Digital Equipment Corporation (DEC) was purchased by Compaq Computers. Compaq was purchased by HP. In 2008, all I could find on HP's corporate site, was references to Compaq. Some of their pages reference DEC systems of the 1990's and later, which are or were supported "recently".
There are many Web sites devoted to DEC's minicomputers of the 60's and 70's and beyond including the PDP-11 line of minicomputers. They offer far more support and description than these Web pages. A Web search will find them.
Thanks to David Gesswein of pdp8online.com for permission to use these videos, which he produced. He created new videos and text descriptions in 2008, to support this exhibit and Web page. The PDP 8/I and ASR-33 Teletype are owned, maintained and described by him. These and other videos are on his Web site.
There is a Web archive site which links to other archive sites which have manuals on-line. The MANX Web site has its own database, to provide links to some of the on-line manuals for the PDP-11/20.
What do these boards do? Some Web sites with information about DEC boards of this sort are:
a field-guide list of DEC modules
by function is at this site
and the module list is also at this site
Schematics per board are at the pdp12.org Web site.