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Conclusion
The iPhone 6s and 6s Plus are not completely new phones, but they feel like it. Before we explain why, let's discuss the less significant changes starting with the design. Apart from a new Rose Gold color, the iPhone 6s looks the same as the iPhone 6. The stronger aluminum chassis are technically larger but not enough to notice, unlike the 6s Plus' extra weight, which gives it an extra hefty feel.
The displays are also unchanged, keeping the same size, resolution, and features. Performance parameters, including brightness, gamma, and contrast ratio are also similar to the previous generation, however, our test samples did show improved color accuracy.
Even the new 12MP iSight camera with deep trench isolation technology cannot hold back a sea of sameness. After taking pictures in a variety of conditions, it's difficult for us to see any appreciable difference in quality between the iPhone 6s and iPhone 6. Unfortunately, the iPhone 6s' heavy-handed noise reduction smooths away the very details its extra pixels are trying to capture. Using a more aggressive sharpening filter does slightly increase the perceived sharpness for parts of the image in focus. However, this extra sharpening can hurt the iPhone 6s in lower-light conditions where it tends to emphasize the noise grain. The 6s Plus avoids this problem by leveraging OIS to increase exposure time and reduce noise, a feature the smaller 6s still lacks. While the iSight camera in the iPhone 6s and 6s Plus is one of the best you can get in a smartphone, Samsung's Galaxy S6 remains the leader in photo quality.
Battery life is another metric where the new iPhone 6s models only achieve parity with their previous generation counterparts. The roughly 5 percent reduction in battery size and increase in processor frequencies are equally balanced by the move to a more efficient FinFET process and lower-power LPDDR4 memory. This, plus a smaller screen, is enough to give the iPhone 6s a small advantage over the Galaxy S6 in daily use. Getting through a whole day with either the 6s or S6 without recharging can be a bit of a stretch, though, depending on your usage patterns. The iPhone 6s Plus compares more favorably to its peers and lasts a full day even with extensive use.
One of iOS 9's new software features is Low Power Mode, which underclocks the CPU and turns off some background tasks to extend battery life. Android users have had similar low-power modes, either built into Android or added by an OEM, for some time now. With Apple's usual focus on battery life, it's a bit surprising it has taken the company this long to implement a similar feature. When running the CPU intensive Basemark OS II, we saw an impressive increase in battery life. There's no way to quantify the real-world gains since everyone uses their phone differently, but it's safe to say that this feature does work as advertised.
The similarities documented above seem to suggest an iPhone equivalence principle, where the experience of someone using an iPhone 6 while standing on Earth will be the same as someone else's experience using the new iPhone 6s in an accelerating non-inertial frame of reference. The math, however, does not support this: 1GB of RAM is not equal to 2GB. This single change is enough to make the iPhone 6s feel like a completely new phone. The frequent and frustrating app and webpage reloads that made an otherwise fast phone feel slow are gone. Multitasking on the iPhone 6s is fast and fluid, as is the whole UI; it is easier to move data between apps and much easier to get work done. Sometimes I even leave my laptop at home and just work on the 6s Plus.
Most tasks on the new iPhones feel faster because of Apple's Twister CPU, which has the fastest single-threaded performance of any mobile chip, and custom NVMe-based PCI-E storage solution. Pairing the two additional USCs in the PowerVR GT7600 GPU with higher bandwidth LPDDR4 memory nearly doubles graphics performance too. Excellent frame rates, a large catalog of games, Apple's Metal API, and almost no thermal throttling make the iPhone 6s a good choice for mobile gaming.
Unlike iOS 7's completely new user interface and iOS 8's application extensions, which allow apps to work together and share data, iOS 9's enhancements are more subtle. The most immediate difference is the improved stability (no more SpringBoard crashes!) and generally less buginess compared to iOS 8. Apple's default apps gain some new abilities too, including public transit directions in Maps, better attachment handling in Mail, and Notes grows beyond a simple text editor. There's also a new news aggregator app appropriately called News, and the iCloud Drive app makes iCloud behave a bit more like a true cloud storage service. iOS 9 also resolves the keyboard's caps lock mystery by switching the keys between lowercase and uppercase rather than relying on the nonsensical coloring of the caps lock key alone. Even better, pressing and holding anywhere on the keyboard turns it into a trackpad that allows for more accurate cursor placement and text selection (this works on both the iPhone 6s and 6s Plus). There are a number of other improvements that you can read about in this full iOS 9 review.
This brings us to 3D Touch, a new usability feature exclusive to the iPhone 6s and 6s Plus that adds another dimension, both figuratively and literally, to the standard multi-touch controls. Capacitive sensors integrated into the display's backlight measure the microscopic deflection of the cover glass when pressure is applied to the display. This data is combined with information from the touch sensor and accelerometer to adjust the sensitivity and to cancel out the influence of gravity. Haptic feedback is provided by Apple's Taptic Engine, which can reach peak output in only one cycle, providing a greater range of feedback events.
3D Touch enables several new actions. The one I consistently use and find the most useful is pressing on the left side of the screen to open the app switcher. This works well on the iPhone 6s, but it's a bit of a stretch for a right-handed user on the 6s Plus. It would be nice to have the option of choosing either the left or right side of the screen for this feature. After getting used to this method, double-clicking the Home button feels clunky and archaic.
In addition to pinch-to-zoom, we can now add Peek and Pop to our lexicon of touch-based gestures. Pressing lightly on the screen allows you to "Peek" at the underlying content, like pressing on a URL to see a preview of a webpage or pressing on an address to preview a map without leaving the current app. Pressing a bit harder will "Pop" it open full screen.
At the home screen, pressing lightly on an app icon opens a Quick Actions menu, similar to a right-click context menu, that provides access to common tasks. This feature is a bit hit or miss. First, not every app supports this feature. Second, it's not a big time saver. For example, the Quick Actions for the Camera app allow you to jump immediately into video recording mode, which is kind of useful, but the "Take Photo" option just opens the camera, requiring one extra step than just tapping the Camera icon like normal.
Ultimately, 3D Touch seems like a feature that smartphones should have always had rather than something revolutionary, like the computer mouse. It does contribute to a better overall user experience, though, and that's really what the iPhone 6s and 6s Plus are about. Yes, the A9 SoC is extremely fast, the camera and display are very good, and the rest of the hardware is not bad either, but what sets these new iPhones apart from other phones—and even prior iPhones—is that they are not frustrating to use. I do not find myself shaking my head at poorly implemented features or rolling my eyes when the phone overheats and throttles or cursing under my breath at spontaneous reboots. The iPhone 6s and 6s Plus pass two of my most critical tests: they run smooth and do not slow me down.
Apple iPhone 6s Plus
Apple iPhone 6s
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Matt Humrick is a Staff Editor at Tom's Hardware, covering Smartphones and Tablets. Follow him on Twitter.