From mboxrd@z Thu Jan  1 00:00:00 1970
From: doug@cs.dartmouth.edu (Doug McIlroy)
Date: Sat, 08 Apr 2017 11:22:23 -0400
Subject: [TUHS] Unix clones
Message-ID: <201704081522.v38FMNjx017321@coolidge.cs.Dartmouth.EDU>

> That's interesting that that sort of thing dates back (at least) to the Labs.

Research couldn't hold a candle to Development on making smooth transitions.
You don't take a telephone switch offline to change a file format or the like.
The development cycle used to be about three years: one year for design,
one for implementation, and one to build a hybrid to bridge the transition.
At 2AM on Sunday, you'd install the hybrid on one of the dual cross-checked
 processors at a time, so the switch was never interrupted. Later you'd
dispense with the hybrid the same way.

Doug