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Intel Core i5-6600k

Intel Core i5-6600K (Skylake) review

Our Rating :
Price when reviewed : £228
inc. VAT

Modest CPU and GPU gains over the previous generation, but Skylake is as future-proof as it gets right now


Socket: LGA 1151, Cores: 4, Frequency (boost): 3.5GHz, Integrated graphics: Intel HD Graphics 530


Intel’s Tick-Tock processor development timeline took a bit of a tumble with Broadwell, at least on the desktop. While shrinking from Haswell’s 22nm manufacturing process to 14nm mostly resulted in better power efficiency and extended battery life in laptops, performance gains on desktop were rather modest. Throw in the fact that the desktop chips were released very late and most PC builders and manufacturers didn’t bother with it. With Skylake, it’s Intel’s chance to make amends.

Skylake is a Tock, an architectural redesign for improved performance and additional features, built on the same 14nm manufacturing process as Broadwell. This is partly why you won’t be able to use Skylake processors in existing LGA1150 motherboards. Instead, the new 6th-generation CPUs use the new LGA1151 socket, meaning you’ll need to buy a compatible motherboard to pair with it. Value-oriented H170 boards will be arriving later in the year, but high-end users, gamers and overclockers will be more at home with the premium Z170 chipset.

Intel Core i5-6600K front lid

Indeed, the first two Skylake CPUs will be enthusiast-grade, fully unlocked chips designed specifically for Z170. The top-end Core i7-6700K has Hyper-Threading, meaning its four physical CPU cores appear as eight logical cores within Windows to give a boost to heavily multi-threaded applications. The Core i5-6600K doesn’t use Hyperthreading, but otherwise the two quad-core chips are very similar. The 3.5GHz i5-6600k has a maximum Turbo frequency of 3.9GHz out of the box, with 6MB of level 3 cache, while the i7-6700k typically runs at 4GHz and turbos to 4.2GHz, with 8MB of L3 cache. We’ve looked at the former for this review, as it will be the most sensible choice for most users, striking the best balance between value and performance.

Beyond mere clock speed increases, the biggest changes from the previous generation are under the lid. The on-chip memory controller now supports DDR4 memory, although it still retains a DDR3 controller, so that motherboard manufacturers can make boards compatible with 1.35v DDR3L RAM if they choose. The fully integrated voltage regulator (FIVR) introduced with Haswell is gone, meaning users now have complete control over voltages through the BIOS if their motherboard manufacturer allows it. The chipset also supports up to 10 USB3 ports and has more PCI-Express 3.0 lanes, which can be split multiple ways depending on whether you want to run multiple graphics cards. More exciting is the addition of U.2 support for NVMe storage, which promises to be significantly faster than the traditional SATA interface.


According to Intel, Skylake should provide around a 10% performance boost over a one-year old PC running a ‘Devil’s Canyon’ Haswell refresh-based processor, a 20% increase over a two-year old Haswell-based PC and a 30% boost over an Ivy Bridge-based system. This sliding scale should be of great interest to anyone still running a Sandy Bridge CPU – the i5-2500K has aged terrifically and can still hold its own today, but Skylake might finally be the chip to encourage these people to upgrade.

Our 4K multimedia benchmarks didn’t quite validate Intel’s claims, with an overall score of 113 outpacing the 100 achieved by our Core i5-4670k Haswell-based reference system suggesting a slightly smaller increase overall, although performance varies depending on the task. In the single core image editing test, for instance, a score of 117 is more closely in line with Intel’s predictions. This is also faster than any AMD processor currently available, save for the ludicrous FX-9590 – a 4.7GHz quad-core chip with a thermal design point (TDP) of 220W, which is practically unusable without serious water-cooling. It also lacks any kind of integrated graphics, putting it at a disadvantage to the Skylake platform if you don’t plan on buying a graphics card.

Intel Skylake processor benchmarks - image editing

^ As expected, Skylake has the edge over anything AMD has to offer in single core-optimised tasks

Intel Skylake processor benchmarks - video editin

^ The octa-core FX-9590 takes the edge in video editing, but requires far more power to do so. Clock for clock, Skylake is far more efficient 

Intel Skylake processor benchmarks - multitasking

^ Despite having four more cores, the FX-9590 takes a back seat to Skylake in our multitasking test

Intel Skylake processor benchmarks - overall

At stock speeds you can expect a minor increase over like-for-like Haswell CPUs, but considering this is a multiplier-unlocked ‘K’ edition chip, we doubt many people will stick with the native 3.5GHz.


Although we doubt many people would buy a multiplier unlocked processor and not pair it with a dedicated graphics card, the Core i5-6600K’s onboard Intel HD Graphics 530 is significantly better than previous generation integrated GPUs. It runs at a stock 350MHz, but can Boost to 1,200MHz when required for 3D games.

The Haswell-based i5-4670K could only manage 32.3fps in Dirt Showdown at 1,280×720 with 4x anti-aliasing and graphics quality set to high, but the i5-6600k managed 45.3fps. This score outpaced AMD’s FM2-based A10-6800K, which produced 42.6fps, but the FM2+ based A10-7850K was still faster with a 52fps average. AMD has historically had faster integrated graphics, but this is a clear indication Intel has now mostly caught up in terms of performance.

^ Skylake is a big improvement over Haswell in terms of graphics, although AMD still has a slight edge

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SocketLGA 1151
Frequency (boost)3.5GHz
External bus100MHz
Level 1 cache4x 32KB
Level 2 cache4x 256KB
Level 3 cache6MB
Supported memory typeDDR4/DDR3L
Power rating (TDP)91W
Integrated graphicsIntel HD Graphics 530

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Intel Core i5-6600K (Skylake) review

Modest CPU and GPU gains over the previous generation, but Skylake is as future-proof as it gets right now

£228 inc. VAT