Intel Core i7-875k and i5-655k processor review

1. Introduction2. The Intel Core i7-875K and i5-655K3. The Intel DP55WG Motherboard4. Overclocking5. Testing Methodology6. Cinebench R10 64 bit7. Cinebench R11.5 64 bit8. KitGuru Photoshop Benchmark V1(4)9. Valve Particle Simulation Benchmark10. Crysis Warhead11. Far Cry 212. Media Playback13. Power Consumption14. Closing Thoughts15. View All Pages

KitGuru has been overclocking since speeds were measured in MegaHz. In all those years, we’ve never seen a chip taken to 5GHz on air. Never. Until now.

After the FX fell to Conroe, Intel has dominated the performance CPU market for many years. AMD’s eggs are all in the Fusion basket and not expected to be hatched until Q2 2011.

However, one valiant design group managed to deliver the Thurban, 6-core Phenom II X6 product range to market (purely as a stop gap). The unlocked Black Edition 1090 went some way to appeasing AMD’s die-hard fan base.

Unfortunately, that launch seems to have stirred a beast. That beast has an R&D budget bigger than the GDP of many small nations. It has a marketing operation that makes ‘wet ice on wet ice’ look sticky. And it has enormous engineering muscle. All of those advantages have been thrown into creating the ‘special K’ edition processors for l33t enthusiasts who want crazy-clocks delivered for meagre-money.

Having spent days testing the Core i5 655k and Core i7 875k in our labs, KitGuru feels confident in saying… OMG.

Unfortunately for AMD, Intel's processors not only offer more computational performance via smaller silicon per clock cycle, its chips also consume less power while doing so.

Intel has the edge. Several edges, from the design stage to final manufacturing. Although, in my opinion, they have also been lax in targeting specific sectors. Relying on a ‘one size fits almost all’ approach. Until now.

As we opened the two little processor boxes, we could almost hear the bell in the background.

Unlocked cores?   Unlocked multipliers?
Wake up Phenom X6.
Ding, ding. There’s a new challenger in the ring.

The Core i5-655k is an unlocked version of the Core i5-650 and the Core i7-875k is an unlocked Core i7-870. These K Series versions are linked to identical core clocks, thermal dynamics and Turbo frequencies as their locked counterparts. The edge however is in the fact that you can adjust the memory and core multipliers on the fly.

Furthermore if we told you the 875k was actually cheaper than the 870k would your ears prick up? No, I am not kidding because the UK pricing is looking to be around £299 inc vat for the unlocked 875k with the locked 870 still costing around £420. While we would expect the price of the 870 to drop soon it just proves that Intel really have taken off the gloves.

With so many processors in the current line up, lets do a little recap to get things clear in our head.

CPU	Cores	Threads	Base core clock speed	Peak turbo clock speed	L3 cache size	Memory channels	TDP
Core i5-650	2	4	3.2ghz	3.46ghz	4 MB	2	73W
Core i5-655k	2	4	3.2ghz	3.46ghz	4 MB	2	73W
Core i5-661	2	4	3.33ghz	3.6ghz	4 MB	2	87W
Core i5-670	2	4	3.46ghz	3.73ghz	4 MB	2	73W
Core i5-680	2	4	3.6ghz	3.86ghz	4 MB	2	73W
Core i5-750	4	4	2.66ghz	3.20ghz	8 MB	2	95W
Core i7-860	4	8	2.80ghz	3.46ghz	8 MB	2	95W
Core i7-870	4	8	2.93ghz	3.60ghz	8 MB	2	95W
Core i7-875K	4	8	2.93ghz	3.60ghz	8 MB	2	95W

Even though the 875K is a Core i7 processor both are socket 1156 and share the same heatspreader and pin schematic.

The Core i7-875K (45nm) is a 95W processor which runs at 2.93ghz and when Turbo Mode is enabled up to 3.6ghz. This is reached via a 133mhz BCLK and 22x multiplier. There is 4x32kb of Level 1 cache, 4x256kb of Level 2 cache and 8mb of shared L3 cache. Intel tolerance state that 1.4 volt is the maximum recommended, but once they get into the hands of extreme overclockers you can be assured this figure will be totally ignored.

