When will *.ldf and*.mdf files be updated?

1. Whenwill*.ldf and*.mdf files be updated?
whenI open the archive folder , I can seemany ldf and mdf file.
WhenI arrangefile by modified and view the file as "detail". the latest update ldf and mdf file(example: date modify2010-8-4 ) will not changed unless I restart the wincc ,is it correct ? In my mind the date should be update timely.

[schnipp schnapp]

other two questions are splitted to following threads

Question about data recovery.

When shall we need to delete the data in the MMC card and for what kind of reason ?.

Thanks gent