A Monochrome monitor is a type of CRT computer monitor in which computer text and images are displayed in varying tones of only one color, as apposed to a color monitor that can Display text and images in multiple colors. They were very common in the early days of computing, from the 1960s through the 1980s, before color monitors became popular. They are still widely used in applications such as computerized cash register systems, owing to the age of many registers. Green screen was the common name for a Monochrome monitor using a green “P1” phosphor screen; the term is often misused to refer to any block mode Display terminal, regardless of color, e.g., IBM 3279, 3290.
An open Schneider MM12 from 1988. It uses a GoldStar Type 310KGLA amber tube.
Unlike color monitors, which Display text and graphics in multiple colors through the use of alternating-intensity red, green, and blue phosphors, Monochrome monitors have only one color of phosphor (mono means “one”, and chrome means “color”). All text and graphics are displayed in that color. Some monitors have the ability to vary the brightness of individual pixels, thereby creating the illusion of depth and color, exactly like a black-and-white television.
Typically, only a limited set of brightness levels was provided to save Display memory which was very expensive in the ’70s and ’80s. Either normal/bright or normal/dim (1 bit) per character as in the VT100 or black, dark gray, light gray, white (2bit) per pixel like the NeXT MegaPixel Display.
Monochrome monitors are commonly available in three colors: if the P1 phosphor is used, the screen is green monochrome. If the P3 phosphor is used, the screen is amber monochrome. If the P4 phosphor is used, the screen is white monochrome (known as “page white”); this is the same phosphor as used in early television sets. An amber screen was claimed to give improved ergonomics, specifically by reducing eye strain; this claim appears to have little scientific basis.
Well-known examples of early monochrome monitors are the VT100 from Digital Equipment Corporation, released in 1978, the Apple Monitor III in 1980, and the IBM 5151, which accompanied the IBM PC model 5150 upon its 1981 release.
The 5151 was designed to work with the PC’s Monochrome Display Adapter (MDA) text-only graphics card, but the third-party Hercules Graphics Card became a popular companion to the 5151 screen because of the Hercules’ comparatively high-resolution bitmapped 720×348 pixel monochrome graphics capability, much used for business presentation graphics generated from spreadsheets like Lotus 1-2-3. This was much higher resolution than the alternative IBM Color Graphics Adapter 320×200 pixel, or 640×200 pixel graphic standard. It could also run most programs written for the CGA card’s standard graphics modes. Monochrome monitors continued to be used, even after the introduction of higher resolution color IBM Enhanced Graphics Adapter and Video Graphics Array standards in the late 1980s, for dual-monitor applications.