The Core i5-655k (32nm) operates at 3.2ghz and up to 3.46ghz in Turbo mode using a 133mhz BCLK with a 24x multiplier. As we mentioned earlier, this also has an unlocked memory controller which is fully integrated offering official support for 1333mhz dual channel modules.

Interestingly, the 655k also features a graphics processing unit which is 45nm and contains 177 million transistors. This graphics processor is designed to operate with the H55/H57 chipsets and has a 900mhz core with Third Generation Shader Architecture and 12 execution units. It also has support for AVC/VC-1 decode which will please media users and offers Noise Reduction with HDMI/Displayport line outs. Additionally Intel offer Dolby TrueHD and DTS HD Master Audio.

As well as the processors on review today, Intel also sent us the DP55WG Motherboard (Warrensburg) which is very competitively priced in the UK – retailing for around £115 inc vat. While Intel never have had a good reputation for overclocking based motherboards I have had great success with them in the past and instead of using a high end Asus or Gigabyte board I felt it was worth a look. We updated the bios to the most recent to ensure we had full support over both processors.

The motherboard is very similar to the DP55KG which is not entirely surprising as they both share the same PCB. Even though this is firmly marketed as a budget enthusiast board It has three wide PCIe slots which offers full support for both Crossfire and SLI with a PCIe x4 slot available, compatible with x16 cards.

There is a POST LED system which is normally found on higher end motherboard and Intel have cleverly introduced a back panel button to access the BIOS configuration if you are trying to recover from enthusiastic, but failed overclocking attempts.

The board has sacrified some components to hit the modest price point however and we have only 4 channel CPU power circuitry unlike the 6 channels on the DP55KG. When you compare this to 10 phase power being offered by ASUS on some of their boards it does seem woefully inadequate. The DP55WG is clearly not designed for ‘hardcore' overclockers, which will make my findings later even more surprising.

The board offers full options for adjusting CPU and memory voltage, which is basically the same as the higher end DP55KG motherboard.

While the higher end KG supports eight internal Sata drives, the WG is limited to six. To be perfectly honest, I really don't think many enthusiast users would have a need for more than two optical drives and four internal hard drives. If you do however, then you need to look elsewhere – this won't suffice.

The board is based on the Intel P55 chipset and offers the following controllers:

• Integrated audio based on 10-channel (7.1+2) Realtek ALC889 HDA codec. This top-end solution supports HD-DVD and Blu-Ray output, offers frontal I/O, optical S/PDIF-Out and S/PDIF-In interfaces on the back panel, an S/PDIF-Out for HDMI-enabled graphics cards.
• Gigabit Ethernet based on the chipset MAC adapter and Intel 82578DC PHY.
• FireWire controller based on Texas Instruments TSB43AB22A (PCI) supporting two ports, one of which is on the back panel.

The lack of jumbo frame support concerned me, however after testing across my own network with a Belkin 16 port gigabit switch I found performance to be very good, if not class leading. A lack of e-SATA support is missed however as I have a big storage drive with this interface. For the price point however it is understandable – these are extras often found further up the price scale.

The audio performance was also very good and I had no complaints when listening to a variety of music through the Razer Mako speakers.

Overall, the board has been relatively simplified when compared with the higher end model however it is around £50 cheaper than the DP55KG … money saved could actually get you a better processor. First however we need to look at overclocking on the next page to see if it is still a viable solution to get the most out of both processors on test today.

Finally, Intels Control Center software package is not supported on the WG board so all our overclocking was handled directly in the bios.

Initially I didn't have high hopes when overclocking with the modest Intel DP55WG motherboard and I already had a standby Asus board waiting in the wings for this page. For those of you who have read our preview posted earlier then you will know that this board really did rock our world.

