Well, you wouldn't run the computer at a 1:1 resolution, it would be a logical lower resolution displayed at a higher resolution. For a 4K display, everything would show at the size it would be on a 2K display — but actually rendering at 4K, everything is much crisper rather than just blown-up pixels.

Apple calls it Retina Display, Windows calls it display scale. Apple made it mainstream in 2010 (iPhone) and 2012 (iPad, Macs) whilst Microsoft seems to have made it much more mainstream since Windows 8 and the introduction of its Surface computers.