Buying Guide: Best CPU: the 8 top processors today

CPUs: What you need to know

What CPU is the best for games? What is the best processor for productivity? What is just the hands-down best CPU?

Stick with us people, we've got all you need to know to find out what processor you should be dropping your cash on.

This year could have been one of the greatest ever for PC processing. After an awfully long wait for new high-end chips from AMD or Intel, verily they both delivered. The result could have been, and should have been, a titanic tussle for desktop supremacy.

Even for those who can't afford premium-priced chips – and let's be honest, that's most of us – the knock on effects would have been huge.

Competition not only improves the breed; it also tends to push down prices. Faster chips and cheaper prices for all, in other words.

As it turned out, neither AMD nor Intel's uber-processors were quite what we were expecting.

AMD's new Bulldozer-based FX processors, for instance, haven't exactly torn up the record books for raw computational grunt. Rumours of upcoming respins could translate into improved performance, of course.

For now, the FX is AMD's new top chip and at least offers an intriguing alternative at certain price points.

Intel's latest range topper, the chip known as Sandy Bridge E, has indeed emerged as the hands-down fastest PC processor you can buy, but it's still not the massive leap forward we had hoped for.

Worse than that, it very much looks like it's a case of Sandy by name, sand bagging by nature.

Put another way, we're convinced Sandy Bridge E could easily be much, much faster, if only Intel was facing stiffer competition. With AMD's Bulldozer not delivering, Sandy E's performance has been capped at a level that's merely good enough. Intel has plenty in reserve should AMD's form take an uptick.

If that seems like a grim assessment of the current state of CPUs, the reality isn't all that bad. New CPUs mean new platforms and in turn that makes now a great time to buy into a high-end system while maximising your long-term upgrade options.

Meanwhile, AMD's failure to take the high end by storm means Bulldozer has been dropped right into the heart of the mid-range melee. Since few of us can actually afford Intel's £820 monsters, maybe we only need AMD to keep Intel honest in the midrange. There's only one way to find out.

Is the PC in crisis?

Certainly the unleashing of new CPUs from AMD and Intel has left us all with a pair of crucial conundrums. Can AMD survive the failure of Bulldozer to sock it to Intel? And just how badly is Intel sand bagging with Sandy Bridge E?

If you reckon we're trying some scaremongering, well, think again.

Bulldozer is a big problem for AMD. Quite literally, the new FX processors sired by Bulldozer are very large. Clocking in somewhere between 1.2 and 2 billion transistors, they are twice as complex as any previous AMD desktop CPU.

That's fine if you're slapping the competition around with large benchmark results. If you've got the biggest performing processor, you can attach an equally large sticker price.

As it turns out, however, Bulldozer is struggling to match the performance of Intel chips with little more than a billion transistors.

Frankly, Bulldozer FX doesn't even compare all that well with some of AMD's own chips packing fewer than a billion transistors.

Bulldozer's problems become especially vexing when you dig down into the architectural details. The big idea with Bulldozer is beating Intel at the multi-threading game. Put simply, there are two ways you can add threads to a CPU.

Most obviously, you can drop in more cores, but you can also allow a single core to process more than one thread.

Playing with threads

The latter option is known as simultaneous multi-threading or SMT for short.

Intel has offered SMT for the better part of a decade, dating right back to the Northwood version of the Pentium 4. In fact, the very first Willamette P4 also had Hyper-Threading (HT) support, as Intel calls it, but it was never switched on.

The early P4 flavour of HT was never that impressive.

It duly disappeared around the same time Intel gave up on chasing high frequencies and changed its focus to power efficiency and multi-core processing with the introduction of the Core 2 family.

However, the basic idea was sound and Intel proved just that when it reintroduced Hyper-Threading with the Nehalem architecture in late 2008. Switching on Hyper-Threading boosted system performance by up to 25 per cent.

Critically, however, that performance increase comes at the cost of very few transistors. Intel's Hyper-Threading is all about using existing resources more efficiently, not bolting on more bits.

