[From "Origins and Development of TOPS-20" by Dan Murphy]

     Stanford wasn't the only other place where a PDP-10  architecture
machine  was  being  designed  and built.  The newly opened Xerox PARC
(Palo Alto Research Center) included a number of people from  BBN  and
other  sites  familiar  with  TENEX, and they were quite interested in
pursuing their work on that system.   Since  Xerox  was  then  in  the
computer  business,  PARC  couldn't  quite manage to just buy a PDP-10
from  DEC.   Consequently,  they  built   their   own.    It   was   a
single-processor  machine  compatible with the KA10 and BBN paging and
was designed and built in a relatively short time.  It ran TENEX for a
number of years.