Monday, April 20, 2015

Overview of Laptop Processors, April 2015

Recently I've had a few people come up to me asking for advice on buying a laptop. The problem with asking for advice on a laptop is that many are looking for a good budget laptop, and the term "budget" is rather vague. I've spoken with many people over the years, and for some when they say "budget" it's almost the equivalent of saying "free"; others are a bit more sensible in that they're looking at $400 or less, while at the higher end of the definition a budget laptop could go as high as $750. And of course there are plenty of non-budget processors to consider as well.

Given the range of options at the various price points, I wanted to take some time to dig deeper into the laptop market and talk about what processors are available and what sort of performance you can expect from each. The reality as usual is that there are compromises you'll have to make, either in spending more money or giving up performance or features. But since it's important to lay the groundwork for laptop performance before getting into any specific recommendations, I wanted to post this in a separate article.

Making Sense of the Processor Choices

Perhaps the biggest issue with laptops for most users is understanding exactly what you're getting in terms of performance. While performance isn't the only criterion to consider when buying a laptop, the difference between the various processors can have a rather large impact on the user experience. There's this idea today of getting a computer that's simply "fast enough", and there's something to be said for that approach; the problem is that realistically there are at least two classes of processor that are commonly found in budget laptops that simply aren't "fast enough". Here then is an overview of the processors you can expect to find in a modern laptop.

Intel "Atom" CPUs and AMD Mullins/Beema APUs

No matter what anyone tries to tell you about raw performance, I want to be clear: the performance offered by Intel's current Atom processors and AMD's current Beema APUs is not sufficient for most users. Its ironic that Intel at least seems to be banking on users looking at clock speeds and core counts and thinking, "yeah, this should work well enough," as the megahertz/gigahertz wars were largely ended in the Pentium 4 era. The problem is both Intel and AMD now have names that overlap between these slower families and the faster processor families discussed below.

What you need to know in a nutshell is this: even at 2.16GHz (e.g. Intel Celeron N2840), the formerly Intel Atom processors are not as fast as a 1.4GHz Core series processor -- the latter, which we'll cover below, is often twice as fast and not usually that much more expensive. If you want a different perspective on how slow these parts can be, consider that Intel has largely dropped their Atom brand from the laptop market -- they've moved these parts into Celeron and Pentium model names, as Atom has a rightfully deserved bad reputation in the laptop world.

Note that Atom isn't dead, however; Intel continues to use Atom branding for their tablet/smartphone SoCs. The difference is that most of the ARM-based tablet and smartphone SoCs are of a similar speed to Atom, or at least close enough to consider the parts competitive, and they usually run Android -- a far less processor intensive OS than Windows.

AMD for their part is almost worse, as the fastest Beema parts are practically MIA (Missing In Action), leaving only their low power Mullins parts that are intended more for use in tablets. If you see a laptop with an AMD E-series APU, my advice is to just walk away; the faster A4/A6 APUs like the A6-6310/6410 aren't much better on the whole, especially when taking total laptop price into account.

So how do you know if a processor is from Intel's "formerly Atom" stack or AMD's Beema/Mullins family? For Intel, go to ARK and type in the part name; click on the appropriate processor and in the top-right of the product information screen under "Related Products" you should see something that says "Products formerly Bay Trail" or similar. The processors that you want should be from the Haswell or Broadwell families these days. Cherry Trail is the next generation of Atom processors; it adds some improvements and might be a bit better, but until I see benchmarks I'd avoid these as well.

On the AMD side of the equation, figuring out precisely which processor family you're dealing with is a bit more difficult. The APUs that are okay are mostly Kaveri (or Richland in a pinch), with Carrizo due out in the next few months. The APUs to avoid are the Kabini, Temash, Mullins, and Beema parts. The easiest place to determine what part belongs to which family is to just look at the AMD APU Wiki.

