Intel Core i5-2500K review

In terms of basic layout, the Sandy Bridge architecture that underpins the new Intel Core i5-2500K and Intel Core i7-2600K desktop processors is not a revolutionary redesign. For launch, Intel has cooked up dual- and quad-core derivatives.

All Sandy Bridge processors are based on Intel's latest 32nm production process. Thus, in Intel's "Tick-Tock" jargon, we're talking Tock. In other words, Sandy Bridge is a new architecture on an existing silicon node.

Familiar features such as HyperThreading and Turbo Boost reappear with a bit of spit and polish. Likewise, most of the so-called uncore features look like a carry over. The memory controller remains dual channel with support for DDR3 DIMMs up to 1,333MHz.

As before, the on-die PCI Express discrete graphics interface delivers a total of 16 lanes. Multi-GPU platforms from AMD and Nvidia are supported, but again only in dual-card configuration with eight lanes per card.

Dig deeper, however, and you'll dredge up some seriously significant changes. For our money, one of the most important is the newly integrated clock generator. In operating frequency terms, this change effectively binds the entire platform to the baseclock.

Bump up the baseclock and all core and uncore elements of the chip, including everything from the PCI Express bus to the memory controller and the cores themselves, gain frequency in proportion.

The upshot is that overclocking via the baseclock is no longer a goer. At best you'll manage an overclock in the low single digits above the standard 100MHz frequency. Instead, significant frequency adjustments with Sandy Bridge is done through the CPU multiplier.

If you recall, Intel recently introduced a number of K series chips with unlocked multipliers. Until now, the special Ks didn't make much sense, such was the ease and effectiveness of baseclock tweaks.

However, it now seems clear Intel was preparing the ground for the baseclock-locked Sandy Bridge architecture.

For Sandy Bridge, the overclocking drill goes like this. K series chips are fully unlocked up to a theoretical 5.7GHz while all other Sandy Bridgers are unlocked to the tune of four speed bins. Given the baseclock of 100MHz, that means a maximum overclock of 400MHz for all non-K models.

That's a major reduction compared to the typical 1GHz overclock possible via the bus or baseclock with most existing Intel processors.

Overclocking aside, the other big change with Sandy Bridge involves video processing. For starters, Intel has given its HD Graphics a major kick up the backside. The result, Intel claims, is a more than doubling in performance compared the previous generation of Intel integrated graphics.

Architecturally, the GPU has been has brought completely on-die.

Remember, previous Intel processors with integrated graphics actually contained two separate chips in the CPU package, one chip with cores and cache, the other with graphics and uncore features such as the memory controller.

At launch, all Sandy Bridge processors have on-die graphics. In terms of 3D performance, the detail spec changes include an upgrade from DX10 to DX10.1. However, much of the performance increase comes from the boost in clockspeed from a maximum of 900MHz to a maximum of 1,350MHz, model dependent.

Things get a little more complicated if you further examine the different models. Among desktop variants, only the two K series chips tested here get the full-fat version of the new graphics core with 12 execution units, known as Intel HD Graphics 3000. All other models make do with the 6-unit Intel HD Graphics 2000.

Odd as it may seem, we believe the other chips in the range do actually contain the full 12 execution units. Most likely for marketing reasons, Intel has decided to disable them on some models.

The other big news involving the graphics core is a new video transcoding engine known as Quick Sync Video. It's a dedicated hardware core for accelerating 2D video encoding and it's in every single Sandy Bridge chip. Intel says it delivers at least twice the performance compared with previous architectures encoding video in software, but a little Intel birdie tells us you can often expect much more than that.

Like pretty much every new Intel architecture Sandy Bridge also brings revised vector instructions. This time round, the new instructions are known as AVX and essentially compliment the existing SSE vector instructions.

Oh and, if you care, the new graphics core supports HDMI 1.4 and, in turn, stereoscopic 3D video including Blu-ray 3D.

Finally, regarding the chips themselves, a quick lesson in Intel's new nomenclature is essential.

All Sandy Bridge processors get some kind of 2000 suffix. Core i3-2100 chips are dual-core processors with HyperThreading and are therefore quad-thread. The Core i5-2300, 2400 and 2500 series are a mix of dual-core with HyperThreading and quad-core without HyperThreading.

Meanwhile, the Core i7-2600 series is quad-core with HyperThreading. If that wasn't complicated enough, you have the aforementioned K series chips with fully unlocked multipliers. Then there are T and S series models with lower operating voltages and power ratings.

Overall, it's pretty baffling stuff.

As for motherboards, all Sandy Bridge processors drop into the new LGA1155 socket. It's not compatible with any previous Intel socket. In total, five new chipsets arrive with Sandy Bridge, but only the P67 and H67 are really relevant to consumers.

There's not a great deal to choose between them, but the key differences include support for the integrated graphics core and video out with the H67, while the P67 exclusively gets the latest version of Intel's Performance Tuning application and a few more options in terms of multiplier adjustment.

Another motherboard-related tweak is the introduction of the EFI firmware with all Sandy Bridge boards. Developed by Intel and already used by Apple in all its Mac computers, EFI replaces the traditional BIOS firmware with a much more powerful platform that supports high resolution graphical user interfaces, faster boot times, larger boot disks (over 2TB) and more.