Most of the PC OEMs have refreshed their Skylake systems to include Intel's new Kaby Lake chips. Kaby Lake parts are for the most part drop-in replacements for Skylake parts—same chipsets, same power envelopes and cooling requirements—and some manufacturers have taken advantage of this fact. Dell's new XPS 13 is in most regards identical to the old XPS 13, for example, except for the processor swap. Some manufacturers have been a little more ambitious; HP's updated Spectre x360 adds Thunderbolt 3 and Windows Hello support as well as slashing the size and weight.

Microsoft, however, has gone for none of these routes. The Surface Pro 4 with its Skylake processor remains the current iteration of the company's productivity-oriented tablet and hasn't changed since its introduction. The Surface Book, the laptop that can do double duty as a tablet, also remains a Skylake system. But Microsoft has made an upgrade of sorts to the Surface Book range in the form of an even more expensive version that sits at the very top of the range: the Surface Book with Performance Base.

Specs at a glance: Microsoft Surface Book with Performance Base Base Best As reviewed Screen 3000×2000 13.5" (267 PPI), 10-point capacitive PixelSense touchscreen OS Windows 10 Pro CPU Intel 6th generation Core i7 RAM 8GB 16GB 16GB GPU Intel HD Graphics 520 + Nvidia GeForce GTX 965M 2GB SSD 256GB 1TB 1TB Networking 802.11ac/a/b/g/n with 2x2 MIMO antennas, Bluetooth 4.0 Ports Mini-DisplayPort, headphones, SD, 2 USB 3.0 Cameras Rear: 8MP autofocus, 1080p video

Front: 5MP, 1080p video, infrared facial recognition Size 12.30×9.14×0.59-0.90" (312×232×14.9-23 mm) Weight 3.68 lb (1.647 kg) Battery 18 Wh (tablet) + 62 Wh (base) Warranty 1 year Price $2,399 $3,299 $3,299 Sensors Ambient light sensor, accelerometer, gyroscope, magnetometer Charger 65W Other features Surface Pen, TPM 2.0

The Surface Book's big party trick is that the screen portion is the part that contains the computer; it has batteries, a processor, RAM, storage, and everything else. The keyboard base, the part that in a regular laptop houses the computer parts, contains only the keyboard, touchpad, and battery. On higher-end models the keyboard base also contains a discrete Nvidia GPU. This GPU is non-standard; it doesn't neatly line up with any of Nvidia's usual mobile parts, and while it's faster than the Intel integrated graphics, it's not as quick as the more mainstream numbered parts.

As might be guessed from the name, the Surface Book with Performance Base doesn't touch the tablet part of the system at all, and the original Surface Book review still holds true for basically every aspect of the system. It's the same old Skylake machine as it was since it was launched last year. The only part that changes is the keyboard base. On the outside, it's chunkier: it's a little bit thicker (by 0.08 inches/1.9mm) and a little bit heavier (by 0.34lbs/0.13kg), and the top surface bulges upwards. So much so that the keyboard, which stands proud on the normal base, is now recessed, though both keyboard and touchpad feel otherwise identical to the ones on the regular base.

That bulging thickness has been used to do two things. First, the battery is bigger: 61.2 Wh, compared to 52 Wh in the regular base for a total (between the tablet and the base) of 80 Wh, up from 70 Wh. Second, the GPU is upgraded: it's now a standard model, specifically, the GeForce GTX 965M.

This better GPU and bigger battery cost an extra $100 over the corresponding skinny discrete GPU version.











The consequences of this are obvious enough. For compute workloads and when using the integrated graphics, the Performance Base performs identically because nothing has changed. Graphical workloads, however, are substantially quicker: depending on the benchmark, we're seeing between 30- and 100-percent increases in performance in the switch to the 965M. It's definitely a faster chip, and if you want to use a Surface Book for gaming or other 3D intensive workloads, it's a clear improvement.

Microsoft has had to upgrade the cooling system in the Performance Base to cope with the 965M's greater power draw. During heavy workloads, the fan noise is definitely noticeable, though it seemed to cope adequately without throttling.





