TaskInstance

Where are the values stored in the Fields that belongs to a TaskInstance ? 

I mean if i declare in a workflow definition a variable A then i create a task (say Task1) and in it i create a field (say Field1) which is linked to that variable A.
When i run that workflow definition so to have the instance of Task1 where i find the value of Task1.Field1 ?

Thanks

Task fields are just user interface elements. The values are always read and written in workflow variables (in your example, variable A).