When Exclusive Lock is on any process, no other lock can be placed on that row or table. Every other process has to wait till Exclusive Lock completes its tasks.

Update Lock is a type of Exclusive Lock, except that it can be placed on the row which already has Shared Lock on it. Update Lock reads the data of the row which has the Shared Lock as soon as the Update Lock is ready to change the data it converts itself to the Exclusive Lock.