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Intel Core i7-875K And Core i5-655K Battle Beyond 4 GHz
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1. So Many Ways To Exceed 4 GHz

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.

Processor
Base Clock Speed
Unlocked Ratios
Turbo Frequency
Cores / Threads
L3 Cache
Memory
TDP
Price
Core i7-980X
3.33 GHz
Core, DDR3, Power
Up to 3.6 GHz
6/12
12 MB
3 x DDR3-1066
130W
$999
Core i7-875K
2.93 GHz
Core, DDR3, Power
Up to 3.6 GHz
4/8
8 MB
2 x DDR3-1333
95W
$342
Core i7-860
2.8 GHz
DDR3 (Up to 1,600 MT/s)
Up to 3.46 GHz
4/8
8 MB
2 x DDR3-133395W
$284
Core i5-655K
3.2 GHz
Core, DDR3, Power
Up to 3.46 GHz2/4
4 MB
2 x DDR3-133373W
$216
Core i5-650
3.2 GHz
None
Up to 3.46 GHz2/4
4 MB
2 x DDR3-133373W
$176


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…

2. Intel: 4.8 GHz On Air? Sure!

But that’s not the only curveball we’re throwing. It’d really be pointless to benchmark either of these new CPUs at their stock frequencies. Nobody pays a premium for an unlocked processor only to run it at the same speed as a couple of less expensive models. Instead, we’re pushing both chips as far as they’ll go on air (cooled by Noctua’s NH-D14, that is). The point here is to overclock via the unlocked multipliers, testing to see just how much headroom is available from Intel’s 45 nm and 32 nm nodes.

Additionally, we’re adding a pair of Black Edition parts—the Phenom II X4 965 and Phenom II X6 1090T. The two AMD processors are priced at $185 and $310, respectively. Though Intel’s offerings are more expensive ($216 and $342), the quad-core Core i7-875K goes up against the six-core Phenom II X6 1090T fairly well, while the dual-core Core i5-655K takes on the quad-core Phenom II X4.

Right out of the gate, AMD has the advantage on cost, so Intel has to prove itself in performance beyond 4 GHz.

Core i7-875K

Lynnfield’s “limitations” are fairly well-known, so it was hardly surprising to see the Core i7-875K reach a stable 4.13 GHz before exhibiting a bit of instability.

We were actually able to run most tests at 4.26 GHz before determining that this CPU just couldn’t take the heat over the long term. Using Patrick’s Core i5 clock rate guide as a starting point, we got up to 1.5V before backing down and deciding 4.26 GHz just wasn’t going to happen. Naturally, heat was the enemy here, and CoreTemp saw us consistently butting up against the processor’s 99 degree Tj limit. Of course, it didn’t help that the fourth core ran particularly hot, cresting the limit as the other cores were just hitting 90 degrees.

For all testing, Turbo Boost was disabled, giving us a static overclock. Hyper-Threading is left enabled, and Enhanced SpeedStep is on as well.

Core i5-655K

I was frankly most excited to work with the Core i5, a $216 part manufactured at 32 nm and set to run at 3.2 GHz by default. We’ve already had a couple of Clarkdale-based voltage-related fatalities here in the lab, so I wanted to exercise at least some caution. But ambition got the best of me and I ended up testing up to 1.45V—right about where Don lost his Pentium G6950.

Nevertheless, I was able to boot at 4.93 GHz. On air. Without killing the chip. I managed to run a number of our benchmarks at 4.8 GHz, but crashing in 3ds Max 2010, for instance, compelled me to drop another notch to 4.66 GHz. Still, an extra 1.46 GHz isn’t bad (at a reduced voltage of 1.4165V).

Again, Turbo Boost was turned off for this one, with Hyper-Threading and SpeedStep turned on. As with the Core i7-875K, 8 GB of DDR3 memory ran at 1,066 MT/s with 7-7-7 timings. Really, the beauty of these unlocked parts is that you don’t have to worry about modules able to accommodate tons of headroom. Of course, if you have enthusiast-class DDR3, unlocked memory ratios let you scale data rates up and down (though there’s really little reason to go beyond the official 1,333 MT/s these chips support).

