Steven M. Bellovin said:

>Back in the mists of time (I mean *way* back), it was possible to mount 
>block tape devices as read-only file systems.  They did have very long 
>seek times, though, so this wasn't really recommended....  (There were 
>some DEC tape drives where it was possible to rewrite a block in the 
>middle of a file, and I think that those could be mounted read-write.)

Charles River Data Systems UNOS did this up until its demise a few years
ago. The OS was booted from tape for installation, and the tape was
mounted on /, read-only. Any tape containing a UNOS (aka V7) filesystem
could be mounted read-only. It was painfully slow.

I still have a Universe 68 system that will be attached to my network,
one of these days.
-- 
Rick Kelly  rmk@rmkhome.com  www.rmkhome.com