When can have two possible meanings either “at the same time†or “afterâ€.
The continuous verb (-ing) = at the same time
When a program is being sorted, it is processed and stored.
While a program is being sorted, it is processed and stored.
The perfect verb (have +v –ed) = after
When a batch has been entered, it is processed by the computer.
After a batch has been entered, it is processed by the computer.
** Sometimes other forms of the verb are used and the meaning must then be gauged from the context.
When the data is entered, it is processed by the computer. = “while†(This would be ambiguous without the context.)
Replace “when†in the following with either “after†or “whileâ€:
1) When entering data, keep your eyes on the screen.
2) When the data is being entered, it is processed by the computer.
3) A new file is created when the data has been output.
4) Check the prices when shopping for a computer.
5) When a program has been output, it is backed up and saved.
