Technology Milestone: Desktop Performance in a Fanless Tablet with Core-M
Early PC designs did not demand a massive CPU cooling system to keep them happy. As engineers pushed performance with subsequent designs, an unfortunate side effect was the growth in waste heat. Heat sinks and attached fans had to be incorporated into system designs so that the CPU did not cook.
Heat was a problem for desktop designs as it introduced noise, the potential for failed fans, and required case designs to pump out waste heat with even more fans. The impact was far worse for laptops. Fitting a hot CPU needed a physically large chassis, slower, detuned CPUs to keep heat production as low as possible, and large batteries.
In 2003 Intel introduced its Centrino technology, and the era of more MHz at all costs ended. Thermal efficiency was on the radar and since that time focus in design moved to efficient multi core designs and technology which could allow the processor to throttle back and reduce its waste heat. Notebooks became increasingly viable as desktop replacements with new CPU designs allowing for thinner and lighter notebooks with better battery life.
The low power and low performance Atom processor introduced a new line of x86 CPUs for mobile in 2008, but did not possess the grunt to run many desktop applications. A recent update in 2013, the “baytrail” offered major performance improvements but is still only adequate for light use.
Each generation since the centrino has been another step toward a fanless, desktop level CPU. As mobile computing and tablets exploded, Intel redoubled their efforts to bring their performance processor design to the mobile market. The current generation “haswell” design is very close, take a look at products like the Surface 3, but still runs into thermal problems and requires a fan.
Enter Core-M, a critical tipping point for mobile computing
Intels next generation design, starting to roll out now, is “Broadwell”. CPUs based on this design share much in common with the previous “Haswell” processors, but have a substantive advantage related to their manufacturing process. Intel have physically shrunk the CPU by packing the components tightly with a 14nm process, a much delayed improvement over the 22nm process in current models. The practical result is that Broadwell bleeds less heat than ever before.
Multiple versions of Broadwell will be released from late 2014. The most exciting release is the Broadwell-Y range specifically targeted at tablets and ultrabooks. These processors are designed with 3.5-4.5W of thermal design power – the heat energy that needs to be dissipated during typical use. This is less than one tenth the heat generation of many desktop processors and sufficiently low that a light heat sink attached to a radiating surface such as the metal back of a tablet is sufficient to keep them cool. There are trade-offs against performance to bring heat production into this range, however they still retain the greatest part of their desktop CPU grunt.
Core-M performance – nibbles power like an Atom, with the grunt of an i5
Early benchmarks of 4.5W Core-M in shipping products suggest performance slightly slower than a 15W haswell i5 part, the most popular grunt CPU in current, high end ultrabooks. Performance is about 2-3x higher than the Atom/Baytrail processors currently dominating fanless x86 designs. Now we have hit the fanless mark, but only just, expect fanless performance to increase from two angles – incremental improvements in performance related design, and improvements in thermal efficiency so that CPUs do not need to throttle back as much.
Core-M is not a product where a few 10s of a percent variation against a full power chewing desktop processors matters.
What matters is Core-M can perform in a light and thin product with great battery life while pumping out ballpark desktop level performance.
What matters is that Core-M supports high performance desktop applications running on a product that might look like a current model ipad.
This release is a watershed moment in modern CPU design where a fanless CPU based on top end technology is again viable, and will now be standard for future generations.
Expect to see a wide range of Core-M products, many of which will not get the best from the CPU
In order to reach the fanless thermal efficiency, Core-M will throttle back aggressively under thermal stress and so reduce performance. When a spike of speed is needed, the chips can burst up in performance, but how well that burst can be sustained relates to how well the processor is cooled. For this reason, poor thermal designs will result in the chip running much slower than its potential, particularly under sustained high processing demands.
This also means that some benchmarks will not give it a fair run. Where real world activity may require short burst of high performance, benchmarks will usually hammer the CPU with continuous high load, causing Core-M designs to hit their thermal limits. That’s fair enough where applications might invoke similar conditions, but this is not the case for all high performance applications. Consider for example applying a filter in photoshop. The application might demand just a few seconds of full power, but will them throttle back when that work is down allowing the CPU to cool off.
It will be interesting to see how benchmarks vary by product using the same CPUs with Core-M releases – the variance will be a measure of thermal design effectiveness and may have a significant impact on real world performance.