[thrownaway2424]

Why do you really like that? 3840x2160 is exactly double 1920x1080, which is a useful property.

[Tepix]

I agree that it's useful for a TV but the 21.5" iMac is too small for that anyway - however if you want to edit 4k video, it's super useful to have extra pixels to be able to display a full UHD image with some GUI elements surrounding it.

[pazra]

They've used the DCI 4K resolution standard as the basis for their 4k screen, which is defined as 4096 x 2160 at 16:9 aspect ratio. This screen has a 16:10 aspect ratio, thus 4096/16*9 = 2304, the vertical resolution on the 4K iMac.

[thrownaway2424]

I'm afraid I didn't quite follow you there. Is one of those things using non-square pixels?

[dubya]

4096:2304 is still 16:9.

[Tepix]

I read it a couple of times, I think that's what he is saying why they chose that resolution.