A long time ago I posed an interesting mystery to the folks on both the 
classiccmp and port-vax lists. That mystery was this, "What cable do I need 
to connect the KA660 in the BA400 cabinet to the DSSI bus?"

I asked the question because the KA660, like the KA640, has a DSSI 
interface on the CPU card. Further that interface comes out to a 50 pin IDC 
plug that is next to the 50 pin plug for the memory bus (just like the 
KA640). Further, in the right most slot of the BA400 series chassis with 
the Q/CD back plane is a board, M9715, that has a high density Honda 
connector and it plugs into the DSSI backplane. I reasoned that there was a 
DEC cable that went from the 50 pin IDC connector to the Honda connector 
and this provided the internal path to the DSSI bus.

I discovered later that the CD connectors on the far right of the Q/CD 
backplane in the BA440 are connected to the DSSI drives, and further that 
the KA660 routes the DSSI interface there so just plugging it in connected 
it to the DSSI backplane. And I never figured out what went in the M9715 
until now ...

DEC Part #17-02704-01 which is a replacement cover plate for the board, and 
has a DSSI connector on it and a cable that plugs into the Honda connector! 
This came off an B400X which had the Qbus extension in it and this 
cover/cable combination allows you to plug into the DSSI chain! Mystery solved!

--Chuck