Brodie, Leo. Under The Hood // Starting Forth. 2nd. Prentice-Hall, 1987. ISBN 0-13-843079-9. с. 241. To summarize, there are three kinds of variables: System variables contain values used by the entire Forth system. User variables contain values that are unique for each task, even though the definitions can be used by all tasks in the system. Regular variables can be accessible either system-wide or within a single task only, depending upon whether they are defined within OPERATOR or within a private task.
