The Diablo 630 was a daisy wheel printer (computer printer) sold by the Diablo Data Systems division of the Xerox Corporation from 1980. The printer was capable of letter-quality printing; that is, its print quality was equivalent to the quality of an IBM Selectric typewriter, Selectric-based printer, or similar quality 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 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.
Some models supported wheels with two rows of characters, allowing for the machine to print in two different languages or with a large set of special symbols.
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 forward or backward, saving most of the time that would otherwise be spent executing carriage-returns.
The servo control of the carriage permitted the use of proportionally 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.
Bidirectional paper motion was similarly servo-controlled allowing quick printing of subscripts and superscripts as well as fast slewing past white space.
Servo control of both paper and carriage permitted the unit to be used for plotting, with resolution of 120×48 steps per inch. This was popular enough that special daisy wheels were made with a reinforced period (.), the character most often used for plotting.
The logic permitted simultaneous motion of the wheel, the carriage, and the paper. The hammer automatically struck only after all three motions completed. This minimized the time spent waiting for the motions to complete.
A related model, the Diablo 1620, included a keyboard and strongly resembled a slightly overgrown Selectric typewriter. In fact, a "local/remote" switch permitted it to be used as an offline typewriter as well as an interactive computer terminal. Unfortunately for a typist (in either role), the daisy wheel mechanism hides the area just printed. Firmware in the machine would make the carriage move quickly to the right of the typing position, revealing the most recently typed characters, after a few moments of inactivity. The result was still unsatisfactory 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 actual typewriters or on Selectric-based terminals.
The same mechanism was used in Xerox's 850 display typing system and 860PDS word processor, and 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.
The printer became so common, with so much software supporting its command language, that Diablo emulation became an expected feature on other daisy-wheel printers and even on early laser printers. This was so pervasive that at least one company lived by testing printers for full Diablo 630 compatibility.
