The differences between 2K and 4K projectors

There are two kinds of 4K projectors : SXRD models manufactured by Sony are designed for 4K projection. DLP Cinema projectors made by Barco, Christie, NEC plus Kinoton and Cinemeccanica were originally designed for 2K projection; 4K models first appeared in 2009. Each of the three OEM manufacturers now develop 4K and 2K projectors, the latter remaining the most widespread throughout the world (about 2/3 of all digital cinema projectors sold at the end of 2012).

via The differences between 2K and 4K projectors.