In that context, the challenge for AMD was to come up with a CPU architecture that met the dual challenge of increasing the thread count without ballooning the transistor count. And all the while it had to do so more effectively than Hyper-Threading.

AMD's solution is the Bulldozer module.

In simple terms, it's a halfway house between bunging in more cores and Intel's 'multithreading lite' in the form of Hyper-Threading.

A Bulldozer module has a pair of integer execution units, each with its own scheduler. But the rest it effectively shared. So, that's just one decode and fetch and a single floating point scheduler feeding a lone floating point engine, albeit composed of dual 128-bit FMACs.

Now, exactly how effective this would turn out in terms of actual multi-threading performance was pretty much impossible to predict. Predictably, AMD said the Bulldozer was SMT done right, inferring that Intel's HT was SMT on the cheap.

Bulldozer's modular design also threw into doubt the very notion of a CPU core. Did a Bulldozer module count as one seriously hefty core? Or is it a sort of dual-core processor lite? Again, only testing Bulldozer would give us the answer.

Bull-dozy

However, one thing that we were certain about was that a Bulldozer-based chip with four modules and therefore four or eight cores – depending on how you look at it – would end up being a lot smaller in size and transistor count than a conventional eight-core processor.

After all, if it wasn't, AMD may as well have produced a full-on eight-core chip without risking any performance losses associated with Bulldozer's shared resources.

So here's the bombshell.

AMD's six-core Phenom II X6 processor packs precisely 904 million transistors. A quad-module Bulldozer FX chip weighs in at a scarcely believable two billion transistors. Now, it's true that the Phenom II X6 has just 9MB of cache to the FX's 16MB, but that alone is not enough to account for all those extra transistors.

The problem for AMD really hits home when you postulate the kind of performance it might have achieved with a straight forward eight-core update to the Phenom II architecture.

Some simple maths suggests it would be both much faster across the board than a quad-module Bulldozer FX and also smaller and cheaper to manufacture. Meanwhile, hypothetical 10- or even 12-core Phenom IIs would probably fit inside Bulldozer's two billion transistor count and not only blow it away, but very possibly give Intel a run for its money, to boot.

Hell, even Intel's mighty Gulftown six-core chips only swallow up 1.17 billion transistors.

Exactly how AMD ended up with a two-billion transistor chip with at best eight cores and at worst just four, we may never know for sure.

However, one theory mooted by former AMD engineer Cliff Maier is that the explanation involves AMD abandoning hand-tuned circuit design. Instead, Maier claims, AMD has shifted to an entirely automated design process. He also says that circuits designed with automated tools are not only 20 per cent bigger than hand or human-tuned circuits, but 20 per cent slower, too.

Whatever the truth, the upshot is that AMD's FX chips measure 315mm2, which is 50 per cent larger than Intel's Gulftown, a chip that easily outperforms the FX and sells for as much as three to four times the price.

Middling AMD

How much this all matters to you and us depends on the time frame you are considering.

AMD has set FX prices that allow it to compete quite well against Intel's middle to higher performing LGA 1155 processors, such as the Core i5-2500K and Core i7-2600K.

That's all fine and dandy for now. We would advise anyone looking for a chip costing between £100 to £200 to give AMD FX a look.

But in the longer term, letting such a big and expensive chip go for comparatively pitiful prices (remember, Intel's top chips go for anywhere between £400 and £820) cannot possibly be sustainable.

Unfortunately, the fall out may already have begun.

AMD recently announced a round of 10 per cent redundancies affecting pretty much every part of its business. Whether AMD as we know it will survive has become a very real question.

In the meantime, what seems very clear is that another failed CPU design will very probably kill the company. From here on in, every significant product salvo must be on target.

If that's the state of play at AMD, it also provides the context for Intel's most recent CPU launches.

We speak of the new Core i7-2700K and the all-new Core i7-3000 series.

