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X was initially designed by John Socha for the original IBM PC. The purpose of X was to prevent phosphor burn-in on CRT and plasma computer monitors. The term X is named so because of this protection quality.
Identify X.

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Screensaver
Though most modern monitors are not susceptible to this issue (with the notable exception of OLED technology, which has individual pixels vulnerable to burnout), screensaver programs are still used for other purposes.
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