Screen resolution of a digital television, computer monitor, tablet, smartphone or display device is the number of distinct pixels in each dimension that can be displayed. Retina monitors sold by Apple are generally recognized as having a physical pixel density greater than 200 pixels per inch. This means that they have twice the pixel density of a classic resolution computer monitor. 4K monitors for PCs are reality and understanding pixel density has become important when choosing products along with screen size and display resolution. Pixel density is the specification that defines how detailed a display is. It is expressed in units of PPI (Pixels Per Inch).
4K is a not standardized description of a number of physical pixels. It’s an approximation of the number of pixels wide something is (as opposed to the previous convention of how many pixels tall as in 480p, 720p, 1080p, etc.). Something with somewhere around 4000 pixels wide will be called 4K. So you have a variety starting from 3840 pixels up to at least 5120 pixels on “ultrawide 4K” displays, broadcasts, or video.
4K is a high resolution with twice as many vertical and horizontal pixels as HD and refers to resolutions with a horizontal pixel count of about 4 million.
The only interface currently on the market for 4K displays that can display 4K 60 Hz is DisplayPort 1.2, which has a bandwidth of 21.6 Gbps. This is because a bandwidth of 16 Gbit/s is required to transmit 4K 60 Hz (3840 x 2160 pixels, 32-bit color, 60 Hz). This is significantly higher than the bandwidth supported by DisplayPort 1.1 (10.8 Gbit/s), HDMI 1.4a (10.2 Gbit/s) and DVI Dual Link (7.4 Gbit/s). For this reason, it should be noted that 4K displays connected via DVI-D or HDMI currently only work at 30 Hz.
