Pixel

A pixel is the smallest resolvable rectangular area of an image, either on a screen or stored in memory. Each pixel in a monochrome image has its own brightness, from 0 for black to the maximum value for white (255 for an 8-bit pixel). In a color image, each pixel has its own brightness and color, usually represented as a combination of red, green, and blue intensities (RGB).

Pixel resolutions in Apple products
With the release of the original Macintosh 128K in 1984, Apple strove to achieve a minimum pixel density of 72 pixels per inch (PPI) to allow the implementation of WYSIWYG (what you see is what you get) for printing at 144 dpi. With the introduction of Retina displays, starting with the iPhone 4 in 2010, Apple strove to achieve a minimum density of 220 pixels per inch so that individual pixels were no longer discernable at normal viewing distances.


 * Apple II (1977) — 280 × 192 (hi-res mode)
 * Macintosh 128K (1984) — 512 × 342
 * Macintosh Portable (1989) — 640 x 400
 * MessagePad H1000 — (1993) — 240 x 336
 * iMac G3 (1998) — 1024 x 768
 * eMac (2002) — 1280 x 960
 * iPhone (1st generation) (2007) — 320 x 480
 * iPhone 4 (2010) — 640 × 960
 * iPhone X (2017) — 1125 x 2436
 * Pro Display XDR (2019) — 6016 x 3384