3. AMD: Two CPUs At 4 GHz

Phenom II X6 1090T

Unlocked Phenom IIs are far less novel—AMD has been doing this for years.

No doubt, the excitement over seeing Intel follow suit stems from the company’s advanced manufacturing technology, which facilitates the massive scalability we got out of the Core i5-655K.

AMD’s 45 nm process is no slouch, though. The company was able to introduce a six-core processor at the same 125W TDP as previous quad-core models. According to AMD, this is a result of adding low-k dielectric material in the metal layers to reduce capacitance. Low-leakage parts mean less heat—and that’s good for overclocking on air (the high-end guys actually prefer high-leakage parts, since they overclock more aggressively, and dissipating heat using LN2 isn’t really a challenge).

I struggled to get the hexa-core 1090T stable at 4.3 GHz with Turbo CORE enabled. Then it was 4.2 or even 4.1 GHz. At each setting, general instability kept us from finishing testing (and heat wasn’t even the issue, despite voltages of up to 1.525V). At the end of the day, the X6 1090T was dialed in at 4 GHz with a voltage of 1.475V. The screenshot below was snapped before we started scaling back voltage at 4 GHz to minimize power use.

I won't be surprised if this chip doesn't make it to my next processor review, though. It was definitely ridden hard and put away wet.

Phenom II X4 965

Available under $200, the quad-core Phenom II X4 965 makes a good contender for the Core i5-655K (though it’s worth noting you can get a six-core Phenom II X6 1055T for less, as well; we simply haven’t purchased any yet).

Our 125W sample proved just as stubborn above 4 GHz as the Phenom II X6 1090T, despite our oversized cooler, 1.5V+ CPU VID, and 1.25V NB VID. Prime95 simply wouldn’t let this chip dig in at 4.2 or 4.1 GHz. Nevertheless, we were happy to settle down to a 1.4625V setting while retaining stability at 4 GHz.  

And with that, all four of our test subjects were running at 4 GHz or higher and ready for a dash through the gauntlet.

4. Test Setup And Benchmarks
Test Hardware
Processors
Intel Core i7-875K (Lynnfield) 2.93 GHz, LGA 1156, 8 MB L3, Hyper-Threading enabled, Power-savings enabled

Intel Core i5-655K (Clarkdale) 3.2 GHz, LGA 1156, 4 MB L3, Hyper-Threading enabled, Power-savings enabled

AMD Phenom II X6 1090T (Thuban) 3.2 GHz, Socket AM3, 4 GT/s HyperTransport, 6 MB L3, Power-savings enabled enabled

AMD Phenom II X4 965 BE (Deneb) 3.4 GHz, Socket AM3, 4 GT/s HyperTransport, 6 MB L3, Power-savings enabled
Motherboards
ASRock 890FX Deluxe3 (Socket AM3) 890FX/SB850, BIOS 1.40

Asus Maximus III Formula (LGA 1156) P55 Express, BIOS 1706
Memory
Crucial 8 GB (4 x 2GB) DDR3-1066 7-7-7-20 @ DDR3-1333
Hard Drive
Intel SSDSA2M160G2GC 160GB SATA 3 Gb/s

Intel SSDSA2MH080G1GN 80GB SATA 3 Gb/s
Graphics
AMD Radeon HD 5970 2 GB
Power Supply
Cooler Master UCP 1100W
Heatsink
Noctua NH-D14 w/ LGA 1156 and Socket AM3 Brackets
System Software And Drivers
Operating System
Windows 7 Ultimate 64-bit
DirectX
DirectX 11
Platform Driver
Intel INF Chipset Update Utility 9.1.1.1015
Graphics DriverCatalyst 10.4

Benchmarks and Settings

Audio Encoding

iTunes

Version: 9.1.1.12 (64-bit), Audio CD ("Terminator II" SE), 53 min., Default format AAC