The former takes the tried and tested quad-core Sandy Bridge die and merely ups the nominal clockspeed from 3.4GHz for the 2600K up to (wait for it) 3.5GHz. Not terribly exciting, but easy enough to understand. Critically, the 2700K is only around £20 more expensive than the 2600K. So while you're not getting much more performance, you're not paying a lot extra for it, either.

It's therefore the new Core i7-3000 series that's most intriguing, both in terms of what it might do to high-end PC performance and what it says about Intel's current attitude. All Core i7-3000s are based on the new Sandy Bridge E core.

The first big surprise for us was a total core count – it maxes out at just six.

Not only has Intel already been offering six cores on the desktop for nearly two years. It's been flogging server CPUs with up to 10 cores for a while, too.

Okay, those chips sell for several thousand pounds a pop. But at the very least we were expecting Sandy Bridge E to bring eight cores to desktop computing for the first time.

Playing hide the cores

But the really big surprise came when we saw the die plot image provided by Intel.

Like any plot, it showed the functions of each block on the CPU die in broad brush terms. For Sandy Bridge E, that involves a large lump of cache in the middle, cores down each side and uncore kit including I/O and the memory controller above and below.

The difference, however, was a pair of unlabelled blocks, one each side of the cache memory pool. And it was very clear these blocks were disabled CPU cores.

Yup, It turns out that Sandy Bridge E is an eight-core chip after all. We've seen CPUs with disabled cores before, of course. It's one of AMD's favourite ruses, allowing additional processor models to fill niches, reducing the need to spin up multiple chips and minimising the number of processor dies that end up in the bin.

The thing is, Intel has always been a bit sneery about AMD's core-disabled chips, even inferring that it wouldn't lower itself to such cheap shenanigans. But here we are with an Intel chip with disabled cores.

What on earth is going on? Well, in our view, it's pretty straightforward – Sandy Bridge E isn't running in full eight-core mode because it doesn't need to.

AMD isn't even close to challenging Intel at the top of the performance tables.

Meanwhile, thanks to optimisations to Sandy Bridge cores compared with the previous Nehalem architecture, even with the same core count as Gulftown, the new i7-3000 chips have a modest but unmistakable performance advantage.

For Intel, therefore, it makes sense to ship today with six cores, allowing the use of processor dies with broken cores that would otherwise be thrown away.

Meanwhile, should AMD release a revised Bulldozer chip that unexpectedly raises the stakes, Intel can simply flip the switch on the hidden cores and open up the gap once again.

That's all pretty frustrating.

We'd much prefer to see Intel pushing the envelope, not dragging its feet. On the other hand, you could argue LGA 2011 in its entirety is pretty irrelevant to most desktop users, even to most enthusiasts.

However, in a parallel universe where AMD's Bulldozer was putting Intel under serious pressure, it's easy to imagine Intel releasing a six-core processor for the mainstream LGA 1155 socket and placing it at roughly the same £250 price point as existing LGA 1155 chips.

However you slice it, then, we're all paying a little ourselves for AMD's failure to take the fight to Intel.

In that context, now is definitely one of the trickier times to pick your next processor. The new FX chips are certainly competitive at the price points AMD has chosen. But do you really want to buy into a platform – and even a CPU manufacture – with such an uncertain future?

At the same time, the launch of Sandy Bridge E has just made Intel's LGA 1155 platform look a whole lot less attractive.

The problem, as ever, is that Intel's split socket strategy puts the kibosh on the upgrade path. As it stands, there's no significant upgrade path beyond four cores for LGA 1155. That's something that's not even set to change when Intel releases its 22nm Ivy Bridge processors next year.

Overall, then, it's not an ideal situation. There's not a perfect platform among AMD's AM3+ or Intel's LGA 2011 and LGA 1155 options. And as long as AMD struggles, all things chip-related will remain a little uncertain.

It's a complicated process then, buying a new CPU, so what processor is right for you?

