How does the textbox + button actually do the searching in asp.net?

I was just curious as to how the textbox + button search actually performs the search to fill up my gridviews, because I couldn't see anywhere that causes the databounds or anything. Is it a post-back thing? How does it work?! o.o

<asp:TextBox ID="SearchBox" runat="server"></asp:TextBox>
 <input id="Submit1" type="submit" value="Search" />
 

Thanks heaps :)

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