Intel Core i5 2500K review

Impressive performance for the money, but not without its flaws

IN RECENT TIMES Intel’s biggest jump in performance was when the company moved from the Netburst architecture to the Core 2 architecture, a move that wasn’t repeated when the company moved to Nehalem. Today we’ll take a closer look at Sandy Bridge and without giving away too much; we can tell that it offers an impressive performance boost, although not in every single category.

Editor’s note: Additional Sandy Bridge coverage on it’s way.  Overview, Disappointment, Linux

Let’s start with one of the biggest controversies about Sandy Bridge, the lack of overclocking. Some years ago Intel decided that selling multiplier unlocked CPUs was a bad idea, as some unscrupulous people started to re-brand CPUs, selling cheaper models for more money. This was a big no-no in Intel’s book, but in a way this ended up being a good thing as bus speed overclocking took off and developed into a huge hobby for many a computer user. It’s also been a popular way to get some extra performance out of your system for free.

Then late last year Intel introduced its first K series CPUs which had unlocked multipliers, as well as unlocked bus speed, although these were dual core models and demanded a price premium over the regular CPUs and never really took off, as there wasn’t any real need for them. Enter Sandy Bridge and things have changed, as Intel has now locked down the bus speed, or BCLK as it’s known these days and it’s stuck at 100MHz and we’ve heard reports that some CPU’s won’t even boot at 100.3MHz, although we have as yet to see this for ourselves. This means that you’re stuck with one of two options, buy a K series processor, or give Sandy Bridge a miss and go with the LGA-1366 platform, at least if you’re interested in any kind of over overclocking.

A CPU with an unlocked multiplier is much easier to overclock in many ways, as you just keep increasing the multiplier until you reach whatever limit the CPU will accept, a boon for the casual overclocker, but not a popular move with enthusiasts. The problem is that not all CPUs are equal and some barely go beyond 4GHz while others reach well over 5GHz. It’s a bit like playing the lottery, although overclocking has always been a game of chance, but now it’s more dependent on the CPU than ever before and the motherboard manufacturers will have a hard time selling their overclocking friendly motherboards, as there is very little they can do to affect the overclocking potential of the CPUs.

Oddly enough, Intel has left the graphics multiplier unlocked on all CPUs, not just the K series. This means that you can try to squeeze some extra graphics performance out of your CPU if you’re so inclined. It’s worth noting that this only applies if you’re using an H67 motherboard and from our quick testing, it doesn’t seem to make a huge difference in terms of performance.  It appears that Intel’s graphics architecture is just too limited to benefit in any great way by just pushing the multiplier up. That said, it does gain some performance and it doesn’t appear to have any negative effects to the overall performance of the system.

The biggest benefit of Intel’s new graphic solution is what Intel calls Quick Sync Technology, which allows the GPU to encode/transcode video files. As you’ll see in the benchmarks, it offers a very impressive performance boost, but is currently of limited use as it only works with a select few applications. However, Intel is working with a wide range of software companies to get this feature implemented into their software. The big downside of Intel’s Quick Sync Technology is the fact that it only works on H67 motherboards and only if you’re using Intel’s integrated graphics. This alone suggests that many a user is never going to reap the benefits it has to offer.

Another new feature of the H67 chipset, while we’re on the subject, is the option to enable its display outputs alongside a discrete graphics card. However, there are some limitations here, as each display device is limited to two displays, so if you have say an AMD graphics card with support for five displays, you’re already better off using that than trying to mix and match the two. On the other hand, this makes for a very affordable multi-display option, but even in this mode, Intel’s Quick Sync Technology is disabled.

We’d also like to take the opportunity to point out that the H67 chipset is limited to using DDR3 1333MHz memory at the most, while the P67 chipset supports speed of 1600, 1866, 2133 and potentially even faster speeds. Do note that 2000MHz modules aren’t supported which might cause some problems for those upgrading from older platforms. Again, not a very logical offering from Intel and there isn’t all that much the motherboard manufacturers can do about it either, as least not that we’ve seen.

This review will take a closer look at the Core i5 2500K processor and now that we’ve gotten some of the finer points over, let’s see what’s on offer in terms of performance. For those interested in the nitty-gritty technical details, please have a read through Charlie’s more in-depth piece on what’s new in Sandy Bridge, as this review will focus mainly on the performance advantages in Windows 7. For those still set on running Windows XP, the good news is that Intel will offer drivers for this platform, as well as for Windows Vista of course.

During the time we’ve been benchmarking both the 2500K and its faster sibling the 2600K – which will get its own review shortly – one thing that has been apparent is that Intel has done more than just increase the clock speed. In many applications we’re seeing a modest performance increase, while in others it’s a massive jump in performance, especially anything video related. For comparisons sake we grabbed a Core i5 750 and overclocked it to 3.33GHz, albeit on a 166MHz bus, as this was the closest we could get in terms of an apples to apples comparison of raw CPU performance.

For the benchmarks we used 8GB of Corsair Vengeance DDR3 1600MHz memory with a latency of 9-9-9-24, an Intel 160GB X25-M SSD, a Sapphire Radeon HD 6870 graphics card, an Akasa Freedom power 750W PSU and an Akasa Nero 2 CPU cooler. For these specific tests we also used the Intel DH67BL H67 chipset motherboard and the DP67BG P67 chipset motherboard. We’d like to take a second here to thank the companies that provided the test equipment for this and the following reviews that we have coming of the Sandy Bridge platform.

