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Intel Core i7-875K and i5-655K Unlocked
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Date: May 27, 2010
Section:Processors
Author: Marco Chiappetta
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Introduction and Specifications

Once upon a time, not very long ago in fact, Intel vehemently frowned upon overclocking. There were even times leading up to new processor and chipset releases when it was rumored that Intel would bring an end to overclocking altogether. Thankfully, the rumors of overclocking's death were greatly exaggerated and we enthusiasts continue to practice its black magic to this very day.

Intel's distaste for overclocking has obviously dwindled over the last few years, however. Whereas before, all of the company's processors were locked and its motherboards lacked overclocking options.  Now, Extreme Edition processors have unlocked multipliers and Intel motherboards have extensive overclocking tools built-in. It probably helps that Intel's current line-up of processor have massive amounts of frequency headroom left under to hood. But we digress...

Today Intel's takes its acquired taste for overclocking a step further. The company is announcing two new mainstream processor offerings, targeted squarely at overclocking enthusiasts and feature unlocked multipliers. The new Core i7-875K and Core i5-655K are virtually identical to the standard Core i7-870 and i5-650 from a technical standpoint, but with the right motherboard, users of these new K-series chips will be able to alter their multipliers to increase frequencies, without having to run any other part of the system out of spec.

Intel Core i7-875K and Core i5-655K Unlocked Processors
Specifications & Features

Intel Core i7-875K Processor Key Features:

  • Four Core Processing: Runs 4 independent processor cores in one physical packageRuns 4 independent processor cores in one physical package
  • Base Processor Frequency: 2.93 GHz
  • Intel Turbo Boost Technology:  Dynamically increases the processor frequency up to 3.60GHz when applications demand more performance.  Speed when you need it, energy efficiency when you don’t.
  • Intel Hyper-Threading Technology: 8 threads provide unprecedented processing capability for better multi-tasking and threaded applications. Do more with less wait time.
  • Intel Smart Cache: 8MB of shared cached allows faster access to your data by enabling dynamic and efficient allocation of the cache to match the needs of each core significantly reducing latency to frequently used data and improving performance.
  • Overclocking Enabled: Core (Turbo) and DDR3 ratios are unlocked for ease of overclocking
  • Integrated Memory Controller: Supports 2 channels of DDR3-1333 memory with 2 DIMMs per channel. Support for XMP memory.
  • Chipset/Motherboard Compatibility: Compatible with all P55, H57 and H55 chipsets. See your motherboard manufacturer for support details for these processors

Intel Core i5-655K Processor Key Features:

  • Dual Core Processing:  Runs 2 independent processor cores in one physical package
  • Base Processor Frequency: 3.2 GHz
  • Intel Turbo Boost Technology:  Dynamically increases the processor frequency up to 3.46 GHz when applications demand more performance.  Speed when you need it, energy efficiency when you don’t.
  • Intel Hyper-Threading Technology:  4 threads provide unprecedented processing capability for better multi-tasking and threaded applications. Do more with less wait time.
  • Intel Smart Cache:  4MB of shared cached allows faster access to your data by enabling dynamic and efficient allocation of the cache to match the needs of each core significantly reducing latency to frequently used data and improving performance.
  • Overclocking Enabled: Core (Turbo) and DDR3 ratios are unlocked for ease of overclocking
  • Integrated Memory Controller:  Supports 2 channels of DDR3-1333 memory with 2 DIMMs per channel
  • Chipset/Motherboard Compatibility: compatible with all P55, H57 and H55 chipsets. See your motherboard manufacturer for support details for these processors
  • AES-NI: Provides 6 new processor instructions that help to improve performance for AES encryption and decryption algorithms.


The new Core i7-875K and Core i5-655K are based on the 45nm Lynnfield and 32nm Clarkdale cores, respectively. We covered the main features and capabilities of these two cores at length here at HotHardware in the past, so we won't do the same again here. We would, however, recommend that you take a gander at these two recent articles:

In those two articles, we cover the specifications, features, and performance of both Lynnfield and Clarkdale and well as their companion motherboards and chipsets. Because the Core i7-875K and Core i5-655K are so similar to their locked counterparts, the information in those articles applies here as well.

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Vital Signs and Overclocking

 

Aside from their markings, there isn't anything that physically differentiates the new Core i7-875K and Core i5-655K from other Lynnfield and Clarkdale based processors.




The Intel Core i7 875K (left) and Core i5 665K (right) Side-By-Side -- From The Top and Bottom

As you can see in the images above, the Core i7-875K and Core i5-655K use the same LGA1156 packaging, but the surface mounted components on their undersides are different from each other.