The only issue with the board was increasing the BLCK – it did not want to go above 133 for us regardless of voltages or any other settings. We actually hosed the Windows 7 64bit OS a few times which was painful.

Using simple multiplers however we were able to get the Core i7-875K to a whopping 4.8ghz.

To achieve this, we used the Noctua NH D14 cooler – or as I lovingly refer to it – ‘The Austrian Sandwich'. We would also like to thank Crucial for sending us over 6GB of their awesome Ballistix Tracer for this review.

This cooler is without a doubt my favourite on the market right now and I have achieved results very similar to good water cooling. It is a brute for sure but the results are unmatched on air and it has a place in my heart now for every serious build I create.

The Intel bioses are a little ‘strange' when compared to a standardised bios from say, Asus. But if you know what settings to change, the results can actually be very impressive. As I mentioned on the last page, the WG motherboard has only a very simple 4 channel CPU power circuitry and Intel themselves recommend to use the higher end board for the 875K. We actually achieved higher overclocks with this Intel board than several others we compared with later.

Forcing the multiplers to 36 we had to increase voltage override to 1.2375V – which translated to around 1.42 when we increased the current limit override and power limit override as well as adjusting the Vreg Droop Control to performance mode. Without the Vdroop at this setting we were limited to just over 4ghz. Idle state was set to high performance. These settings combined with a few others means that the CPU will always stay locked at the 4.8ghz clocks, regardless of how many cores are loaded.

Using the Noctua cooler we recorded idle temperatures of around 35c and load around 87c (compared to 28c idle and 48c load at reference speeds/voltages). Reducing clock speeds to 4.6ghz and correspondingly lowering voltage slightly, we were able to reduce load temperatures by 10c … which is probably a more realistic long term setting, if you are happy losing 200mhz performance. We obviously ignored our instincts and left the system benchmarking overnight at 4.8ghz, partially expecting it to have BSOD'd when we returned …. but we were happy to see the looped tests still running.

Scaling is impressive and clearly the Austrian Sandwich is coping with voltages right on the limit as no throttling is taking place at these insane clock speeds.

Overclocking the Core i5-655K also gave staggering results and although we ran into the same BCLK issues over 133 we managed to hit a multipler of 133×36! This gave us an end result of around 4.8ghz.

We did get the system to boot at 5ghz and it even ran some benchmarks but it would crash when running the Cinebench R11.5 benchmark. It would have been really cool for us to try and promote a 5ghz stable system, but sadly it was not to be.

To achieve this we set voltages to 1.45 and temperatures reached around 79c under extended load. Ambient room temperatures of around 25-26c were maintained.

This translates to around a 1.6ghz overclock when compared to the reference speeds – a staggering result and it shows just how capable the Noctua cooler really is.

Intel Core i7-875k processor
Intel Core i5-655k processor
Intel Core i7-920 Processor
Intel Core i7-980x Processor
AMD Phenom II X6 1090T Processor
AMD Phenom X4 965 Black Edition Processor
Intel DP55WG Motherboard
Asus Rampage Extreme III Motherboard (1366)
Noctua NH D-14 Cooler (Austrian Sandwich)
Silverstone Raven 02 Chassis (fans on full)
Corsair 850W HX PSU
Sparkle GTX285 2GB Video Card

2x2GB & 3x2GB (4GB/6GB) Crucial Ballistix Tracer 1600mhz
LaCie 730 30 Inch Screen
2x WD Raptor HD
1x Intel 160GB SSD
Artic Cooling MX3 Paste

Thermal Diodes
Digital Sound Level Noise Decibel Meter Style 2
Raytek Laser Temp Gun 3i LSRC/MT4 Mini Temp

Windows 7 64 bit Ultimate
Adobe Photoshop CS5 64 bit
Cinbench R10 64 bit
Cinebench R11.5 64 bit
Valve Particle Simulation Benchmark
Crysis Warhead
Far Cry 2
Fraps Professional

All our benchmarks are taken from a series of five results which helps to ensure that any erroneous figures are removed from the final results. All bioses and firmwares are updated, as is Windows 7 64 bit. Obviously when moving between slot 1156 and 1366 processors we need to use a different motherboard (Asus Rampage in this case) so it is hard to directly compare results but we felt it was worth undertaking – just for the sake of being thorough.

