There are two basic problems that could occur:

1. The record is read and the reading process makes changes to the record. While those changes are being made, the record is read by a second process, which will now retrieve out-of-date information, since the update has not yet been written back to disk.

2. A variation on the scenario above is that process 1 and process 2 read the same record. Process 1 makes changes - let's say to address. Process 2 also makes changes to the phone number. Process 1 saves the record first, and then process 2 saves it. The changes that were made to address by process 1 will be overwritten by the record written by process 2 (which will contain the original address).

The file manager should grant a request for simultaneous access only when both processes have read the record and will not perform update. When the record is read for update, most file managers will lock that record so other processes cannot access it until the update is complete. Such management usually also has timeout protection so a record cannot be locked for an indefinite time.