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

[Paul De Bra]

In article <370 at siswat.UUCP> buck at siswat.UUCP (A. Lester Buck) writes:
> [long story reduced to key question: ]
>
>Ok, so why does Unix get better with age, across architectures,
>while VMS gets worse with age, on a single architecture?
>

The story for VMS is that it initially ran on Vaxen (780 mostly) with
little memory, and all updates/upgrades of VMS have been focusing on
optimization for speed versus memory. Added features slow things down
as always, but adding memory to the system and optimizing programs for
speed compensates. VMS supposedly still runs reasonably fast compared
to several versions ago, if you compare a machine with say 20 megabytes
to an old version of VMS on the same machine with only 4 megabytes of
memory.

The same more or less applies to Unix as well. There have been speed-
improvements, but mostly at the expense of using more memory. Unix has
had a benefit from introducing virtual memory, which was present in VMS
from the start. A major difference is that the Unix virtual memory does
well on heavily loaded systems compared to VMS, with its ridiculous
working-set system. Then Unix has had a breakthrough in disk-I/O with
the Berkeley fast file system, etc, etc. I think Unix has passed the
saturation point of vast improvements, and performance is going down
too, unless one adds memory. (remember the complaints from people who
supported 40 users on a 780 with BSD 4.1 and could only support 10
with BSD 4.2?)

Paul.
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