Asynchronous postback renders only the required part of the page; whereas, synchronous postback renders the entire page for any postback. Asynchronous postback executes only one postback at a time, that is, if you have two buttons doing asynchronous postback, the actions will be performed one by one; whereas, synchronous postback executes all the actions at once. Asynchronous postback only modifies the update panel that raises the postback; whereas, synchronous postback modifies the entire page.

Asynchronous postback renders only the required part of the page; whereas, synchronous postback renders the entire page for any postback. Asynchronous postback executes only one postback at a time, that is, if you have two buttons doing asynchronous postback, the actions will be performed one by one; whereas, synchronous postback executes all the actions at once. Asynchronous postback only modifies the update panel that raises the postback; whereas, synchronous postback modifies the entire page.

The difference are as follows : 1. Asynchronous post back renders only the required parts of the page, where as synchronous post back renders entire page. 2. Asynchronous post back executes only one action at a time. Whereas synchronous post back executes all action at a time. 3. Asynchronous postbox only modifies the update panel . where as synchronous post back modifies the entire page.