COMMIT/ROLLBACK process?

What happens when i COMMIT / ROLLBACK the work in DB2
Ex: A transaction process is updating say 100 records in to the table and committing the task. I want to understand this process, how these 100 records will get updated when a COMMIT is executed and until Commit where these records be read/stored?, in the buffer pages?

Please share your thoughts on Rollback process too.

Thanks.