Intel Core i5-2500K £170
3rd Jan 2011 | 05:01
This latest mid-range processor is a huge leap forwards
Intel Core i5-2500K review: Overview
Note: This Intel Core i5-2500K review also reviews the Sandy Bridge architecture as a whole, as well as the high-end Intel Core i7-2600K processor.
Ready or not, here they come. Intel is rolling out a thoroughly overhauled range of PC processors based on its new Sandy Bridge microarchitecture. Our first taste of the new chips comes in the form of the Intel Core i5-2500K and Intel Core i7-2600K desktop CPUs.
Thanks to the baffling array of chips, sockets and brands, we've barely got to grips with Intel's existing CPU range. Certainly Intel's main rival, AMD, has no answer in outright performance terms to the chips Intel already offers, but the relentless march of technology must go on.
So, ignore the familiar Core i5 and Core i7 branding. These are all new processors and they're ready to roll.
As it happens, Intel could actually do with more powerful and, crucially, more power efficient processors for laptop PCs. Deep down, that's what Sandy Bridge is really about. However, as we'll learn, Sandy Bridge has a lot to offer for the desktop, too, including exciting new features such as a hardware video transcoding engine and much-improved integrated graphics.
At launch, it's not quite a full range of processors. In total, Intel is rolling out 14 new desktop CPUs based on Sandy Bridge under the Core i3, Core i5 and Core i7 brands. Pricing extends from around £75 to £250.
The very top and bottom of Intel's desktop range will remain unchanged. The six-core Gulftown derivative of the Core i7 and the entry-level Pentium chips live on for now. Everything else is effectively for the chop.
With new chips inevitably come new chipsets, but what you might not expect is the new processor socket. Known as LGA1155, it's almost identical to the existing LGA1156. It loses just one pin. Problem is, the two sockets are entirely incompatible.
You cannot drop Sandy Bridge processors into any existing motherboard. Nor can you use any previous Intel processors with Sandy Bridge-supporting motherboards.
Although Intel will absolutely deny it, we believe this change in sockets is unlikely to have been a technical necessity.
Instead, at best, we suspect it represents a disregard for existing customers, and at worst a tactic designed to force whole a platform upgrade rather than drop-in CPU changes.
Unfortunately, the new socket isn't the only dubious new feature that debuts with Sandy Bridge. Intel has also made a fundamental change to the chip's architecture that has killed traditional processor overclocking using the CPU bus stone dead. We'll come to the details later, but the bottom line is that Intel has brought overclocking under strict control.
It's not completely gone, but it's only available where and when Intel allows it.
However, don't let those negatives convince you the new Intel Core i5-2500K and Intel Core i7-2600K chips are stinkers. Compared to their closest equivalents from Intel's existing range – the Intel Core i5-760 and Intel Core i7-870 – the new chips are arguably in a different league.
In fact, even the mighty six-core Core i7 980X isn't safe from Intel's remarkable new Sandy Bridge architecture. It's that good.
Intel Core i5-2500K review: Architecture
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.
Intel Core i5-2500K review: Benchmarks
With every new architecture comes a certain amount of intrigue. Intel's Sandy Bridge brings much higher clocks, but it's also interesting to note how performance compares on a clock-for-clock basis.
To find out, we compared the new Core i7-2600K running at 2.9GHz with Turbo disabled to the old Core i7-870, again at 2.9GHz with Turbo disabled. Also worth noting is the performance of the new video transcoding core and the integrated 3D graphics. In their own way, both are frankly staggering.
Stock clocked benchmarks
Cinebench R10 multi-thread
Intel Core i5-2500K: 39s
Intel Core i7-2600K: 35s
Intel Core i7-870: 46s
Intel Core i5-750: 59s
Intel Core i7-980X: 32s
Cinebench R10 single-thread
Intel Core i5-2500K: 2m 22s
Intel Core i7-2600K: 2m 19s
Intel Core i7-870: 2m 58s
Intel Core i5-750: 3m 17s
Intel Core i7-980X: 3m 00s
x264 HD video encode
Intel Core i5-2500K: 27fps
Intel Core i7-2600K: 35fps
Intel Core i7-870: 28fps
Intel Core i5-750: 19fps
Intel Core i7-980X: 43fps
World in Conflict
Intel Core i5-2500K: 91fps
Intel Core i7-2600K: 96fps
Intel Core i7-870: 78fps
Intel Core i5-750: 75fps
Intel Core i7-980X: 90fps
Intel Core i5-2500K: 18.6GB/s
Intel Core i7-2600K: 18.7GB/s
Intel Core i7-870: 17.3GB/s
Intel Core i5-750: 16.9GB/s
Intel Core i7-980X: 17.8GB/s
Idle power consumption
Intel Core i5-2500K: 125W
Intel Core i7-2600K: 130W
Intel Core i7-870: 115W
Intel Core i5-750: 110W
Intel Core i7-980X: 145W
Peak power consumption
Intel Core i5-2500K: 190W
Intel Core i7-2600K: 215W
Intel Core i7-870: 210W
Intel Core i5-750: 180W
Intel Core i7-980X: 245W
Intel Core i5-2500K: 4.4GHz
Intel Core i7-2600K: 4.6GHz
Intel Core i7-870: 3.9GHz
Intel Core i5-750: 4.1GHz
Intel Core i7-980X: 4.2GHz
Cinebench R10 multi-thread
Intel Core i5-2500K: 34s
Intel Core i7-2600K: 29s
Intel Core i7-870: 30s
Intel Core i5-750: 43s
Intel Core i7-980X: 26s
x264 HD video encode
Intel Core i5-2500K: 32fps
Intel Core i7-2600K: 41fps
Intel Core i7-870: 33fps
Intel Core i5-750: 27fps
Intel Core i7-980X: 51fps
World in Conflict
Intel Core i5-2500K: 98fps
Intel Core i7-2600K: 102fps
Intel Core i7-870: 90fps