Cinebench R10 has since been replaced by V11.5, but many people have a better indication of relative performance by the results from R10 – after all it has been around for years. We will however include R11.5 results on the following page. For those who don't know Cinebench is not just a mere synthetic benchmarking application, it is based on the rendering engine from Cinema 4D.

The CPU test renders a 3D scene photo-realistically while applying performance intensive functions such as area light sources, procedural shaders, Ambient Occlusion and multi level reflections. Especially when used on faster, multi core CPU systems, MAXON CINEBENCH R10 delivers much more accurate results.

The Core I7-980X is way out in front with our results, which would be expected as it costs almost three times the price of the 875K. That said, when we managed to push the 875K to 4.8ghz, the differences narrow considerably and in the real world the difference would barely be noticeable. Well until you decided to overclock the 980x that is!

Cinebench R11.5 is the newest revision of the popular benchmark from Maxon. The test scenario uses all of your system's processing power to render a photorealistic 3D scene (from the viral “No Keyframes” animation by AixSponza). This scene makes use of various different algorithms to stress all available processor cores.

In fact, CINEBENCH can measure systems with up to 64 processor threads. The test scene contains approximately 2,000 objects containing more than 300,000 total polygons and uses sharp and blurred reflections, area lights and shadows, procedural shaders, antialiasing, and much more. The result is given in points (pts). The higher the number, the faster your processor.

The performance of the 980x leads the way by a huge margin, although the performance of the AMD 1090T follows up closely behind. When we crank the speed of the 875K the differences narrow. The extras cores on the 1090T really help to improve Cinebench 11.5 performance for the AMD solution.

When I was in charge of DriverHeaven I wrote a scripted benchmark which was not only used to help users ascertain system specific performance levels but was useful in reviews to accurately measure performance in key areas. Leading tech sites such as Madshrimps, Hardware Canucks, Benchmark Reviews and Hardocp used my benchmark in their reviews also.

This version of the script has been thoroughly tested on Adobe Photoshop CS5 and CS4 and is compatible with Photoshop 7. It is important to document however that different versions of Photoshop give different end results. Adobe have been fine tuning the program over the years and enhancing specific filters and algorithms for better performance (some filters were rewritten during the CS2 time period). This means ultimately that comparing times with users running other versions of Photoshop is not going to give consistent results.

All results were gained from Adobe Photoshop CS5 64bit exe on Windows 7 64 bit ultimate.

KitGuru PS Bench 1(4)	Core i7 920 (4ghz)	Core i7 875k @ 4.8ghz	Core i5 655k @ 4.8ghz
1. Texturiser (1)	1.8	1.6	1.6
2. CMYK	1.7	1.5	1.5
3. RGB	1.6	1.4	1.4
4. Ink outlines	29.9	27.5	27.7
5. Dust & Stratches	2.8	2.6	2.7
6. Watercolor	26.7	24.2	24.4
7. Texturiser (2)	1.8	1.7	1.7
8. Stained Glass	23.3	21.7	21.7
9. Mosiac Tiles	13.5	12.6	12.5
10. Extrude	151.9	146.5	153.2
11. Rough Pastels	12.2	11.1	11.2
12. Smart Blur	95.6	92.5	96.2
13. Underpainting	35.4	33.1	33.2
14. Mosiac Tiles	13.7	12.9	13.2
15. Spherize	2.6	2.5	2.6
16. Palette Knife	22.7	21.5	21.7
17. Sponge	40.2	38.4	40.5
18. Smudge Stick	12.4	12.1	12.2
Total:	486.9	465.4	479.2

The results show how horribly inefficient Adobe Photoshop is with multiple cores, still favouring clock speed over multithreaded performance. We had hoped with CS5 they would finally have rectified this situation but sadly not. The 875K at 4.8ghz has produced the highest ever score in our benchmark suite, by a considerable margin.

