From Electronista:
"..We were a bit surprised to learn that Panasonic has taken an Ultra HD panel and packed it into a working Windows 8 tablet prototype, which looked much closer to a production device than many other prototype tablets we've seen. The 3840x2160 resolution equates to a density of 220 pixels per inch, essentially comparable to the iPad's Retina display but quadrupling the area.
"
http://www.electronista.com/articles/13/01/08/pixel.density.rivals.retina.ipad/
"..We were a bit surprised to learn that Panasonic has taken an Ultra HD panel and packed it into a working Windows 8 tablet prototype, which looked much closer to a production device than many other prototype tablets we've seen. The 3840x2160 resolution equates to a density of 220 pixels per inch, essentially comparable to the iPad's Retina display but quadrupling the area.
"
http://www.electronista.com/articles/13/01/08/pixel.density.rivals.retina.ipad/