Dover
Dovers were very early laser printers, likely the first ones produced in any numbers, designed at Xerox PARC. They were more robust successors to an earlier laser printer prototype built at PARC, the EARS. They could produce output on ordinary paper at about one sheet per second.
Dovers were driven by a special device controller the Orbit, composed of four cards in a dedicated Xerox Alto. A spooler, Spruce, which ran on the Alto, oversaw the printing, which was done by a subsidiary program, Sprint. Files in Press format (a predecessor to PostScript) were sent to the spooler over the Ethernet, using the PUP EFTP protocol.
Dover production started in 1976, when a small group of researchers at PARC, under John Ellenby, began buying used Xerox 7000 document photo-copiers and converting them to Dover printers. An early Dover was running in 1976, and many further ones were built, starting in 1977. PARC built three for their own use, and Electro Optical Systems in Pasadena made more (roughly 35 in total), for use elsewhere, in 1977-78.
Among the most important of those were several that were made part of the package of PARC equipment distributed to several prominent universities as part of a grant; MIT, Stanford and CMU each received one.
Conversion
Dovers were built out of cannibalized Xerox 7000 copiers; the existing document photo-copying optics were stripped out, and replaced with laser output units, the Raster Output Scanner (ROS). (The Electronic Image Processor (EIP) for the Dover is the interface between the Alto and the ROS.) The entire paper-handling path mechanical hardware of the 7000 was retained, un-changed. After conversion, the copying optics were turned back in to the copier division, for credit.
Components removed included:
- optical system
- control logic
- contact relay
- control console
- top cover
- top harness
Components retained, un-disturbed, included:
- paper feeder
- paper transports
- engines
- solenoid
- paper path sensing switches
Components added included:
- laser system
- engine control module
- solid state relay
- control console
- top cover
- top harness
- adapter modules
The added electronics are primarily contained on 5 cards plugged into a backplane:
- Command Adapter
- Video Adapter
- Motor Driver
- Engine Control
- Relay Board
All aspects of the operation of the new printing system were controlled by software in the Alto.
External links
- Programmer’s Guide to Orbit, the ROS Adapter, and the Dover Printer
- Dover documentation - a large package of Dover documentation, including material on the Dover, Spruce, Orbit, the 7000 copier, etc
- Laser Printers
- Dover Laser Printer
- Xerox Dover in MIT AI Lab - the caption is erroneous; the Dover was actually shared between the AI Lab and LCS; note also the Alto which drove it, under the table
