Usage of which and that

yuji8

are there any rules that point out when to use \"which\" and when
\"that\"?
Example:
... concern all variables which/that are found in the computer program.
Is it correct to use either \"which\" or \"that\" ?
Can, in general, \"which\" be always interchanged with \"that\" and vice versa?
Thank you.

petersheng

... concern all variables that are found in the computer
program.