Other than performance, what is your major criticism of the approach
that Disco takes in constructing an operating environment for a
shared-memory multiprocessor?

The authors of Disco paper claim that making extensive changes to the
existing operating systems is difficult and time-consuming and that Disco
contains most of their features "at only a fraction of their complexity
and implementation cost". This strikes me because after reading the paper
I was under the impression that Disco is a very complex and
hard-to-implement and maintain system. The authors also claim that changes
to the existing operating systems can lead to instabilities and systems
can become unreliable. However, they seem to ignore the fact that the
developers who work on developing new software for shared memory
multiprocessors and who know their existing operating system very well,
have the freedom to basically start from scratch and design and implement
the system free from any existing weaknesses and designed specifically for
their goal. Disco seems to represent a set of patches to all the multiple
operating systems it works with. The good example of this is section 5 -
Experimental Results where the authors describe their ways to overcome
overheads by making multiple changes to the existing operating systems
used for their testing. The mode of this approach is reactive as opposed
to proactive mode of designing and implementing a single operating system.

Another question I was asking is how easy is it to introduce a new machine
with a new operating system into the existing Disco setup that already
contains a set of operating systems? This might lead to having to make
extensive changes to the existing Disco solution and who knows how much easier
it is going to be than designing stand-alone operating systems to run on
shared memory multiprocessors.

The next question is how is it applicable in the real world? Disco vendors
would have to rely on all operating system vendors. What if the operating
system vendor comes up with a patch release not compatible with Disco? What if
the new major release of the operating system goes out? In this situation the
conflict of interests is possible.