We've checked out the best CPU technology available so there's no need to worry, come with us and find out where to put that hard-earned cash.

Processor Reviews

It's definitely not one of the easiest times in processor history to be choosing your next upgrade.

The best you can do is choose your budget carefully, peruse our reviews and benchmark results and choose the socket, platform and CPU that best meets your needs.

Today's PC processors aren't quite as quick or as affordable as they could be, but there are still some pretty effective chips out there in terms of bang for buck.

Intel Core i3-2100 - £95

Take a cheap chip. And clock the living bejesus out of it. This, friends, has long been the path to great PC performance for the pathologically penniless.

Enter, therefore, the Intel Core i3-2100. Like it or lump it, Intel has by far the best CPU architectures today and the feisty little 2100 is part of its latest generation of chips, known as Sandy Bridge.

With an unlocked multiplier, this thing could seriously rock. Without one, it's merely OK.

Read TechRadar's Intel Core i3-2100 review

AMD FX 4100 Black Edition - £100

Consider the AMD FX 4100. We can't be absolutely sure about this without official confirmation, but we reckon it's based on the very same two-billion transistor processor die as the range-topping FX 8150.

The difference is that two of the 8150's four Bulldozer modules have been nuked from orbit.

The best that can be said about this dual-module Bulldozer is that it's not far behind its triple and quad-module brethren in games.

If only they weren't all off the pace.

Read TechRadar's AMD FX 4100 review

AMD FX 6100 - £140

When is a six-core PC processor not a six-core PC processor? When it's AMD's new FX 6100.

Long before AMD released its fancy new FX chips, we had a feeling a fisticuffs was brewing over the definition of what constitutes a processor core. Now the FX has arrived and the gloves are off.

At stock clocks and with the final module hidden, it's not terribly exciting. However, if it turns out that most of all 6100s will happily run with the final module enabled, it might just be worth a roll of the dice.

If that happens, we'll be more than happy to upgrade the 6100's status to buy.

Read TechRadar's AMD FX 6100 review

AMD Phenom II X6 1100T - £150

Little did we, or frankly AMD, know how good we had it with the Phenom II X6 1100T.

Only now, with the release of AMD's all-new Bulldozer architecture and the FX processors it powers, can we truly put what was once known as Hammer into full context.

It's not that far off when it comes to threading. But it also ponies up that little bit more per-core performance that could make the difference between smooth frames rates and the occasional chugging that really spoils the experience.

It's a bizarre thing to be asking, But please, AMD, have another go with the Hammer.

Read TechRadar's AMD Phenom II X6 1100T review

Intel Core i5-2500K - £170

Odd as it is for a CPU that's a year old to still offer the most advanced computing technology available, the Core i5-2500K feels like an old friend.

Of all Intel's CPUs it seems like the most honest, the most straight forward. If you're a keen gamer, it's probably still the fittest for purpose.

Only the higher clocked 2700K has it beaten. That's beyond impressive for a relatively elderly and affordable chip.

Chuck in the ability to go well beyond 4GHz on air cooling and you have an unbeatable package.

Read TechRadar's Intel Core i5-2500K review

AMD FX 8150 - £225

Eight cores. Over 1 billion transistors. A radical modular architecture. 16MB of cache memory. And Turbo clockspeeds north of 4GHz. How could something that sounds so awesome end up so wrong?

One day, the full story of AMD's troubled new PC processor architecture will emerge. It should make for a fascinating tale. After all, the Bulldozer architecture that underpins the FX 8150 must have seemed like a great idea. It's all about balancing threads with cores with a view to delivering the most efficient and effective processor architecture possible.

However, that two billion transistor count makes it very expensive to manufacture, while its disappointing performance puts a limit on the price tag AMD can attach.

And more than anything else, it's just not a great chip for PC gaming.

Read TechRadar's AMD FX-8150 review

Intel Core i7-2700K - £250

The 2700K is the new de facto king of Intel's line of LGA1,155 models. For us, it's the LGA1,155 socket that's really relevant to PC enthusiasts and gamers, not the highfalutin', server-derived LGA2,011 platform and its quad-channel silliness.

