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Intel's Core i5-8250U CPU reviewed

Kaby Lake Refresh rides in on Acer's Swift 3

The notebook PC is undoubtedly the meat and potatoes for PC makers these days, but the basic processing resources that laptops have offered for the better part of a decade have been just as stagnant as they have been on the desktop. Ever since Intel's Sandy Bridge microarchitecture made its debut, getting a thin-and-light Intel machine has meant getting a CPU with a TDP in the range of 15W. That chip has had two cores, as many as four threads, and a serviceable integrated graphics processor as the cherry on top.

Sure, power consumption has fallen as process sizes have shrunken, allowing for thinner and lighter laptops and longer battery life, among other benefits. But for folks who want more processing power from their mobile systems, period, it's been necessary to step up from thin-and-light machines to beefier systems with bigger batteries, thicker chassis, and above all, more pounds on the scale.

i7-8650U 1.9 GHz 4.2 GHz 4/8 8MB 2 Up to DDR4-2400
Intel UHD
Graphics 620
Up to 1150 MHz 15W
i7-8550U 1.8 GHz 4.0 GHz
i5-8350U 1.7 GHz 3.6 GHz 6MB Up to 1100 MHz
i5-8250U 1.6 GHz 3.4 GHz

2017 has been the hottest year for CPU performance increases in quite some time, though, so it's only fitting that Intel would finally shake things up with its first eighth-generation Core mobile processors, code-named Kaby Lake Refresh (or Kaby Lake-R). The first wave of those CPUs, announced back in August, encompassed two Core i5s and two Core i7s. Intel's latest 15W chips are quad-core parts with Hyper-Threading enabled, for a total of eight threads.

The Kaby Lake Refresh die. Source: Intel

Until now, four cores and eight threads in an Intel mobile CPU has been the exclusive domain of the company's H-series chips. Those parts generally carry 45W TDPs that require big honking cooling systems and thick chassis to operate at peak performance, and it's been rare to find one of those chips in a Windows machine outside of gaming laptops with dedicated graphics cards on board. (Apple's MacBook Pros are one notable exception.)

A block diagram of the Skylake client core. Source: Intel

The basic CPU core for Kaby Lake Refresh is the same Skylake microarchitecture we've known since 2015. Intel's 14-nm process has now gone through two cycles of improvement in that time, but Kaby Lake Refresh doesn't rely on 14-nm++ to deliver its extra cores. Instead, these chips are still fabricated on the good old 14-nm+ process that underpins Kaby Lake parts.

A typical Kaby Lake Refresh CPU package. Source: Intel

Although its continuing encores are a bit of a let-down for chip nerds, Skylake has aged remarkably well as CPUs go. AMD's Ryzen CPUs might not trail Skylake by that much on a clock-for-clock basis, but Intel can usually clock its chips much higher than AMD can. Skylake's pair of wider SIMD units gives it a further edge compared to the Zen architecture in some tasks, too.

Future generations of Ryzen CPUs may require Intel to dig more single-core performance out of its labs somehow, but for now, Skylake is still the best thing going in x86 CPUs. More of those cores in a given CPU is nothing to get disappointed about.

AMD's recently-announced family of Ryzen Mobile APUs poses another threat to Intel's performance crown, though: the potential of integrated Vega graphics processors. Intel hasn't changed the basic graphics architecture on board Skylake CPUs since 2015, either, so Kaby Lake Refresh uses what we might classify as Gen9.5 graphics execution units in a GT2 configuration. Gen9.5 made its debut with Kaby Lake, and it includes improved hardware support for encode and decode of 10-bit 4K HEVC content plus hardware decode support for 4K VP9 cat videos.

Ryzen Mobile APUs, on the other hand, boast much beefier IGPs with eight or 10 Radeon Vega compute units on board. It's hard to tell how those integrated graphics processors might stack up, since we don't have full specs for those parts just yet and their shared-memory architecture makes bandwidth calculations difficult. Still, the theoretical performance numbers we can tease out of AMD's specs for its Vega integrated graphics processors so far put Vega IGPs leagues ahead of an Intel GT2 IGP.

The hope for AMD, then, is that the combo of competitive per-core performance from Zen CPU cores and the potentially class-leading performance of Vega processor graphics is enough to sway buyers to its corner. The company already boasts three design wins with Ryzen Mobile chips, and those systems generally have appealing thin-and-light designs and reasonable spec sheets to go with their APUs.

Source: Nvidia

Intel's OEMs have a possible answer to Vega processor graphics, though, courtesy of Nvidia's GeForce MX150 graphics chip. Including this Pascal GPU in a system may not be as elegant as the all-in-one Ryzen APU, but the GeForce's 384 stream processors and 2GB of dedicated GDDR5 memory seem poised to deliver an experience similar to, if not better, than AMD's parts. The discrete graphics chip has some advantages, too, namely that it's not contending with the processor for memory bandwidth in one socket.

For entry-level gaming, the MX150 deserves to be taken seriously. At its 1532 MHz boost clock, the MX150 offers 1.18 TFLOPS of single-precision number-crunching performance, 23.5 Gpixels/sec of pixel fill rate, and 35.3 Gtexels/sec of texture-filtering capability. Those numbers more than make up for the shortcoming of the Intel GT2 IGP, and the MX150 does it in just 30W of board power. The performance-per-watt potency of the Pascal architecture cannot be denied. Of course, AMD's Ryzen APUs deliver the sum of their performance from a 15W TDP, but one should game on AC power for the best experience to begin with. The extra power draw of the MX150-and-i5-8250U combo isn't that much of a liability in that light.

The challenge for AMD's partners, then, is to deliver Ryzen Mobile systems at the right prices. The HP Envy X360 15z Touch, the first Ryzen Mobile system to go on sale, offers a Ryzen 5 2500U APU with Vega 8 processor graphics. That SoC pairs up with a 1TB mechanical hard drive, 8GB of dual-channel DDR4-2400 RAM, and a 15.6" IPS touch screen with Windows  and a convertible hinge. The whole package runs $749.99 at Best Buy right now, although HP's Black Friday deals have driven that starting price down to as little as $575 lately. Considering the ephemeral nature of those discounts, we'll use the $750 figure as a solid starting point.