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Review: Intel Core i7 875K and Core i5 655K - unlocked chips for enthusiasts

by Tarinder Sandhu on 28 May 2010, 05:00 3.0

Tags: Core i7 875K, Intel Core i5 655K, Intel (NASDAQ:INTC)

Quick Link: HEXUS.net/qayis

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The K Club

Both overclocking-orientated chips are from Intel's Lynnfieldrange, based on an LGA1156 form factor. Learn more about the architecture underpinnings here.

Model number Cores/threads Clockspeed Turbo Boost  Process Cache IGP Interface Memory controller
Official memory support
TDP
Socket Price (as of today)
Core i3 530 2/4 2.93 N/A 32nm (Clarkdake) 0.5MB L2
4MB L3
Yes DMI Dual-channel DDR3-1,333 73W LGA1156 £95
Core i5 650 2/4 3.33 3.46 32nm (Clarkdale) 0.5MB L2
4MB L3
Yes DMI Dual-channel DDR3-1,333 73W LGA1156 £160
Core i5 655K 2/4 3.33 3.46 32nm (Clarkdale) 0.5MB L2
4MB L3
Yes DMI Dual-channel DDR3-1,333 73W LGA1156 £200?
Core i5 750 4/4 2.67 3.20 45nm (Lynnfield) 1MB L2
8MB L3
No DMI Dual-channel DDR3-1,333 95W LGA1156 £150
Core i7 860 4/8 2.80 3.46 45nm (Lynnfield) 1MB L2
8MB L3
No DMI Dual-channel DDR3-1,333 95W LGA1156 £230
Core i7 870
4/8 2.93 3.60 45nm (Lynnfield) 1MB L2
8MB L3
No DMI Dual-channel DDR3-1,333 95W LGA1156 £420
Core i7 875K
4/8 2.93 3.60 45nm (Lynnfield) 1MB L2
8MB L3
No DMI Dual-channel DDR3-1,333 95W LGA1156 £300?
Core i7 920 4/8 2.67 2.93 45nm (Bloomfield) 1MB L2
8MB L3
No QPI Triple-channel DDR3-1066 130W LGA1366 £170
Core i7 975 EE 4/8 3.33 3.60 45nm (Bloomfield) 1MB L2
8MB L3
No QPI Triple-channel Unlocked (1,600+) 130W LGA1366 £785
Core i7 980X EE 6/12 3.33 3.60 32nm (Gulftown) 1.5MB L2
12MB L3
No QPI Triple-channel Unlocked (1,600+) 130W LGA1366 £850

Recap

We've added in select processors from Intel's desktop Core i3, i5, i7 8xx, and i7 9xx ranges. The Core i3 5xx and Core i5 6xx chips have dual-core CPUs and integrated graphics on the same package, made possible by a move to a 32nm process.

Core i5 7xx and Core i7 8xx chips also share the same form factor, LGA1156, and offer quad-core processing, albeit with no Hyper-Threading on the Core i5 750. The Core i7 9xx remains the standard bearer, itself headlined by the six-core 980X. Phew!

What's new with K?

Core i5 655K looks identical to the Core i5 650 in our table, and it is in terms of meaningful specifications. The only real difference is that the chip has an unlocked multiplier - the ability to change the multiplier up as well as down - accompanied by a higher etail price of around £200.

The Core i7 875K follows suit. Identical to the standard 870 in all but the multiplier, Intel reckons the bonus of being able to choose how the enthusiast arrives at a particular frequency is worth a new chip. Both chips' Turbo Boost features are kept intact, in case you were wondering.

The point?

Let's take the 875K and examine the point of having a completely unlocked multiplier. The regular chip ships with a 22x setting. Most enthusiast-class P55/X58 chipset-based boards will run at a 200MHz BCLK without breaking a sweat. The maths tells us that one will be able to hit 4.4GHz, assuming the chip has the headroom - probably more with a bit of coaxing from chipset voltages.

Appreciating what the best P55 boards are capable of, we reckon that a minimum 5GHz clock-speed (227MHz BCLK) is required to make the most of the upward-unlocked multiplier. Yet pushing an 870 chip to 5GHz-plus requires some heavy-duty voltage and associated cooling.

The enthusiast would like to see a K-series chip on the 860 CPU as it's significantly cheaper than either the 870/875K, but we doubt Intel would entertain such a release because it would make the purchase of a retail-boxed 870 absolutely pointless.

Sweetening the 'K' deal somewhat, the etail price of an OEM 875K is around £300, or £120 less than the retail 870. Intel knows that very few enthusiasts consider a purchase of the £420 '870 - the majority go into SI-built rigs - so there's some obvious merit in the K-designated processor.

Core i5 655K runs with the same base multiplier as the 875K but the etail price of an OEM part - which usually ships with a one-year warranty - is more than a retail-boxed 650's, and we find it hard to fathom the rationale for having it so.

Summary

Intel's two K-series chips both offer a fully unlocked multiplier - the only real hardware difference between them and the non-K models. The 875K is the pick of the duo, arriving with an etail price of £300, representing a significant cut on the retail price of £420.

Now let's head on over to see how they perform.