Diablo 630

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The Diablo 630 was a daisy wheel printer (computer printer) sold by the Diablo Data Systems division of the Xerox Corporation. The printer was capable of letter-quality printing; that is, its print quality was equivalent to the quality of an IBM Selectric typewriter or Selectric-based printer. The printer was capable of this quality at a nominal speed of 30 characters per second (roughly twice the speed of the Selectric).

Several technologies enabled this quality and speed:

The lightweight plastic daisy wheel was rotated by a closed-loop servo and could be positioned rapidly and accurately. Because the wheel could turn in either direction, the next character was never more than 180° away from the previous character (and related characters were grouped together so the average "seek" was much less than 180°).
Like the element on a Selectric the daisy wheel could be easily changed, allowing a wide variety of fonts and character pitches.
The printer used cartridge-loaded ribbons; both an economical endless cloth ribbon and a high-quality single-use film ribbon were available with colored ribbons provided by third parties. By contrast, Selectric-based printers could use only one type of ribbon—cloth or single-use carbon film—and were almost always equipped for the former for economic reasons.
The carriage was also servo-controlled and the printer could print with the carriage moving either forwards or backwards, saving most of the time that would otherwise be spent executing carriage-returns.
The servo control of the carriage permitted the use of proportional spaced fonts, wherein each character does not have to occupy the same amount of horizontal space.
Unlike Selectric-based printers, daisy wheel printers support the entire ASCII printing character set.
Paper motion was similarly servo-controlled allowing quick printing of subscripts and superscripts as well as fast slewing past white space.

Some versions of the Diablo 630 included a keyboard and strongly resembled a slightly overgrown Selectric typewriter, and in fact could be used as either an offline typewriter or as an interactive computer terminal. Unfortunately for a typist desiring to check the typed copy for errors, the daisy wheel mechanism hides the area just printed. Firmware in the machine would therefore make the carriage move quickly to the right of the typing position, revealing the most recently typed characters, after a few moments of inactivity. This was disconcerting to many users. Only a very slow typing speed would allow the wheel to get out of the way after every character; faster typing speeds resulted in the wheel continuously hiding the typed copy until the typist paused. This made checking the copy for errors a bit more awkward and slow than on Selectric-based terminals.

The same mechanism was also sold to OEMs. One notable user was Digital Equipment Corporation who resold the printer as the LQP01 (with a parallel interface) and the LQPSE (with an RS232 serial interface) and supported by Digital's WPS-8 word processing software.

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