[TUHS] Pipes (was Re: After 50 years, what has the Impact of Unix been?)

[Paul Winalski]

Regarding pipes and pipe-like interprocess communications facilities in
other operating systems, VMS has always had a pipe-like communications
pseudo-devices called mailboxes.  The main difference between Unix pipes
and VMS mailboxes is that pipes have distinct read-only and write-only file
descriptors.  Mailboxes do not--channels (VMS-speak for file descriptors)
assigned to a mailbox can be used for both reading and writing.  This means
that it is not possible to do "broken pipe"-type detection on a mailbox.
This very much restricts the usefulness of mailboxes.

I wrote a true pipe device driver for VMS as part of the DEC Shell product
(a port of the Unix Bourne shell to VMS).

-Paul W.
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