Pixel Density – From Incompatibility to Super High Definition
Printdesigners may know the term “dots per inch”, whereas one dot is equal to 72 inch.
The early Macintosh chose 72 pixel per inch (ppi) so one pixel would approximately equal one point.
The problem of few pixels is the viewing distance of most displays. When reading a book or other piece of paper, the text is usually held at arms length distance.
Computer monitors tend to be farther away, somewhere around 1/3 the distance more than paper. So, for displays around 72ppi, Windows would indicate 96ppi.
On the positive side, it made text much more readable at equivalent point sizes on screen and paper. On the other side, it made Webdesign more complicated as en eleven point text on Windows matched eight point on the Macintosh.
The iPhone introduced itself with even 326 ppi. In order to prevent ultra small texts and elements or ultra-large font-sizes, everything will be scaled up to fit into the physical room of previous displays – the separation of physical and virtual pixel.