>I recently found an interesting manual:
>
>    EK-HS571-TM  HSC50/70 Hardware Technical Manual
>
>This gives quite a thorough coverage of the theory of operation of
>the HSC50/70 hardware.  It's marked something to the effect of that
>it's for DEC support personnel only, so I'm not sure how it escaped.

It probably escaped along with the DEC support personnel :-) Quite
a few of the ebay auctions for PDP-related manuals are for material
that is "Internal Use Only" (either stated up-front, or visible=20
in the accompanying images). Not too long ago, the VAXBI spec was=20
auctioned off.

>The HSC hardware is pretty amazing.=20

It certainly was interesting for its time. There's at least one
DEC Technical Journal article about the HSC (possibly an entire
issue - I'm not at home so I cannot check easily).

Antonio