thereby removing the need to buy the 940/950/975? The point is that they release these chips to compete with AMD, but you still have to spend the big bucks on an i7 Extreme to get the ultimate performance & full speed QPI link. One point always seems to be missed in these "cheap" overclocking arguments - buying a cheap motherboard is not an option because you need very good voltage regulators & heatsinks to deal with increased speeds. As is usually the case, if you want speed for games then buy a mid range CPU and spend the extra cash on the graphics card /RAM for a better matched system.
  • Interesting. I would like to see both, i5 655k and i5 750 in action to see who delivers the best performance. No wonder i7 875k is a beast
  • 150478 said:
    HundredIslandBoy: dusnt the x6 thuban cost abt $316??

    The 3.2 Ghz Thuban cost $299. The Thuban X6 2.8 Ghz 1055T costs $199 and easily overclocks to 3.4 Ghz and higher.
  • Mate. I would never buy a $50 motherboard with serious overclocking in mind. Unless I was cheap
  • 317169 said:
    Mate. I would never buy a $50 motherboard with serious overclocking in mind. Unless I was cheap

    Ironic. Most overclockers overclock to add value, squeeze out performance starting on budget CPUs and budget motherboards. Serious overclockers probably look towards pricier Intel platforms since there's more headroom.
  • reported