Unlike Android devices, Apple settled on specific screen size and resolution for iPhone and iPad which will need to be addressed when Apple moves both to larger screens. Ben Lovejoy:
There are two ways of increasing the size of a display. First, you can keep the resolution the same and simply use larger pixels. That’s what happens when a manufacturer makes a 1080P HD TV in both 40- and 50-inch sizes, for example. Both have 1920×1080 pixel displays, it’s just that the 50-inch display has larger pixels.
So, will a larger screened iPhone have larger pixels or more pixels?
If Apple stretched the current 4-inch display to 5 inches, while retaining the same 1136×640 resolution, the pixel density would decrease from 326ppi to 260ppi.
The other side of the coin:
Now let’s consider the alternative: increasing the number of pixels in direct proportion to the increase in screen size to retain the same 326ppi pixel density. For the sake of simplicity, let’s assume Apple keeps the aspect ratio the same. That would mean an increase in resolution from 1136×640 to 1420×800.
The problem here as that apps expect the iPhone to have a specific number of pixels, horizontal and vertical.
Just as when the resolution changed from the iPhone 4s to the iPhone 5, suddenly they have to support yet another resolution. All that work they had to do then, they now have to do all over again.
That won’t fly, so what’s another solution?
In iOS 6, Apple introduced the concept of Auto Layout. Instead of developers having to specify absolute pixel coordinates for objects, they are able to define a location in relative terms. For example, this object should be centred and at least 20 pixels away from neighbouring objects.
Not all developers adopted it. In fact, probably most haven’t, as there’s been no particular reason to so far. A change in resolution would provide that reason, and they’d then have apps that would play nicely with any future resolution changes.
In an age where competitors have greater resolution on their smartphones and tablets, I don’t think Apple will go backwards. Instead, I think we’ll see 4X Retina on a larger iPhone, and eventually on iPads and smaller iPhones. The trick to getting 4X Retina will be battery life and cost.