Suppose you have a form that has a tab control, say four tabs.  Each 
tabbed page has a subform in it.  Each subform has a different control 
source.  Even though one tab is visible at a time, you're opening one form 
with the four tab controls (including four subforms with four control 
sources) at the same time.

When the main form opens (unbound), does Access load all four of the 
subform's control sources into memory at once or does it only load the 
control source of the visible subform?  I want to get an idea of how much 
Access is taxing the computer's resources.