Starting with version 4.00, the BOINC core client does time-slicing. This means that the core client may switch back and forth between results of different projects. This is done in a way that allocates CPU time according to the 'resource shares' you have assigned to each project.
For example, suppose you participate in SETI@home with resource share 100 and Predictor@home with resource share 200. A single-processor machine might be scheduled as follows:
1:00 - 2:00: SETI@home 2:00 - 3:00: Predictor@home 3:00 - 4:00: Predictor@home 4:00 - 5:00: SETI@home 5:00 - 6:00: Predictor@home 6:00 - 7:00: Predictor@home ...A two-processor machine might be scheduled as follows:
CPU 0 CPU 1
1:00 - 2:00: Predictor@home SETI@home
2:00 - 3:00: Predictor@home SETI@home
3:00 - 4:00: Predictor@home Predictor@home
4:00 - 5:00: Predictor@home SETI@home
5:00 - 6:00: Predictor@home SETI@home
6:00 - 7:00: Predictor@home Predictor@home
In every 3 hour period,
your computer spends 4 hours on Predictor@home
and 2 hours on SETI@home, which is the desired ratio.
This feature is necessary to handle projects like Climateprediction.net, whose work units take a long time (1 or 2 months) to complete on a typical computer. Without time-slicing, your computer would have to finish an entire work unit before it could start working on a different project.
When BOINC switches from one application to another, the first application is said to be preempted. BOINC can do preemption in two different ways; you can select this as part of your General Preferences.