So let’s start with a benchmark that is somewhat controversial, but that gives an indication as to the real world performance of Intel’s latest CPU generation, Sysmark 2007. For those not familiar with Sysmark, the quick rundown is that it consists of a range of widely used applications that are performing a set number of tasks in a pre-recorded macro mode and then gives you a number at the end. You can find out more details about Sysmark here. The downside is that it’s a rather old benchmark now with slightly out dated applications, but if nothing else it shows how well older software will run on newer hardware. The Core i7 2500K takes an early lead over the Core i5 750 and note that this is a clock for clock comparison.

Next up we have another benchmark that’s meant to emulate usage of a PC, namely PC Mark Vantage. Here the Core i5 2500K holds a significant lead over the Core i5 750 in just about all of the tests. It’s worth noting that the performance in the memory test isn’t that great for the 2500K when paired up with the H67 chipset and the gaming score is of course lacking somewhat here as well due to the use of integrated graphics. Once again, pop in a graphics card and the performance jumps by a fair bit in most of the tests.

Speaking of graphics, Intel’s new and improved GPU might be better than ever, but it still has a long way to go before it can compete with a decent discrete card and even when you overclock it by pushing the multiplier from 22x to 32x the performance gain isn’t what we’d call huge. In actual frames per second the increase is about 2 FPS in the game tests, not exactly a significant amount. Pair up the 2500K with a graphics card and it outperforms the 750 by a small margin at the same clock speed and by a fairer margin with the 750 at stock. We’re going to take a closer look at the graphics performance in the next few days and hopefully compare to something competitive, as we ran into some problems with an entry level card we borrowed that didn’t want to play nice.

Keeping with the graphics theme for a second, we move swiftly on to the OpenGL test in Cinebench 11.5. The initial drivers Intel provided didn’t want to work at all with anything OpenGL, although a later version resolved this problem. Again, the performance isn’t what we’d call breath taking, but judging by accumulated results, Intel’s new GPU performs about on par with a Radeon HD 2600. Again, overclocking the GPU doesn’t yield any huge benefits. Once again, pop in a graphics card and there’s a clear performance advantage compared to the 750.

In the CPU rendering part of Cinebench 11.5 the 2500K really shines and pulls ahead of the 750 by a pretty solid margin. You’d have to push the old Core i5 750 to at least 4GHz to get even close in terms of performance.

We’re seeing similar results in Povray, although this open source raytracing program doesn’t seem to benefit quite as much from the new CPUs as Cinebench.

Video encoding and transcoding is one of the real strong points of Sandy Bridge, even without the added benefit of Quick Sync Technology. We transcoded a 469MB MTS file from a Canon camcorder into a 8192kbps MKV file using Handbrake which is a multithreaded open source video transcoder and as you can see, there’s about a 30 second advantage to the 2500K over the 750 at 3.33GHz and over a two minute lead compared to the 750 at stock.

If we use an Intel optimised application like Arcsoft’s MediaConverter 7 with Quick Sync support, then things get even more impressive. Even the old Core i5 750 gets a new lease of life as even at stock it takes just under 3 minutes for the CPU to transcode the same video clip. The 2500K is still ahead even at 3.33GHz, but only by nine seconds. Enable Quick Sync acceleration and you’re down to one minute and 23 seconds for that same clip. The good news here is that the final video quality appears to be much sharper than when using an AMD or Nvidia GPU to perform the same task.

Finally we have some power usage figures during some of the various tests alongside with idle at the desktop and peak power draw at boot. For a 95W TDP desktop part the 2500K as seemingly power efficient chip and it’s unlikely to ever hit 95W. The power draws in the chart is for the CPU, memory, Intel H67 motherboard and SSD used for testing the platform. Again, apologies for lack of comparison here, but we didn’t have a similar system on hand, although we’ll be doing some comparisons to the Core i5 750 in a follow-up article.


So how to sum up Sandy Bridge so far? Well, not bad springs to mind, but with some reservations. Pricing ranges from a low of 117 USD for the i3 to a high of 317 USD for an i7, individual retail outlets differing, of course. The Core i5 2500K seems to be the sweet spot processor in the new desktop line-up at $216. That’s only an $11 premium over the standard 2500 processor, but it’s a premium you wouldn’t have had to pay in the past to get the ability to overclock your CPU.

The K series is also a better choice for anyone that intends to use Intel’s new graphics, simply because it’ll offer better performance. We can’t quite figure out why Intel only put its high-end graphics solution into the K series desktop processors and it’s something we’re going to ask them about. We’re hearing rumours that the entry level Pentium models might end up with the 3000 series graphics, but for now, that’s just a rumour and nothing more.

The LGA-1155 platform is looking like a win for your average consumer, as you’re getting a lot of extra performance for your money, especially if you do anything video related. Is it worth the upgrade? Well, if your system is older than a Core iSomethingmeanlingless machine, then yes, but if you’ve bought a system with either an LGA-1156 or LGA-1366 processor, then it really comes down to what you do. As we’ve shown, an overclocked Core i5 750 can almost keep up with the new Core i5 2500K, but not in every respect and we haven’t even looked closer into overclocking Sandy Bridge as yet.

What is clear is that Intel will be alienating some users while gaining others. Sandy Bridge is a peculiar move in many ways and we can’t quite get our heads around some of the decisions Intel has made. The really big question at the end of the day is, will AMD to have something to counter Sandy Bridge with and when will it launch?S|A

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