The monitor itself dictates whether it is capable of displaying a particular format--check the user manual. The number--1080, 720, 420--are the number of scan lines shown. The letter--p or i--says whether the signal is progressive (all scan lines drawn at once) or interlaced (half drawn and then the others filled in). Some videophiles believe 720p looks better than 1080i. Quicke, there is a third HD format that no one supports--1080p--which is supposed to be spectacular.
