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Screen Labeled Function Keys
A special case of [[Function Keys]] are keys which are placed in close proximity to screen labels. These are most commonly found in kiosk applications such as [[ATM]] [[Automated teller machine]]s and [[gas pump]]s. These were first developed by Hewlett Packard in the [[1970s]]. HP terminals first had two rows of 4 keys over which a paper overlay would be placed. Users of these terminals would, of course, lose these labels. Programmers found that the [[HP 2640]] terminals could lock the top two lines of the screen, so they displayed the key functions there. Starting with [[HP 2647]] terminal, the keys were re-arranged to correspond with 2 pairs of 4 labels at the bottom of the screen. These could be programmed by [[escape sequence]] or [[configuration screen]]. This would be further developed on the failed [[HP 300]] Amigo, which used keys at the right side of the screen and [[HP 250]] business computers which placed them at the bottom. By arranging functions in heirarchical trees, many functions can be implemented with only 8 keys.
Today, HP calculators use this arrangement to implement heirarchical trees of functions. They are rarely found on PC applications, even though the first IBM PC BASIC labeled function key use at the bottom of the screen, and there are 12 function keys, patterned after use on IBM terminals.
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