The so-called "retina" Retina Display is just a screen definition level proposed by Apple, according to the algorithm given at the San Francisco press conference last March:
Where a represents the viewing angle of the human eye, h represents the pixel pitch, and d represents the distance between the naked eye and the screen. Here Apple has given two preconditions (it can be seen that Retina Display is really a very marketing "standard"...): The d in the formula has been set by Apple as a mobile phone 10 inches (approximately 25cm) in advance. The tablet is 15 inches (about 38cm) and the laptop is 20 inches (about 50cm); the a in the formula is also set by Apple as 1 arc minute, which is equal to the default "naked eye" vision level of 20/20 (and the domestic vision standard 5.0 is roughly equivalent). A screen that meets the above conditions can make a single physical pixel invisible to the naked eye. Such a screen can be called "Retina Display" by Apple.
According to the algorithm, it can be concluded that to achieve the so-called "retina" level screen, the screen pixel density of the mobile phone needs to reach 300ppi or more (note that the actual resolution of the P-array screen in the Samsung SA screen is smaller than the algorithm obtained); The pixel density of the screen needs to be more than 260ppi; the pixel density of the notebook's screen needs to be more than 200ppi.
Full HD screen refers to any size screen with a screen resolution of 1920X1080P or more.
It can be said that the resolution of mobile phones with full HD screens surpasses that of mobile phones with retina screens. A tablet with a full HD screen of about 7-10 inches is a tablet with a retina screen. A laptop with a full HD screen is not as clear as a laptop with a retina screen, and so on.