If the instance crashes whilst there are uncommitted changes in the
datafiles then this is repaired during instance recovery during the rollback
phase after the roll forward of all the changes in the online redologs. This
is done by reading the redo logs to look for commits on all the rolled
forward changes. But in NOARCHIVELOG mode commits for any changes that were
in the datafile before the instance crash could have been recorded in the
redologs that have been overwritten. How does SMON know what has been
committed or not if the database is in NOARCHIVELOG mode?