Video Encoding

TMPGEnc 4.7

Version: 4.7.3.292, Import File: "Terminator II" SE DVD (5 Minutes), Resolution: 720x576 (PAL) 16:9

DivX 6.9.2

Encoding mode: Insane Quality, Enhanced Multi-Threading, Enabled using SSE4, Quarter-pixel search

Xvid 1.2.2

Display encoding status=off

MainConcept Reference 2.0

MPEG2 to MPEG2 (H.264), MainConcept H.264/AVC Codec, 28 sec HDTV 1920x1080 (MPEG2), Audio: MPEG2 (44.1 KHz, 2 Channel, 16-Bit, 224 Kb/s), Mode: PAL (25 FPS), Profile: Tom’s Hardware Settings for Qct-Core

HandBrake 0.9.4
Version 0.9.4, convert first .vob file from The Last Samurai to .mp4, High Profile

Applications

Autodesk 3ds Max 2010 (64-bit)

Version: 2010 Service Pack 1, Render Space Flyby Scene at 1920x1080 (HDTV)

WinRAR 3.90

Version 3.90 (64-bit), Benchmark: THG-Workload (334 MB)

7-Zip

Version 4.65, Built-in Benchmark

Adobe Photoshop CS4
Radial Blur, Shape Blur, Median, Polar Coordinates filters

Synthetic Benchmarks and Settings

3DMark Vantage

Version: 1.02, GPU and CPU scores

PCMark Vantage

Version: 1.00, System, Memories, TV and Movies, and Productivity benchmarks, Windows Media Player 10.00.00.3646

SiSoftware Sandra 2010

CPU Test=CPU Arithmetic/Multimedia, Memory Test=Bandwidth Benchmark, Cryptography

Games
Crysis
High Quality Settings, No AA / No AF, 4xAA / No AF, vsync off, 1680x1050 / 1900x1200 / 2560x1600, DirectX 10, Patch 1.2.1, 64-bit executable
Just Cause 2
High Quality Settings, No AA / 16xAF, 4xAA / 16xAF, vsync off, 1680x1050 / 1920x1200 / 2560x1600, Desert Sunrise Benchmark, Steam Version
Call of Duty: Modern Warfare 2
Ultra High Settings, No AA / No AF, 4xAA / No AF, 1680x1050 / 1920x1200 / 2560x1600, Second Sun, 450 second sequence, Fraps
DiRT 2
High / Ultra High Settings, No AA / No AF, 8xAA / No AF, 1680x1050 / 1920x1200 / 2560x1600, In-Game Benchmark, Steam Version
5. Benchmark Results: Synthetics

For the most part, Vantage paints a picture we pretty much expected to see. Mainly, the quad-core, Hyper-Threading-equipped Core i7-875K throws down the highest numbers, followed by AMD’s hexa-core Phenom II X6 1090T. The battle between the Core i5 and Phenom II X4 is surprisingly close, considering the significant clock rate disparity.

Reflecting a proclivity for threading, the 3DMark CPU scores are perhaps most interesting. There we see the Lynnfield-based processor score first, followed by the Thuban-based X6. AMD’s Deneb-based X4 snags third, followed closely by the Clarkdale-based Core i5.

6. Benchmark Results: Media And Transcoding

iTunes continues serving one interesting purpose: demonstrating the merits of high clock rates. The 4.66 GHz Core i5 actually finishes our workload first. Because iTunes isn’t threaded, it gains nothing from the chips with four or six cores. As such, it’s a little surprising to see the Phenom II X4 and X6 with nine seconds separating them. More often than not, though, both 4 GHz parts should be on equal footing in single-threaded titles at the same frequency.

We’ve upgraded to the newest version of MainConcept, which shows the Core i7-875K at 4.13 GHz in first place with AMD’s Phenom II X6 1090T close behind. The Phenom II X4 965 takes third, simply outclassing Intel’s Core i5-655K at 4.66 GHz.

