At the heart of Apple's upcoming 12-inch MacBook is the Intel Core M, a processor series launched late last year and meant to power extremely light notebooks and tablets. But the new chips come with their own set of benefits and sacrifices, particularly for people considering other MacBook models.

At the moment there are seven models of Core M available, ranging in speed from 800 MHz to 1.2 GHz. All of them are dual-core, have a 4 MB cache, and are paired with the same integrated graphics chip, Intel's HD Graphics 5300.

Apple has chosen to go with the two fastest speeds — 1.1 and 1.2 GHz — for its stock configurations. The company is also promising a 1.3 GHz upgrade option, though no such chip is (yet) listed on Intel's website or even when browsing MacBooks at Apple's online store.

Pros: Smaller, quieter, more efficient

One of the leading traits of the Core M line is its standard 4.5 W of power consumption, a miniscule figure when you consider that other notebook processors can easily consume over 10 W. That effiency is attributable in large part to Intel using 14 nm architecture, claimed to be a first for processors.

It offers another advantage too, which is a smaller chip and die package. Indeed, the entire logic board for the new MacBook is about a third the size of the one in the MacBook Air, which is one way the computer manages to be so incredibly thin and light.

Less power also means less heat, allowing Core M machines to run fanless as long as they have proper ventilation channels. This contributes to the tiny dimensions of the MacBook, and should effectively eliminate noise.

Cons: Performance hits, no great battery leaps

There is one major drawback to Core M, and that's performance. Even the upcoming 1.3 GHz chip will still be clocked below the slowest current MacBook Air processor, which is a 1.6 GHz dual-core Core i5.

The two stock MacBook CPUs can Turbo Boost to 2.4 or 2.6 GHz, but the Air supercharges to at least 2.7 GHz. The Air can moreover be upgraded to a 2.2 GHz chip with a 3.2 GHz boost, and no matter which model you pick, you'll get an Intel HD Graphics 6000 chip for video.

Next to the MacBook Pro, the 12-inch MacBook doesn't even compete.

Next to the MacBook Pro, the 12-inch MacBook doesn't even compete. Entry-level Pro specifcations begin with a 2.7 GHz dual-core Core i5, paired with Intel's superior Iris Graphics 6100.

Since the new MacBook hasn't been released, it hasn't been benchmarked, but we can get a good approximation from another Core M system, the Lenovo Yoga 3 Pro. That notebook has a 1.1 GHz chip identical to Apple's, and according to Digital Trends has Geekbench scores of just 2,453 in single-core mode and 4,267 in multi-core. That slots it below the 2,565 and 5,042 of the cheapest 2015 Air.

For whatever reason, the Core M also fails to grant the MacBook any dramatic battery life advantage. Both it and the 11-inch Air are rated for nine hours of web browsing and 10 hours of iTunes movie playback. The 13-inch Air is even better, capable of 12 hours for each task.

The Retina factor

That may be attributable to the MacBook's signature feature, which is a 2304x1440, LED-backlit IPS Retina display. Although Apple hasn't shared many technical details, those kinds of specifications aren't easy on a computer's battery, as a rule. The advertised power consumption of the MacBook is actually 5 W, not 4.5, something that could be connected to video issues.

Indeed, imposing Retina-quality graphics on the Core M may create inherent speed problems, as the Yoga 3 Pro's benchmarks suggest. People buying a MacBook will likely have a tough time with Photoshop, much less high-end 3D gaming or video editing. It should be noted that the Yoga uses a 3200x1800 display, so the MacBook may not struggle as much.