AMD Kaveri APUs

The next step up is going to be a bit trickier to define, so for all intents I consider the AMD Kaveri APUs to be at roughly the same performance level as the Intel Celeron/Pentium Core CPUs below. The main difference is going to be in terms of integrated graphics performance vs. pure CPU performance. AMD has better graphics (and better graphics drivers), while Intel offers better single-threaded performance. For a lot of users, I consider the CPU performance to be the bigger factor, though light gaming will fare better on AMD APUs.

The problem with AMD's APUs is that they trim down performance a bit too much for my liking on the lower end models, which means even though the graphics is faster than Intel's equivalent, the APUs still aren't that great for actual gaming. The acceptable settings end up being 1366x768 with low to medium quality to get above 30 FPS, and that's a pretty low bar to clear. Again, I recommend checking out the AMD APU Wiki to determine which specific parts are Kaveri APUs, but if we're looking at budget laptops the most likely candidates are the quad-core A8-7100 and the A10-7300 (I'd give the dual-core A6-7000 a pass, as it's not really much cheaper than the others considering the performance trade off. The FX-7600P is also out as it still hasn't shipped in any laptops that I can find).

Looking at those two candidates, the A10-7300 is only about 5-10% faster in CPU workloads, so the main benefit is the graphics is potentially 50% faster. Since the main draw of the AMD APUs is graphics performance, the A10 is probably the best bet, assuming you can find it in a laptop at a reasonable price. And again, as mentioned earlier, the next-generation Carrizo APU should be out in the June/July time frame, boasting further improvements in graphics and processor performance. If you can wait a bit, it's probably not a bad idea to see how Carrizo fares.

Intel Celeron/Pentium "Core" CPUs

Where things start to get more interesting -- and confusing -- is when we reach Intel's Celeron and Pentium parts that are based on the Core architecture. There are currently three families of processors that are readily available: Ivy Bridge (3rd Generation Core), Haswell (4th Generation Core), and now Broadwell (5th Generation Core). If you're not well versed in the differences between the various Intel products, it can get a bit confusing.

To quickly summarize the differences between the three Core generations, Ivy Bridge was Intel's first 22nm processor, originally launched three years ago. It was a good processor when it launched and performance is still competitive, but the newer Intel processors tend to provide better battery life. Haswell first started showing up about two years ago, and it uses a 22nm process as well. The main benefit of Haswell is power requirements, with some newer techniques to help the processor "race to idle". Broadwell meanwhile has only launched in the tablet (Core M) and Ultra Low Voltage (U-series) parts, starting in December 2014. It's Intel's first 14nm processor, with the biggest gains again coming in power requirements.

With that summary out of the way, my general advice is to forget about anything using an Ivy Bridge processor, and while Haswell is still fine, all things being equal I'd prefer to get one of the new Broadwell processors. In terms of performance, Broadwell-U so far hasn't proven to be much faster than Haswell-U, but battery life is often 15-20% better, and for a laptop that's a tangible benefit. Since prices are at least reasonably close, I'd only go after a Haswell laptop if there's a significant pricing advantage (at least 20% savings).

For the budget minded, there aren't too many laptops with Celeron or Pentium Broadwell processors right now. The Celeron 3205U is currently available in a couple of Acer Chromebooks, and if you're okay running ChromeOS they can be had for under $300. Sadly, the Celeron 3755U isn't currently showing up in any laptops I can find, and the Pentium 3825U is not better. The Pentium 3805U however is currently available in two laptops, a Dell Ispiron 5000 17.3" laptop and a generic brand Eluktro 15.6" laptop. The Eluktro at least has decent specs -- 1080p, 4GB RAM, and 120GB SSD is the base model, but the price is going to push people away as it starts at $600.

Intel Core i3 CPUs

The remaining Intel processors all follow a pattern similar to the above Celeron/Pentium offerings, with the difference being that there's no overlap with the much slower Atom architectures. Somewhat surprisingly, the pricing on Core i3 Broadwell laptops isn't often all that different from the Celeron options, at least when looking at Windows laptops.

I'm going to recommend sticking with the 5th Generation Intel processors at this point, at least for lower priced laptops; the higher performance Broadwell processors haven't shipped yet, however, so outside of the ULV processors you're currently going to have to go with an older Haswell processor... or wait. Since the next wave of Broadwell parts should start showing up in the next month or two, at this point I'd recommend waiting if you don't want a ULV laptop.

