Revit uses background processes to carry out performance intensive tasks so you can continue working in the model.
Some processes in Revit run in the background so you can continue working and not have to wait for Revit to complete the current operation.
On the Status Bar, click Background Processes
to display a list of the processes running in the background. Currently, the following
Revit features operate as background processes:

- Color schemes
- Detailed Steel Modeling. See Detailed Steel Modeling Background Process.
- Volume calculations for piping systems
- Flow and pressure drop calculations for closed loop hydronic piping networks
- PDF Export (Optional setting)
- Mechanical systems analysis
Note: A warning icon displays for the Background Processes icon when Background Processes is disabled. See
Misc Settings in Revit.ini.