i found this:
Connectix says Apple apps get
preferential treatment in OS X. January
10, 2002 -- Yesterday we met with
Connectix executives to discuss the
cause of Virtual PC 5 slower performance
in Mac OS X, which we reported on
January 7. Connectix claims that some
Apple applications don't experience the
slowdowns of VPC because of extra
access to the processor given to Apple
applications. "There's a discrepancy
between Apple apps and non-Apple
apps." said Director of Product
Management Kurt Schmucker.
As we've previously mentioned, Connectix
says that VPC in OS X will never be as
fast as it is in OS 9. Connectix claims that
Virtual PC can't get enough processor
power in Mac OS X because of
preemptive multitasking. Virtual PC is not
"event driven" (using the processor in
response to user commands)--but
instead needs constant processing
power, which preemptive multitasking
can't give it, according to Connectix.
However, there are other nonevent driven
OS X applications that have good
performance--iTunes and iMovie, for
instance. Connectix claims that Apple
applications get access to the processor
that other apps don't. "It's undocumented
API's that give iTunes and iMovie their
smoothness," said Connectix QA
Manager Jeff Woolsey.
If they exist, these undocumented APIs
are the kind of secret trap doors that
Microsoft is often accused of using for
Windows applications. However,
Schmucker said he did not think Apple
was intentionally withholding technology,
saying that Apple already has given
Connectix help with porting VPC. "Virtual
PC exercises more parts of the kernel
than any other application," he said.
Schmucker also said that Apple is
currently working with Connectix to
improve VPC performance, possibly
incorporating changes in a future version
of OS X. We could not contact an Apple
representative for a comment.
Another issue for Virtual PC 5 is that it is a
Carbon application, which means it is
subjected to the processing overhead
that all Carbon applications are subjected
to. Carbon is the fastest way to port an
application to Mac OS X, enabling a
developer to retain large portions of its
code base instead of creating a new
application from scratch. (Microsoft Office
is also a Carbon application.)