Core i3 processors are in many ways similar to Celeron and Pentium parts, but Hyper-Threading is enabled. This allows the dual-core processors to execute instructions from up to four threads simultaneously, and while it won't necessarily make a huge difference in performance for many use cases, it's a welcome addition. Clock speeds are also higher than on the Celeron and Pentium parts, which will further improve performance.

Arguably the most interesting Core i3 processor is currently not in use, sadly -- the i3-5157U is a 28W TDP part with Intel Iris 6100 Graphics, which in theory should provide a decent level of graphics performance (roughly twice as fast as the current HD Graphics 4600/5500). It's not clear if any laptop OEMs are planning to use this processor, so we'll have to wait and see. Two other Core i3 parts, the i3-5015U and i3-5020U, are also not currently in any products that I can find.

Looking at the remaining two Core i3 CPUs, the i3-5005U is available, with Dell currently selling the Inspiron 15 3000 at just $339 with 4GB RAM and a 500GB HDD. Acer has a similarly equipped E5-571 for $460, so the Dell is really a great bargain. There are also Chromebooks using the i3-5005U, but with pricing being higher than some of the Windows laptops, it's a bit of a tough sell. The i3-5010U meanwhile is mostly in higher priced NUCs and laptops, so I'd hold off on that for now. On a related note, last generation i3-4010U and i3-4030U laptops aren't really any better in pricing or features, making them a questionable alternative.

Interestingly, while there are in theory a bunch of non-ULV 4th Generation Core i3 processors, these were mostly ignored by OEMs who felt anyone wanting more than a ULV Core i3 would probably be looking at Core i5 instead. And they're basically right -- the pricing of the i3-4000M laptops basically puts them up against various Core i5 laptops that generally win out in various features.

Intel Core i5 CPUs

What does Core i5 bring to the table compared to Core i3? Mostly, just one thing: higher clock speeds thanks to Turbo Boost. Where Core i3 tops out at a set speed (2.0-2.2GHz for the 15W Core i3 Broadwell parts), Core i5 lets the CPU run at much higher clocks if the right conditions are met. What that means in practice is that for less strenuous workloads, Core i5 can run 30-40% faster than Core i3. The catch is that in some cases the difference may end up being a lot less, like maybe only 10%.

Other than clock speeds, the only other difference is dependent on which model of processor you're looking at -- e.g. i5-4300U includes vPro and TSX-NI where the i3-5005U doesn't (but the i5-5200U doesn't include these either). Note that all of the Core i5 mobile parts are still dual-core processors, unlike on the desktop where Core i5 is quad-core but without Hyper-Threading.

The good news is that prices between the Core i3 and Core i5 laptops are frequently so close that there's little reason not to get the potentially higher performing Core i5 parts. Core i5-5200U laptops start as low as $450 or so, and that's with 8GB RAM (and a slow 1TB HDD). If you want a smaller chassis, however, be prepared to pay a lot more -- 13.3" laptops with the i5-5200U start at well over $600 by comparison. Core i5-5300U is the business alternative, with vPro and TSX-NI, so not surprisingly it's only found in laptops that cost substantially more (e.g. ThinkPad T450s).

There are four other Core i5 Broadwell-U parts, but they're not as widely used (yet?). The i5-5250U and i5-5350U are similar to the above 5200U/5300U, but they have the potential for higher graphics performance as they have 40 EUs instead of 24 EUs. The problem is most of the ULV parts are TDP limited, and with the same 15W TDP I wouldn't expect the added potential to really manifest. As far as I'm aware, these are currently only being used by Apple in their new MacBook Pro Retina 13 and MacBook Air laptops. The i5-5257U and i5-5287U meanwhile are basically the same as the "made for Apple" parts with 40 EUs, but they have a 28W TDP to take advantage of the extra GPU resources. ASUS has used some of the 28W ULV parts in the past so we may see these in a future ASUS offering.

