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Taking the Apple MacBook's Core M to its limits

By Kenny Yeo - 23 Jul 2015

Taking the Apple MacBook’s Core M to its limits

Investigating the Intel Core M processor

Late last year, Intel announced the launch of its fifth generation Broadwell processors, with the Core M processors being the first out of the stables. Broadwell represents the “tick” in Intel’s “Tick-Tock Model” and marks a shift to a smaller 14nm manufacturing process, allowing Intel to create even more power efficient processors based on the earlier Haswell architecture.

What’s remarkable about the Core M processors is that its has thermal power envelope of just 4.5W, low enough that it can be cooled passively. In other words, it doesn’t require a fan. As a result, using these processors, notebook manufacturers have been able to design devices that are thinner than ever.

If not for the Intel Core M, you won't see notebooks this thin and sexy.

A good example is the Lenovo Yoga 3 Pro which was one of the first Core M devices to hit the market. It measures just 12.8mm thick and weighs only 1.19kg. Core M processors were also designed to be used in 2-in-1 hybrid devices and the ASUS Transformer Book T300 Chi is an excellent example of such a device. The tablet display was only 7.6mm thick and only weighed around 700g.

And finally there’s the Apple MacBook, which takes the concept of an ultraportable notebook to the extreme. It’s 13.2mm thick and weighs just 920g. To achieve these impressive figures, Apple had to completely re-engineer numerous components such as the display and keyboard so that even though the MacBook is thin, it still retains Apple’s legendary reputation for solidly built notebooks. You can read up more about our impressions of this ultra thin and light Macbook in our review, but in this article, we're investigating the effects of using an Intel Core M powered notebook,


Performance Analysis

The Apple MacBook is powered by Intel’s Core M processor running at a slightly overclocked speed. Apple has clearly qualified their CPU batches to run faster and is extremely confident of their chassis design. Nevertheless, without a fan to provide active cooling, the processor can get toasty especially during sustained workloads. As we know, processors tend to throttle down clockspeeds as they get warm. If this happens, how does performance get affected? To find out, we decided to take the new MacBook and push it to its limits.

The MacBook's tiny logic board sits in the top middle portion of the chassis.

First, we would run Geekbench to find out how the MacBook performs when the processor is still "fresh" and cool. Then, we would push the MacBook to its limits by taxing the CPU for for an extended period of time. After which we would record the temperature just under the top portion of the bottom panel where the logic board of the MacBook sits, and run Geekbench to see how performance has been affected. Finally, we would measure the time taken for the MacBook to cool down and return to its original levels of performance.

Why measure the temperature of the chassis and not the CPU directly? This is because unlike more traditional CPUs, the Core M’s performance is dependent on skin temperature (surface temperature of the device) rather than actual CPU temperature. Pegging clock speeds to skin temperature will allow the CPU to remain in a boosted state for a longer period of time as the surface temperature of the device usually takes more time to increase to the point where it becomes too uncomfortable. This technique is similar to AMD’s STAPM (Skin Temperature Aware Power Management) as seen in their Mullins APU.

Here are our findings:


We used DOTA 2 to tax the MacBook as it stresses up the CPU and GPU. After about half an hour, it reached its warmest temperature of around 47 degrees Celsius, which is really toasty. Fortunately, the logic board sits in the upper portion and directly in the middle, so if you were to rest the edges of the MacBook on your lap, it’s not too warm to touch.

As our findings show, performance took a considerable nosedive as temperature increased. We are looking at drop of around 38% for single core performance and 31% for multi-core performance. Is it significant? Yes, of course, the figures tell us that performance fell by about a third. And this can be felt even in normal usage scenarios. Apps seem to launch a tad slower and some of the more intensive and interactive websites seem more sluggish to browse. Though this sounds grim, bear in mind that this is a worst case scenario and these figures were obtained after over 30 minutes of intensive workload - something that we doubt most owners would subject their MacBooks to.

Fortunately, thanks to all aluminum construction of the MacBook, temperatures returned to normal quite quickly. And within half an hour, temperatures of the bottom of the MacBook dipped back to the low 30s and its Geekbench performance was back to normal.


What does this all mean?

Though Core M processors have allowed notebook manufacturers to design slimmer notebooks than before, the fact that most of these devices have no active cooling means that a good chassis design is now more important than ever.

Even so, a good chassis design can only do so much as passive cooling has its limitations. As users, it is necessary to be aware of this and to align your expectations accordingly. That said, these devices were never built for heavy duty lifting in the first place and are more comfortable running everyday productivity tasks such as word processing, spreadsheets, web browsing and the occasional photo-editing and light video-editing. These workloads are nowhere near as intensive as running a game like DOTA 2, so performance is unlikely to be too adversely affected. For example, running Geeekbench over and over again saw performance dip by a maximum of around 10%, after which scores stayed consistent.

Notebooks won't be this thin if not for the Core M processors, but there are some compromises.

It's important to note that the temperature and performance issues affect not just the MacBook, but all Core M-powered devices. This why you might see reviews of Core M devices with performance figures all over the place. If you recall, in our review of the MacBook even though it has a lower-clocked Core M processor than the ASUS Transformer Book T300 Chi, it was still able to serve up higher frame rates in games. This goes to show that a well designed chassis can help make up for lower clock speeds. Likewise, an inadequate design can hamper performance.

These are still early days for the Intel Core M processor and the devices that we see thus far are really the first of a new wave of ultraportable notebooks and hybrid convertibles. Notebook manufacturers are no doubt still finding their way about and experimenting with designs and materials. And with advances made in other areas of technology, don’t be surprised to see even thinner and lighter notebooks in the very near future.

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