 
Intel Core i5 655K and Core i7 875K CPU-Z Processor Details

Above are a couple of screen captures from the latest version of CPU-Z showing the Core i7-875K's and Core i5-655K's pertinent details. Looking back at our previous coverage of the first Lynnfield and Clarkdale chips to arrive in the lab, it appears that the Core i7-875K uses the same stepping and revision as previous Lynnfield-based Core i7 processors, but the Core i5-655K is based on a new stepping and revision of the Clarkdale chip (5 vs. 2).

Intel K-Series Unlocked Processors Overclocked
Pushing The Limits

 
Overclocked Intel K-Series Processors, CPU-Z Details

This next set of CPU-Z screenshots shows our max stable overclocks using the new Core i7-875K and Core i5-655K processors in an Asus P7H57D-V EVO motherboard, outfitted with a new BIOS that properly supports the chips. Other than their core speeds, what's important to note here is that all of the overclocking gains were achieved by simply increasing the processors' multipliers. By doing so, the CPU frequency is increased, but all of the other components that derive their clocks from the base clock frequency (incorrectly labeled Bus Speed by CPU-Z) are running perfectly within spec. With a good motherboard that has a BIOS specifically tailored for these new K-Series processors, users have complete control over CPU, Memory, and Turbo mode multipliers and can quickly and easily tweak any of their settings.


Core i7 875K Overclocked to 4GHz...


...And the Core i5 655K at 3.9GHz

To overclock the Core i7-875K and Core i5-655K, we first increased each processor's voltage by .15v and then increased their multiplier until our test system was no longer stable. Turbo mode was disabled to prevent any unwanted frequency spikes, but we left HyperThreading enabled. In the end, we hit 3.9GHz with the 655K and 4GHz with the 875K.

At those speeds, using a stock Intel cooler, the 655K idled at around 37'C and peaked at about 67'C under load. The 875K idled at around 44'C and peaked at about 72'C.

Just in case you're wondering how much additional performance was gained by the overclocks, the Core i5-665K had an MT score of 10,459 in the Cinebench R10 benchmark in its stock config, and an overclocked score of 12,126--and increase of almost 16%. The 875K had a stock score 18,659 in the same test, with an overclocked score of 22,361--and increase of about 19.8%. Of course, with overclocking, your mileage will likely vary.

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Performance Quick Take

As we've mentioned, Intel's new K series unlocked processors are virtually identical to their locked counterparts. For the sake of making some quick comparisons though, we ran the new Core i5-655K and i7-875K through Futuremark’s latest system performance metric, PCMark Vantage. PCMark Vantage runs through a host of different usage scenarios to simulate different types of workloads including High Definition TV and movie playback and manipulation, gaming, image editing and manipulation, music compression, communications, and productivity.  Most of the tests are multi-threaded as well, so the tests can exploit the additional resources offered by a dual or quad-core CPU.

Futuremark PCMark Vantage
Simulated Application Performance

As you can see, at their default settings, the new Core i5-655K and i7-875K processor perform just like their locker counterparts. We didn't have a Core i5-650 at our disposal, but in comparison to the i5-661--which has a 133MHz frequency advantage--the new Core i5-655K performs right in-line with expectations. The comparison between the i7-870 and i7-875K, however, is straight-up apples-to-apples, however, and both chips perform at what are essentially identical levels.

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Summary and Conclusion

Performance Summary: Strictly from a stock performance standpoint, the new Core i7-875K and Core i5-665K processors perform exactly like their locked counterparts, the Core i7-870 and Core i5-650. If you're not overclocking and taking advantage of the unlocked multipliers on the new K-Series processors, there's little to differentiate them from the standard Core i7-870 and Core i5-650 other than their higher model numbers.

Intel will be officially launching the new Core i7-875K and Core i5-665K processors during the Computex trade show taking place in Taipei next week, with availability to follow shortly thereafter. If you're wondering how these new processors will be positioned and priced in Intel's line-up, here's the scoop:

The unlocked Core i5-655K will command a $40 price premium over the locked i5-650, which is a bit steep in our opinion, but at under $220 it is still a relatively affordable processor and offers much more flexibility while overclocking than the standard i5-650. The Core i7-875K, despite having an obviously higher price, is priced to move. You're reading the chart correctly--the Core i7-875K will sell for $342, which makes it almost $240 cheaper than the locked Core i7 870. Intel will have to adjust pricing on the 870 eventually, but when it initially arrives the Core i7-875K will be much more affordable than 870. If you've been contemplating the purchase of a Lynnfield-based rig for overclocking, and have the budget to afford the 875K, it is absolutely the processor to get. Flexibility, performance, and competitive pricing--the Core i7-875K has it all.

 

  • Excellent Overclocking Flexibility
  • 875K Priced To Move
  • Strong Performance
  • Price Premium on the 655K

 



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