Hello mac Bahi,
See attached image, it explains it a little better than I can.
This is taken from the DM1000 API specification, but I believe it works the same for the DM430E.
If you want even more information you can open the DM1x00 API from the hardware tab in PLUS+1 GUIDE (If you have the DM1x00 install that is), and search for "Main and Background Tasks". There are some very useful information.
I hope it helps.