What's the difference between a Located and Unlocated Variable in the Unity Pro software?

Issue
Difference between a Located and Unlocated Variable in Unity Pro

Product Line
Unity Pro

Environment
Unity Pro

Resolution
A Located Variable is a variable that is either mapped to an I/O Module or is associated to a Memory reference.
An Unlocated variable is a variable which is not mapped to the I/O or associated to a Memory reference (it is not possible to know its position in memory). A variable which has no address assigned is said to be unlocated.