Update statement flow

I am not clear about the the redo logs, undo logs and in general what happens to an Update statement.

from what i have read when a data is modified the modified data is stored in the undo log. If it is not comitted then other users read the data from the undo log.
What happens when an update statement is never commited ? From i have read that uncommitted data will be saved to the data file.

 if the update is committed then it is updated in the datafile as well the redo log files. If it is in the arcchive mode as soon as the redolog file is full it is updated in thr archive file.

If the update is in a transaction the updated uncommitted data is stored in the roll back segments.

Plz help me by providing a detail flow of what actually happens including all the process involved. Received on Fri Jun 10 2005 - 06:33:54 CDT