The Valve Particle Simulation Benchmark was developed to showcase processing effects which were added to Half Life 2: Episode 2 and upcoming changes to the Valve Engine. This is a very handy way to test performance with a variety of systems as it utilises multi core processing and particle effects.

The Core i7 875K puts in a great showing with the Valve Particle Simulation Benchmark and when overclocked almost catches up to the ultra high end 980x CPU. The i5-655K also puts in a great showing at just under 5ghz.

Crysis Warhead, like the original, Crysis, is based in a future where an ancient alien spacecraft has been discovered beneath the Earth on an island east of the Philippines. The single-player campaign has the player assume the role of (Former SAS) Delta Force operator Sergeant Michael Sykes, referred to in-game by his call sign, Psycho. Psycho’s arsenal of futuristic weapons builds on those showcased in Crysis, with the introduction of Mini-SMGs which can be dual-wielded, a six-shot grenade launcher equipped with EMP grenades, and the destructive, short ranged Plasma Accumulator Cannon (PAX). The highly versatile Nanosuit returns.

In Crysis Warhead, the player fights North Korean and extraterrestrial enemies, in many different locations, such as a tropical island jungle, inside an “Ice Sphere”, an underground mining complex, which is followed by a convoy train transporting an unknown alien object held by the North Koreans, and finally, to an airfield. Like Crysis, Warhead uses Microsoft’s new API, Direct3D 10 (DirectX 10) for graphics rendering.

We test Crysis through the Ice Levels at 1680×1050 with quality settings on high and global settings to DX10/64-bit.

Until the 875K is overclocked the 980X leads the way by a few fps. When we overclock the 875K to 4.8ghz it pulls away by a further 2fps. This obviously shows that Crysis Warhead doesn't fully utilise all the cores on the 980X cpu and instead favours the massive clock speeds of the overclocked 875k CPU.

Far Cry 2 (commonly abbreviated as “FC2 or “fc2″) is an open-ended first-person shooter developed by Ubisoft Montreal and published by Ubisoft. It was released on October 21, 2008 in North America and on October 23, 2008 in Europe and Australia. It was made available on Steam on October 22, 2008. Crytek, the developers of the original game, were not involved in the development of Far Cry 2.

Ubisoft has marketed Far Cry 2 as the true sequel to Far Cry, though the sequel has very few noticeable similarities to the original game. Instead, it features completely new characters and setting, as well as a new style of gameplay that allows the player greater freedom to explore different African landscapes such as deserts, jungles, and savannas. The game takes place in a modern-day East African nation in a state of anarchy and civil war. The player takes control of a mercenary on a lengthy journey to locate and assassinate “The Jackal,” a notorious arms dealer.

Far Cry 2 is still a popular game and the open world environment can be taxing on even the latest hardware available today.

We are running the game in DX10 mode at 1680×1050 with everything set to very high.

As this engine is particular intensive in an outdoor environment we felt it would be interesting to monitor the minimum frame rates and how each of the processors would help to maintain minimum frame rates across the various sections. The overclocked 655k and 875k processors deliver the highest performance with the 1090T X6 Phenom also really delivering a great gaming experience.

Many people will be using their computers not only for gaming and photo editing, but for watching high definition movies. We look at AVATAR Blu-ray performance with the processors on test today first. The mastering on the AVATAR disc is exceptionally high and the video bitrate is pushing through at some of the highest levels we have recorded – sometimes around 35Mbps.

It is rather clear to see that none of the CPU's have any problems with HD Bluray playback. However a large portion of the audience will be more interested to see MKV container performance with High Definition content. We are testing a 1080p rip of the AVATAR Bluray disc – which is streaming from an Intel 160GB SSD Drive. We have disabled GPU acceleration.

