change in run bars in 8?

[pc@ctt.ctt.bellcore.com (Peter Clitherow)]

Trivial question:  i note that on my nice xl400 under 8.0 (and 8.0.1)
sometimes *both* run bars disappear, when in run state.  now, the way i
recall things with 7.2 and prior, if you had started a computation, then
it was either running itself (run bar), waiting for disk (disk bar) or
waiting to be scheduled again, in which case another task was running
(once again, a run bar).

now in 8.0 at least on my imach, there are brief pauses for up to half a
second or so.  what is happening?  is this a new definition of "system"
time, creating new pages for instance, that shouldn't get a run bar
indicator?

just curious.
pc