history of multiplexed files

[A. Lester Buck]

In the book "Life with Unix", p42, a passing mention is made of design
mistakes in Unix:

	And yes, they made some design mistakes.  In fact, a lot of UNIX
	is the result of evolution.  Things that did not work out were
	removed (e.g., multiplexed files) or changed (e.g., file name
	lengths). [...]  The lack of mistakes in UNIX is as much due to
	divine understanding as it is to its chance to evolve without
	carrying around the baggage of those old mistakes.

What were "multiplexed files" and why were they a mistake?  Are there any
other things that were simply removed as mistakes in early versions of which
a recent student of Unix might not have heard?

[The only "multiplexed" objects in a version of Unix of which I know are
AIX/RT multiplexed devices, which generate a device name on the fly for
subdevices, such as virtual terminals.]

-- 
A. Lester Buck		...!texbell!moray!siswat!buck