Massbus - was: Re: VAX 11/750

Oh this is fun stuff. Is there a specification write-up anywhere on the MASSBUS overall? For example I wonder if the RH70 could do a transfer >128kb at a time. Another is around the RH11: There were two models, the traditional RH11 (which could only do so many words on a DMA transfer) and the RH11-C which could do more words per transaction by basically running the Unibus in "Hog mode". That allowed the 2020 to run RM03's at a full 3600 RPM (and I assume can allow the 2020 to run things like RM80's). Another item I always wondered about was the RH11's support of two unibuses. I think the idea was to do the data transfers on the second bus right to an 11/45's FASTBUS memory without worrying about DMA timeouts while running the control and status registers on the normal UNIBUS (which wouldn't block other devices). I wonder, does the MBA on an 11/70 use similar cards to an RH11? C