Intel Core i5-750: 89fps
Intel Core i7-980X: 94fps
Clock-for-clock comparison (Turbo disabled)
Cinebench R10 multi-thread
Intel Core i7-2600K @ 2.9GHz: 46s
Intel Core i7-870 @ 2.9GHz: 51s
Cinebench R10 single-thread
Intel Core i7-2600K @ 2.9GHz: 3m 5s
Intel Core i7-870 @ 2.9GHz: 3m 28s
x264 HD video encode
Intel Core i7-2600K @ 2.9GHz: 27fps
Intel Core i7-870 @ 2.9GHz: 25fps
World in Conflict
Intel Core i7-2600K @ 2.9GHz: 88fps
Intel Core i7-870 @ 2.9GHz: 77fps
Call of Duty 4 @ 1,280 x 800
Intel Core i7-2600K – HD Graphics 3000: 32fps
Intel Core i5-655K – HD Graphics: 14fps
World in Conflict @ 800 x 600
Intel Core i7-2600K – HD Graphics 3000: 22fps
Intel Core i5-655K – HD Graphics: 8fps
Quick Sync Video transcode engine
720p H.264 encode in software
Intel Core i7-2600K: 45s
720p H.264 encodewith Quick Sync Video
Intel Core i7-2600K: 12s
Intel Core i5-2500K review: Performance
First a quick précis of our review chips. The Intel Core i5-2500K is a quad-core, quad-thread chip with 6MB of L3 cache memory and clocks in at 3.3GHz standard and 3.7GHz maximum Turbo frequency. It's yours for approximately £160 unboxed and effectively replaces both the old dual-core Core i5-655K and quad-core Core i5-760.
A partially locked Core i5-2500 is also available at the same clockspeeds for about £10 less.
The £225 Core i7 -2600K, meanwhile, sports four cores, eight threads, 8MB of cache as standard and Turbo frequencies of 3.4GHz and 3.8GHz respectively. It slots in approximately where you would previously have found the likes of the Core i7-870 and Core i7-875K processors in the price list. Again, there's also a marginally cheaper Core i7-2600 alternative that lacks the fully unlocked multiplier.
With all that logged away, it's time for some performance analysis. In a word, these chips are stunning.
At stock clocks, the new Core i5-2500K comprehensively blows away an old Core i7-870. Put another way, the new mid-range chip hammers the old high-end offering. It's literally faster in every benchmark including video encoding, gaming and professional rendering and sometimes by a margin of over 10 per cent. As for the comparison to the old Core i5-760, it's brutal. The new chip is as much as 30 to 40 per cent quicker.
Unsurprisingly, then, the new Core i7-2600K absolutely hoses its progenitor, the Core i7-870. We're talking 25 to 30 per cent more performance absolutely, positively everywhere.
If that wasn't astonishing enough, the i7-2600K actually gives Intel's mighty Core i7-980X six-core flagship processor a real scare. The 980X is, for instance, only about 10 per cent quicker in the Cinebench rendering test and 20 per cent faster in HD video encoding. But it's slower for gaming.
Remember, the i7-980X is a £750 processor.
If you're wondering where the performance gains come from, much is down to increased clockspeeds, but the new processors would still be 10 per cent quicker even running at the same frequencies. Somehow, Intel has made the fastest CPU architecture on the planet significantly faster.
As for overclocking, the news only gets better. Our i5-2500K hits the wall at 4.4GHz, while the i7-2600K motors on to 4.6GHz. That's courtesy of an air cooler. It's silly numbers, frankly.
As if that wasn't enough, the Quick Sync Video hardware transcoding engine adds yet another dimension. Using a special build of Cyberlink MediaShow Expresso, it's possible to compare video encoding with and without the transcoder enabled. Our test video is crunched in 45 seconds in software mode. Flick the switch on the transcoder and it drops to just 12 seconds. Bonkers.
Finally, there's the performance of the new Intel HD Graphics 3000. Here again, it's a story of massively improved grunt. Put simply, it's over twice as fast as the previous Intel HD graphics and massively quicker than any other integrated solution. It's genuinely up to the task of playing older games such as Call of Duty 4 at decent detail settings.
Newer titles, however, require lower resolutions and defenestrated eye candy.
Intel Core i5-2500K review: Verdict
We'll make no bones about it. Intel's latest processors present us with a major headache. On the one hand, there's a hell of a lot we don't like about the Intel Core i5-2500K and Intel Core i7-2600K. All of which has to do with what we believe are probably silly marketing decisions, not engineering issues.
We don't like the fact that Intel has locked down proper overclocking to certain models. We hate that Intel has limited the faster HD Graphics 3000 integrated 3D core to these two K series processors. We're thoroughly cheesed off that the new chips require a new socket, chipsets and motherboard.
And we're borderline homicidal with rage regarding Intel's ludicrous branding scheme.
But here's the thing. In simple CPU performance terms, the Intel Core i5-2500K and Core i7-2600K are staggering. They overclock like the clappers. The integrated graphics is way better than anything before and the transcode engine threatens to annihilate the very idea of running some software on discrete graphics chips before it's even taken hold.
They're so good, in fact, they make nearly all of Intel's supposedly high-end chips for the LGA1366 socket instantly redundant. Bloomfield-based quad-core Core i7 processors are toast. Even six-core Gulftown Core i7s look marginal.
Put simply, these new chips bring massive performance to a lower price point than ever before. How can you argue with that?
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