The longevity is nice too. The total battery capacity is about 14 percent bigger, and lo and behold, the runtime on battery is about 14 percent higher. It's a simple trade-off; the bigger battery weighs more and is thicker, but it lasts longer. If that's important to you, it's worth having.

Why isn't this a bigger upgrade?

The Performance Base does the job it's supposed to do; if you need more graphical performance or battery life from your Surface Book, it's clearly the option to go for, especially with a mere $100 price delta. But it nonetheless raises a number of questions.

The obvious one is, why hasn't Microsoft switched to Kaby Lake? A switch to Kaby Lake would likely provide a modest improvement in battery life, a modest increase in CPU performance, and a somewhat larger increase in integrated GPU performance. Even with the discrete GPU this is valuable, because many workloads (such as browsers) stick with the integrated graphics. Our understanding is that the Surface Book's tablet portion is up against the limits of Intel's thermal and power specifications, so much so that Kaby Lake wouldn't be a straightforward drop-in replacement. As such, making the upgrade may have required full revalidation and possibly a redesign of the cooling systems, which wasn't worth it for such a small update.

Problem is, the tablet (and the Surface Pro 4) would benefit from a refresh. Aside from their processors, the lack of USB Type-C or Thunderbolt 3 on these systems, while tolerable at their 2015 introduction, looks rather more intolerable as we head into 2017. These are still premium-priced systems, and they should offer premium features. Kaby Lake provides the impetus for just such a refresh.

Similarly, the choice of the older generation 965M, rather than the new 10x0 series, may have some people wondering why Microsoft hasn't gone for Nvidia's latest and greatest; I'd imagine that the project timeframes just didn't match up well. Nvidia's new chipsets are also more power hungry than the older ones, and with the dimensions of the Performance Base constrained by the need to remain compatible with the Surface Book, squeezing it all in might not have been possible.

The other annoying issue is that existing owners of Surface Books have no upgrade path. Microsoft isn't selling the Performance Base separately, so if you want one, you'll have to buy a whole new system. The performance gap is big enough that Surface Book owners running graphically intensive workloads would probably see significant gains from making the switch, but having to spend a minimum of $2,399 to get one is painful. There's nothing preventing swapping out bases—any Surface Book tablet can work with the no-GPU base, the old GPU base, or the Performance Base without problems—it's simply that Microsoft has elected not to sell them this way.

I've heard suggestions that there are fit and finish concerns with doing this—that tablets and bases are matched together in the factory to ensure that they still show good alignment and clean lines even in spite of the minute variations in manufacturing that inevitably occur—but I daresay most Surface Book owners would tolerate a small visual blemish if it meant they could make such an upgrade.

All in all, the Performance Base is a curiosity. Microsoft says that the Performance Base was driven by demands for more battery life and more graphical performance, and it certainly addresses those demands, but it feels like a bit of a stopgap. A proper Surface Book 2 is surely in development, and with a more complete redesign, it ought to be possible to get Kaby Lake and perhaps even a current generation GPU into the system. It's surprising that the desire for battery life and faster GPUs was apparently so immediate and so acute that Microsoft felt the need to get the new base out, and it suggests that perhaps Surface Book 2 is going to arrive later rather than sooner.

As such, it's hard to know whether to recommend the Surface Book with Performance Base or not. If it had been released in 2015 then yes, without a doubt, it'd be the premium pick for Surface Books. In late 2016, though, it's much harder to recommend a system with a previous generation processor and no next-generation connectivity. If a Surface Book 2 were imminent we'd suggest holding off and waiting for that, but the very existence of the Performance Base implies that a Surface Book 2 isn't imminent. If the Surface Book form factor is really the one you want—and it certainly has its appeal—and you don't want to wait, then this is the system to get. I just can't quite shake the nagging feeling of it being a lot of money to spend on a machine that's essentially a year old.

The Good

The GPU is faster.

The battery lasts longer.

The Bad

Fan noise under load.

No way to buy the base standalone.

The Ugly