The 2700K, then, is the fastest chip any mere mortal is likely to run in his PC any time soon.

Unfortunately, what it ain't is a big step forward over the existing Core i7-2600K.

What'll she do, mister? The answer during our testing and in the context of air cooling and a modicum of extra voltage is an overclocking speed of 4.8GHz.

A very good result, we think you'll agree. But not materially better than you can expect from most 2600K processors. Again, the game doesn't move on.

Read TechRadar's Intel Core i7-2700K review

Intel Core i7-3930K - £499

The Intel Core i7-3960X is a positively preposterous processor. This is the Intel Core i7-3930K and it's not the same chip. Not precisely, anyway.

We've reviewed the 3960X elsewhere and deemed it disappointing, moderately sinister (it's prima facie evidence of Intel carpet bagging in response to AMD's failure to bring out a really quick chip) and largely irrelevant to human existence.

So, here's the best bit. The 3930K costs over £300 less.

OK, £500 is still a big ask. But the difference in price alone is enough to buy a half decent desktop PC or a cheap laptop.

The point, then, is that this cheaper Sandy Bridge E gives you everything the top chip delivers for a lot less money. There's absolutely no reason to spend any more.

We're not completely convinced even this truly means the 3930K is good value for money. But it's still a very fast processor and the chip we'd buy if we had a big budget.

Read TechRadar's Intel Core i7-3930K review

And the best CPU is...

We'll be honest. This isn't quite the CPU super we'd been hoping to bring you.

That's not because we couldn't get hold of the right chips. Au contraire. We've all the latest and greatest from both Intel and AMD. That includes examples of epic new high-end architectures alongside much more modest chips and some old favourites in between.

No, the reason why it's not quite the test we were planning is simply because AMD and Intel's latest salvoes in silicon didn't turn out how we were expecting. Both disappoint but for very different reasons.

Ultimately, the biggest bummer is AMD's failure with the new Bulldozer FX chips.

They aren't entirely without merit. The two cheaper chips, the six-thread FX 6100 and quad-thread 4100, will be particularly interesting if it turns out that most buyers are having success re-enabling the hidden cores.

Instead, it's the FX's failure to put Intel under any meaningful pressure that's most damaging and in turn explains why Intel has been able to be so very conservative with its own processors.

The new six-core Core i7-3930K is undoubtedly a very fast CPU. But it would be even faster with the final two cores enabled. And we can't see any reason why Intel wouldn't do so.

Apart from the simple fact that the 3930K has no direct competition, that is.

We smell something similarly fishy wafting forth from the new Core i7-2700K. A clockspeed bump of 100MHz is barely worth the bother. But it's enough to give Intel a new product to sell and there's nothing AMD can do about that. It simply doesn't have a product capable of forcing Intel's hand.

All of which means the two most interesting processors here turn out to be the oldest, too.

More than anything, AMD's six-core Phenom II X6 1100T proves the folly that is Bulldozer. It's much quicker per core and it's not that far behind in multi-threading.

In the context of a transistor count that's half as big as Bulldozer, that's ridiculous. The 1100T is a chip that could always make an argument for itself, but we didn't expect Bulldozer's arrival to make it look even better.

Thus by process of elimination, you know what's coming next.

That's right, our winner once again is our old favourite, the Core i5-2500K. Like the Phenom II X6 1100T, the arrival of disappointing new products has only served to enhance the appeal of the 2500K.

It's not absolutely perfect. It would take Intel to flick the switch on Hyper-Threading for that to be true. We all know that's not going to happen.

It's therefore not the ideal chip for heavy multi-threaders including video encoding enthusiasts (with the possible exception of those who are happy with Quick Sync's restrictions).

For everyone else, and especially for gamers, the 2500K remains the champion chip it always was.

Buy one and we guarantee you won't regret it.