From VMS to UNIX

[guy at rlgvax.UUCP]

uses kernel and user mode
on the PDP-11) the FCS and RMS libraries have no extra privileges - they are
just user mode libraries - and the kernel I/O interface provides the abstraction
of a linear array of blocks (Stonebraker's article in CACM on OS support for
DBMSs to the contrary - the record-handling facilities of RSX are no more
in the kernel that any record-handling facilities in UNIX).  Of course, DEC
doesn't tell you how to do an OPEN or CLOSE QIO, and knowing them they may
even require executive-mode privilege to perform those or other operations
that RMS does.

Some of those DEC operating systems also let you install your own CLI
(the ten-dollar DEC word for what UNIX calls a "shell"), but I suspect it's
more complicated than installing a new UNIX shell, and they probably discourage
it in general and only think system programmers and system administrators
should do it...

One of the advantages to UNIX in this regard is that it doesn't try to keep
the keys to the kingdom away from everybody except Authorized users.  It gives
you enough rope to hang yourself, true, but it also gives you enough rope to
hitch your horse to your wagon...  It's "implementor-friendly" in that you
may have to devote energy to implementing things that the OS doesn't support
at all (like file and record locking), but it doesn't force you to do as much
programming around the OSs restrictions as other OSs do.

	Guy Harris
	{seismo,mcnc,we13,brl-bmd,allegra}!rlgvax!guy