[Zak]

almost no one has sharp enough eyesight to distinguish individual pixels at even lower densities than that

That's exactly the point. Apple markets its high-PPI displays as being higher-resolution than the human retina[0]. It does need some help from software to not cause usability problems like font scaling and tiny images, but we've had the hardware capability to do this for a while. It's past time we improved on this.

Also, what's up with the 3:2 aspect ratio? That seems awfully odd.

If I had to guess, I bet a lot of the people involved in bringing this machine to market wanted 4:3, but someone in marketing and/or a focus group said that would be perceived as old-fashioned, so they got as close as they felt they could get away with. I'd really like to see a writeup on the reasoning from someone involved though.

[0] I believe the accuracy of said claim is disputed.

[Gormo]

> That's exactly the point. Apple markets its high-PPI displays as being higher-resolution than the human retina.

But the resolution doesn't need to be any higher than the maximum resolution of a human retina. By definition, you'd be unable to see the difference; you're just left with the scaling problems of an extremely high resolution on a very small display.

[Zak]

But the resolution doesn't need to be any higher than the maximum resolution of a human retina.

As I mentioned, the claim that the resolutions sold are higher than the human retina are disputed. See http://www.pcmag.com/article2/0,2817,2364871,00.asp

Apple's successive retina devices have decreased in pixels per inch, but have increased in pixels per degree at their intended viewing distance as larger high-PPI devices were introduced. Of course, sometimes people use devices at distances other than those the manufacturer intended, and some people have better eyes than others.

The point is, current high-PPI screens haven't actually banished the pixel from human perception just yet. There are still gains to be made, but they aren't nearly as significant as quadrupling pixel counts over previous devices.