Do OS's slow down with age? (was: DDJ article / UNIX vs BS/2)

[A. Lester Buck]

In article <12872 at steinmetz.ge.com>, davidsen at steinmetz.ge.com (William E. Davidsen Jr) writes:
> I talked to four system managers who handle both
> VMS and UNIX VAXen, and even those who really dislike UNIX as an
> interface agree that UNIX will run 20-30% more users on a VAX, at least
> when doing typical things like edit, compile, read mail, light
> computation, etc.
> [ ... ]
>   The reason is that VMS has a lot of overhead in starting a process,
> and a lot in file i/o, due to the many types of file. You have some
> features added in VMS (which may or may not be needed), but you pay for
> them.
> 
>   I will agree with you that it is possible to write an o/s for any
> given computer which will maximize performance, but it is not a given
> that performance is the goal of a proprietary o/s. In fact, given the
> low overhead of process startup and file i/o in UNIX, there is usually a
> limited place for improvement there. Using the fast file system (BSD and
> V.4) the overhead of directory access in UNIX is low.
> [ ... ]
>   The assumption that proprietary=faster is not universally true,
> although I agree that for any machine there is room to custom tailor the
> software to the hardware.

I was reading an article about VMS in the November 1988
issue of the tabloid "Computer Technology Review."
Titled "VAX managers cautioned on accepting VMS V.5" by
Clay Prestia, it mainly advises waiting for the bugs
to settle out for several months.  But at the end it
makes an astounding statement about VMS performance over
time (quoted without permission):
	   "As time passes, [bugs will be fixed].  The performance
	loss probable with V.5 is a problem that one can't
	currently expect to see resolved as time passes.  With
	the advent of V.5, the cumulative loss of productive
	capacity of VMS since V.3 now totals over 30% for many
	workloads.  CPU hardware may be getting cheaper measured
	on a per cycle basis, but the software induced productivity
	losses negate much of this savings.
	   Digital could restore much of the performance loss by
	supplying more than one variant of VMS.  As Digital
	supplies many disparate configurations of the VAX hardware
	platform, it ought to supply variants of the operating
	system software optimized to each of the different
	environments.  Just as Digital has been successful at
	making all VAX hardware configurations look the same
	to the user and applications, so could it succeed in
	doing the same with VMS variants."

Contrast this with the article "The Evolution of UNIX System
Performance" by J. Feder in the Unix volume of the AT&T Bell
Laboratories Technical Journal, October 1984.  The author
presents data showing improvements of approximately 30% in
various operating system performance measures in the time
span from 1979 to 1983, on several different architectures
(PDP-11/70, Vax-11/780 & /750, and 3B20S).

Ok, so why does Unix get better with age, across architectures,
while VMS gets worse with age, on a single architecture?

Maybe OS's have a youth, middle age, and decline.  In their
youth, an OS cleans up and tunes its fundamentals to improve
its performance.  Then a middle age spread starts in, with
no more performance gains, and maybe some loss because of
creaping featurism.  Finally, the load of backward compatibility
and support for new features that don't mesh well with
the original design lead to complete ossification and decline.

Was the 1984 Unix article a measure of the youthful Unix?
Is VMS creaking at the joints and well into its decline?
What do the above comments about tuning for VMS workload
mean, and does this have any relevance to Unix?  How much
have recent releases of Unix been at the expense of performance?
Will System VR4, with everything AND the kitchen sink, have built in
performance losses of a significant size?

-- 
A. Lester Buck		...!uhnix1!moray!siswat!buck