Green screen refers to the use of a DumbTerminal to present data to the user, normally green text on a black background, with 25 rows of 80 characters using fixed width font. On some systems the 25th line was reserved for system status functions, limiting the application program to 24 lines. The width of 80 characters is a legacy of the HollerithPunchCard.  ''Not to mention the fact that monitors of that vintage generally lacked sufficient resolution to display many more characters.''

Monitors of that vintage were fancy light bulbs, it's the graphics cards that lacked resolution. There were 132-character wide displays. http://programmers.stackexchange.com/questions/148677/why-is-80-characters-the-standard-limit-for-code-width <- fun and enlightening

''"Fancy light bulbs"...???  Huh?  Actually, resolution limits are due to hardware limitations all the way from CPU and RAM speed, to physical characteristics of the CRT and stray capacitance and inductance of the monitor cable.  Maximum resolution is a factor of various things.''

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Green screen displays normally display a stable image, unlike scrolling TeleType displays.