Is it ensure, insure, or assure?
Uppercase-only text or display messages. Some archaic operating systems still emit these.
See also runes, smash case, fold case.
Decades ago, back in the days when it was the sole supplier of long-distance hardcopy transmittal devices, the Teletype Corporation was faced with a major design choice. To shorten code lengths and cut complexity in the printing mechanism, it had been decided that teletypes would use a monocase font, either ALL UPPER or all lower. The Question Of The Day was therefore, which one to choose. A study was conducted on readability under various conditions of bad ribbon, worn print hammers, etc. Lowercase won; it is less dense and has more distinctive letterforms, and is thus much easier to read both under ideal conditions and when the letters are mangled or partly obscured. The results were filtered up through management. The chairman of Teletype killed the proposal because it failed one incredibly important criterion:
"It would be impossible to spell the name of the Deity correctly."
In this way (or so, at least, hacker folklore has it) superstition triumphed over utility. Teletypes were the major input devices on most early computers, and terminal manufacturers looking for corners to cut naturally followed suit until well into the 1970s. Thus, that one bad call stuck us with Great Runes for thirty years.