[linux-audio-dev] What does it mean for jack to be "rolling" (newby)

[Jonathan Ryshpan]

I've been using jack and qjackctl with audacity under Linux (FC6).  It
seems to be working OK with 1 approx 1 msec xrun in a half hour
recording session, when unfortunately my backup system kicked in. 

However there's something I don't understand about jack, even after
reading a lot of the documentation.  At the bottom of the qjackctl
window is a set of arrows, like on an audio control device.  When I
click on the arrow pointing right, the green "Stopped" in the main
window changes to "Rolling".  What does this mean?  What are the other
arrows for?  No useful info on the web. 

The above recording session was done while jack was "Stopped".  Would
jack work better if it were "Rolling"?  

Please excuse these elementary questions.
 
Thanks - jon