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6 Terminal Insanity Curses! Foiled Again! Unix is touted as an interactive system, which means that programs interact with the user rather than solely with the file system. The quality of the interaction depends on, among other things, the capabilities of the display and input hardware that the user has, and the ability of a program to use this hardware. Original Sin Unfortunately for us, Unix was designed in the days of teletypes. Teletypes support operations like printing a character, backspacing, and moving the paper up a line at a time. Since that time, two different input/output tech- nologies have been developed: the characterbased video display terminal (VDT), which output characters much faster than hardcopy terminals and, at the very least, place the cursor at arbitrary positions on the screen and the bit-mapped screen, where each separate pixel could be turned on or off (and in the case of color, each pixel could have its own color from a color map). As soon as more than one company started selling VDTs, software engi- neers faced an immediate problem: different manufacturers used different