The pixel density figures are: 326ppi (pixels per inch) for smartphones, since they are expected to be held the closest to the face; 264ppi for tablets; and 220ppi for laptops.
Are there better screens than Retina displays?
Yes there are. At any rate, there are screens out there offering a higher pixel density in the various categories listed above. Most obviously, since the iPhone 6 launch, Apple itself offers an upgraded class of screens that it calls 'Retina HD'. But many Android devices surpass not only the Retina screens but even the Retina HD models. The LG G3, for instance, has a flabbergasting pixel density of 534ppi, which blows even the iPhone 6 Plus out of the water.
Of course, it's worth pointing out that, according to our previous definition of Retina, it's debatable whether increasing the resolution/pixel density beyond Retina levels really produces a 'better' display. After all, what's the point in making a screen sharper if the human eye is no longer noticing any difference?
(Some would argue that, in moving up to a higher pixel density with the iPhone 6 Plus - as we shall see shortly - Apple made a tacit acknowledgement that a higher pixel density can be perceived by the human eye. Another possibility is that Apple simply didn't want rival device makers boasting about their superior screens, that no one can really tell the difference between 401ppi and 534ppi, and that we are all pretending the emperor is wearing clothes.)
Okay, what about a Retina HD display? What the difference between Retina and Retina HD?
The term Retina HD display - so far - refers only to the screens on the iPhone 6 and iPhone 6 Plus, although it seems almost certain that the iPhone 6s or iPhone 7 will boast similar specs - and perhaps 2015 will be the year that Apple extends the Retina HD branding to the iPad line. The iPad Pro, for one, would benefit from the cachet and differentiation that Retina HD would offer, but the iPad Air 3 and iPad mini 3 are also possibilities.
But what is the definition of Retina HD? This appears to be a bit woolier than Retina.
Apple insists that both the iPhone 6 and the iPhone 6 Plus have Retina HD displays, even though they have different resolutions and different pixel densities from one another. The iPhone 6, indeed, has the same as the plain old Retina displays on the iPhone 5s et al, so we know that pixel density isn't the defining difference between Retina and Retina HD.
Retina HD display: iPhone 6
So what is the difference between Retina and Retina HD? Apple has been a little vague on this, but it appears to refer to resolution rather than pixel density, meaning that bigger (but not necessarily sharper) screens qualify.
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