Enlarge / iOS 12 is the rare update that actually noticeably improves performance across a range of older devices. (credit: Andrew Cunningham)

When we tested iOS 11 on the iPhone 5S, it was clear that it was slower than iOS 10 had been but that the iPhone 5S’ hardware was fast enough to keep everything usable. That’s especially true if you tempered your expectations: the phone was going on four years old at the time.

But at the time, some of you asked us to test a handful of other older iOS devices, particularly the A7-equipped iPad Air and Mini 2 and the A8-equipped iPhone 6 Plus. In the iPads, the same A7 CPU and GPU that powers the iPhone 5S’ screen has to adequately support a tablet with more than three times as many pixels. And the A8 in the 6 Plus draws a 2208×1242 image which is then downscaled to the phone’s 1080p screen; that means using a CPU that was around 25 percent faster than the A7 and a GPU that was only 50 percent faster to support a phone with 277 percent as many pixels.

The upshot is that those devices can often feel sluggish or laggy compared to subsequent models. Later Apple chips—from the A8X in the iPad Air 2 and the A9 in the iPhone 6S and 6S Plus onward, approximately—remain more than fast enough to run iOS 11 without any huge degradation of performance. But with iOS 12 this year, we’re testing an iPad Mini 2 and iPhone 6 Plus in addition to the old 5S to get an idea of how well Apple was able to improve the responsiveness of these older devices, many of which are still in use as secondary phones and tablets or hand-me-downs (or by people who just see no particular reason to upgrade).