HandBrake exploits parallelism, and the six-core Phenom II X6 1090T offers more of it than the quad-core Core i7-875K, despite Hyper-Threading’s influence. Similarly, the quad-core Phenom II X4 965 is faster than the Core i5-655K.

Though DivX is well-threaded, Intel reverses the trend seen previously and takes a lead versus the Phenom II X4 and X6 with the Core i5 and Core i7, respectively. Xvid is not well-threaded, so it’s no surprise to see the higher-clocked Intel processors finishing our benchmark workload first and second.

7. Benchmark Results: Productivity

Our Photoshop CS4 benchmark is threaded, so Intel’s Core i7-875K does well here, as does the Phenom II X6 1090T. The Core i5 and Phenom II X4 are on fairly even footing.

Apparently, 3ds Max isn’t able to exploit Hyper-Threading to the same degree as some of our other tests. AMD’s four-core and six-core CPUs are clearly faster than Intel’s unlocked two-core and four-core models in a head-to-head comparison.

Although the Core i5 and Phenom II X4 nearly tie, Intel’s Core i7-875K takes an undisputed win in WinRAR, a compression app we know to be fairly well-threaded.

Not only is 7-Zip threaded, but it’s also optimized to take advantage of Intel’s hardware-based AES acceleration. That doesn’t stop the Core i5 from coming in last place here, though. Fortunately for Intel, its Core i7-875K running at 4.13 GHz is quick enough to secure a first-place finish, but the Phenom II X6 and X4 aren’t far behind.

8. Benchmark Results: Crysis

At 1680x1050, the resolution least bottlenecked by graphics, Intel’s Core i7-875K really stretches out. And even at 1920x1080, the chip’s first-place finish is commanding. Though far fewer people actually play at 2560x1600 on 30” displays, it’s worth noting that the results even out a lot more without AA turned on, while excessive I/O access makes the 4xAA-based scores inconsistent (the screen alternates from smooth to slideshow-like on the Radeon HD 5970).

The Phenom II X6 doesn’t seem to be a performance-inhibitor, but as we observed in the Phenom II X6 1090T review, the extra cores certainly don’t seem to help for gaming. We’ll see if this trend continues through our other test titles.

9. Benchmark Results: Just Cause 2

With anti-aliasing turned on, all the way through 2560x1600, the quad-core i7-875K turns in the best performance, followed by Intel’s Core i5-655K.

Conversely, with AA turned off, the scores jump around a bit, but remain in a fairly tight range.

10. Benchmark Results: Call Of Duty: Modern Warfare 2

Again we see the Core i7-875K put in a strong showing at 1680x1050 and 1920x1200. By the time we hit 2560x1600, the Phenom II X6 has almost caught up, though all four platforms still deliver more than enough performance for smooth game play.

11. Benchmark Results: DiRT 2

AMD’s CPUs do well here—enough so that it’d be hard to make a recommendation one way or the other based on DiRT’s results alone. Generally, though, the Phenom II X6 1090T seems to come in ahead with 8xAA turned on, which is probably the setting you’d want to use with such a high-end combination of hardware.

12. Power Consumption

As we increase the voltage supplied to hit higher clock rates, the power consumption of these processors increases beyond the specs set forth by AMD and Intel.

Every CPU is different of course, but we generally noticed higher idle power numbers across the board versus past processor reviews with chips running at stock settings. Of course, you have to be careful in comparing this setup to the one used in my Phenom II X6 1090T story, for example. We’re using twice as much memory, a dual-GPU graphics card, and a much more aggressive processor cooler.

Under load, the Core i7-875K uses the most power, followed fairly closely by the Phenom II X6. Even at 4.66 GHz, the 32 nm Core i5-655K is much easier on the energy bill.

13. Conclusion

Drawing conclusions on this one is surprisingly easy. Intel gets major kudos for going somewhere it has never gone before: opening up enthusiast-class flexibility to the folks who don’t have $1,000 to spend on a new CPU.