As with Core i3, there are previous generation Core i5 parts that have a higher TDP and potentially higher performance, but these weren't used all that much (at least the 4th Generation Core i5 wasn't). The general thinking seems to have been that if dual-core ULV isn't sufficient for your processing needs, the better bet is quad-core processors. Which brings us to the final category of laptop processors.

Intel Core i7 CPUs

It would be great if Core i7 universally meant higher performance, but in today's mobile world that's not actually true. Core i7 means higher performance within the same classification, so an i7 ULV part is faster than an i5 ULV part, but a standard voltage Core i5 could still outperform a ULV Core i7.

Starting with the Broadwell side of things, as before only ULV parts are currently available, so there are Core i7-5500U and i7-5550U (the 5550U is being used pretty much exclusively by Apple right now it seems), which are basically faster variants of the i5-5200U/5250U, and then there's the "made for business" i7-5600U with vPro and TSX-NI support. There's also the i7-5557U, which as far as I'm aware isn't being used by anyone yet.

The problem with the ULV Core i7 parts is that all they really offer is a bit more performance than the Core i5 ULV parts. If you really want a lot of processing performance, however, you need a much higher TDP and hopefully more CPU cores to go along with it. We've had the Haswell Core i7 35W and 45W quad-core parts filling this role for nearly two years now, which means they're about due to be replaced... but the Broadwell parts haven't been released yet, and there's also Skylake waiting in the wings (due for a Q3 release by all accounts).

Until the Broadwell quad-core parts actually start shipping, your best bet is to either wait or just grab a Haswell quad-core. As with the Core i5 parts, the Core i7 quad-core CPUs all offer Hyper-Threading and Turbo Boost, the primary difference being that they now have two extra CPU cores. They also tend to have higher Turbo Boost clocks available, so at worst they should offer better performance than any of the dual-core parts, and at best they can more than double the performance thanks to the extra cores.

Considering the amount of performance offered, the Core i7-4720HQ starts at a rather impressive $700, and for CPU intensive tasks it should easily more than double the performance of any of the above Broadwell-U laptops. The expected Broadwell quad-core parts will likely be about the same level of performance, only with better power characteristics allowing for improved battery life, along with an improved GPU.

Wrapping Up -- Which CPU Is Right for You?

With all of the above discussion, some of you will inevitably wonder, "Okay, that's nice and all, but which CPU should I get?" The answer of course is a rather nebulous, "It depends." It depends on how much you're willing to spend, what you want to do with your laptop, and how much performance you want/need.

I'll be writing some actual guides in the near future, with the above overview of processors serving as an introduction of sorts. Because ultimately, the first and most difficult decision you'll have to face is what processor you want to use. For now, let it suffice to say that other than the slowest Intel and AMD processors (renamed Atom and AMD Mullins), all of the processors can fill a niche -- and even Atom/Beema can suffice for really light work, though they end up being more like a modern netbook than a real Windows laptop.

If you don't want to wait for the future laptop guides, from least expensive to most expensive my recommendations go something like this:
  1. Celeron 3205U is a great entry level part, but it's mostly in Chromebooks.
  2. Core i3-5005U doesn't cost much more and is faster.
  3. If you want graphics, AMD A10-7300 is a better solution.
  4. Core i5-5200U is next.
  5. If you need something faster, go for the Core i7-4720HQ or wait.
If you were hoping for more information related to the performance you can expect from the various processors, let me give you a rough estimate.
  1. AMD Beema or Intel Bay Trail: 100% (baseline -- yes, I consider these effectively "tied")
  2. Intel Celeron and Pentium U-series: 200-250%
  3. Intel Core i3-5005U: 300%
  4. Intel Core i5-5200U: 400%
  5. Intel Core i7-4720HQ: 600% (not twice as fast as i5-5200U because a lot of things don't scale with more than two cores)
Of course, choosing a laptop is more than just choosing a processor, so the guides will take a closer look at the various features along with the price points and processors to determine which are the best laptops currently available. Hopefully by the time I'm finished with the budget and mainstream offerings, we'll also have new quad-core Broadwell parts available. Stay tuned!

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