MKV performance across the complete range of processors on test today is fantastic. Until we begin to overclock the 980x holds the performance lead. When at 4.8ghz however the 875k takes the lead. Overclocking the 980x even slightly would push this back in favour of the high end part however.

We measured the power draw of our systems at the wall, isolating external devices such as the monitor from the figures.

The 980x sucks in considerable juice taking around 235 watts under load, this however pales in comparison with the i7-875k when we have it overclocked to 4.8ghz – recorded figures are a whopping 275 watts at the socket. When running at default speeds however it requires a more modest 198 watts.

The i5-655k is a much less demanding processor requiring only 138 watts at reference speeds under load and rising to around 155 watts under overclocked conditions.

Intel's Core i5-655k and Core i7-875k have left us thoroughly impressed. You’re getting great performance, without being asked to shell out a small fortune.

At stock speeds, Intel’s Core i7 980 Extreme Edition is still the performance leader, but let's get real, most of us don’t win the lottery, so stop dreaming and focus on what’s real.

When you consider that the retail price for the 875k is just under the £300 mark and then consider that it’s Intel's unlocked beast of a ‘Black Edition', it’s clearly a stunningly good choice. It out-muscles the Core i7 920/930 and it does so with cheaper mainboard and memory options. Compare this chip to the original 870, which was both locked and £120 more expensive, and you can see what a great deal it is.

We had great success overclocking this processor on our Intel reference board and couldn't believe when we managed to get it stable at 4.8ghz, even if it was hitting a toasty 87c under load. I strongly recommend you spend the money on a high end cooler if you want to overclock this processor – and KitGuru recommends the incredible Noctua NH D14 cooler.

Although great value, the Core i7 875k is still a £300 chip. So what about its sibling, the Core i5-655k, which we expect to be a full £100 cheaper – at just under £199?

If Intel hits this price point, then the 655k will be up against the ‘regular’ AMD Phenom II X6 1055T. To make life harder for the X6, that’s also where the Core i7 920/930 chips live. Which are also hard to beat.

While we love overclocking, and had huge success with our engineering review sample, we can't help but feel that a high frequency overclock does not compensate for a lack of cores. In many cases, for pure gaming, this will be a fantastic choice and I can also imagine the Core i5 655k being bought by hardcore overclockers as a secondary toy just ‘to play with' – it has such huge overclocking potential, in the right hands.

It also has great potential for high end media centers, as it runs relatively cool even when overclocked to reasonable levels. Remember, even if you only clock it to ~ 4.4GHz, this little CPU is actually a match for the X4 965 Black Edition, across a range of tasks, including rendering and encoding. It’s hard not to be impressed, especially when you factor in the modest power draw.

In closing, we feel that the Core i5-655k will become a enthusiasts overclocking toy … yep the guys who love to tweak bioses and try and squeeze every mhz of performance from a chip. I had a great time with it over the last week, and managed to keep pushing it further and further with minor bios tweaks. This is part of the reason this review is a little later than planned. I’ve never seen a processor hit 5Ghz on air. Until now.

But it’s the Core i7-875k that really gets me excited, so much so that it’s actually hard to put into words. As you reach 4.5GHz, this processor starts to give the £850 980X a run for its money, in many tasks. The one I had for review was a particularly good overclocking chip and I managed to get it to 4.8GHz, stable, with air cooling alone in a room where the ambient is around 24 degrees. If I was in the market for a processor, this would be my first choice, because for £300 you really are not going to get anything even close to the overclocked performance. Just make sure you budget a little more for the best cooler you can get your hands on. At reference speeds they are solid performers, but the real joy only comes with breaking the 4Ghz barrier and, trust me, it is not hard at all. Pricing is competitive as well.

With Intel’s ‘Special K’ edition chips. Overclocking is no longer a dark art, just crank the multiplier and add a little voltage. Simple as that.

KitGuru says: Core i5-655k is a ‘fun' chip, we had so much fun overclocking it. The Core i7-875k is probably the best value for money processor Intel have released this decade. Crank it !!

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