It wouldn’t be fair to sarcastically toss out a, “way to join the party, Intel.” Remember that once upon a time, AMD only unlocked its $1,000 FX-series chips, too. But getting eclipsed on the performance front encourages creative thinking. The fact that Black Edition CPUs are available under $100 is less altruistic and more strategic.

At the end of the day, it’s all good news for enthusiasts, who now have more choice and more flexibility at price points they can more realistically afford.

…versus Intel

If you’re looking at Intel’s product stack, these new chips (particularly the Core i7-875K) are just what the doctor ordered. I mean, I wouldn’t have ever suggested that a 2.93 GHz Core i7-870 was a good buy at $562 when the 2.8 GHz Core i7-920 was selling for $294. But a Core i7-875K at $342 is at least a little more attractive if you’re using that $562 price point as a reference.

At the same time, an unlocked Core i5-655K at $216 doesn’t sound daunting at all. For a processor that ran stable for us at 4.66 GHz, you couldn’t really ask for sweeter dual-core chip to take the place of Intel’s Core 2 Duo E8500 and E6300 in the annals of overclocking history.

At the same time, we have to wonder why Intel picked the SKUs that it did for K-series honors. Tom’s Hardware’s favorite overclockable Core i7 remains the LGA 1366-based -920 (or -930). Our favorite i5 remains the -750. Either one of those models, unlocked, could have been priced similarly, opening up X58’s PCI Express connectivity at the high-end, and giving enthusiasts a true quad-core LGA 1156 CPU with which to play, even if it’s a more-expensive-to-manufacture 45 nm design.

…versus AMD

And that leads to the inevitable comparison to AMD’s Black Editions.

Versus the Core i7-875K, overclocked, AMD’s six-core Phenom II X6 1090T is generally outperformed at 4 GHz. But it’s also $30 cheaper. It also takes off in heavily-threaded video encoding titles. And it also populates a platform well-endowed with PCI Express 2.0.

While you could easily set the Core i5-655K up against AMD’s Phenom II X6 1055T, we chose the quad-core Phenom II X4 965 instead, which also hit 4 GHz stably. Threaded titles uniformly favored AMD’s offering, while workloads like iTunes gave the 32 nm chip’s insane 4.66 GHz clock the advantage. Again, though, Intel is asking an extra $35 over AMD’s price of entry.

Bottom Line

As enthusiasts, we’ll again emphasize how happy we are to see Intel unlocking processors beyond its Extreme Edition parts.

But despite the excellent scaling you get from the company’s more advanced manufacturing technology, AMD’s Black Edition parts still come across as better values for the money, even when you overclock both parties involved to the limits of stability. With a slight massage to each model's price point, though, this story could easily turn back around and go the other direction.

The K-series chips give Intel significantly more street cred. Here's hoping the product family lives on and expands to include additional enthusiast-class parts.

Follow Chris Angelini on Twitter for updates from the Tom's Hardware lab.

Contest Info

Win A CyberPower Core i7-875K-Based PC Worth $1,499

Intel Core i7-875K CPU
Intel 40GB SSD OS Drive
CoolerMaster 690 II Advanced Case
Asus P7P55D-E PRO Motherboard
4 GB DDR3-1600 Kingston Hyper-X Memory
1 TB Hitachi Hard Drive
Samsung 8x Blu Ray Combo Drive
EVGA GeForce GTS 250 1 GB Graphics Card
800W Power Supply
Windows 7 Home Premium 64 bit
Card Reader, Keyboard, and Mouse

Click here to enter.

Contest is limited to residents of the USA (Excluding R.I.) 18 years of age and older. Contest starts on May 27, 2010 9:00 pm, Pacific Daylight Time and closes on June 10, 2010 11:59 PM, Pacific Daylight Time.

Results will be announced by June 16, 2010.

The information you provide will only be used to contact you in relation to this contest.

YOU MAY SUBMIT ONLY ONE ENTRY. MULTIPLE ENTRIES FROM THE SAME PERSON WILL ALL BE DISCARDED.