What difference between sharepoint web parts and User Controls？

UserControl:
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1.User Controls are like you are creating your own functionality though grouping up the asp.net controls.
2. Can not be used on any general Sharepoint page. You gotta code a custom page Layout  and embed the usercontrols.
3. Do not have the ability to communicate/connect to other User  controls on the same page.

 

WebPart:

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1.Web Part are the one that are personizable.

2. Can use on any page through out.
3. Webparts can communicate/connect to other webparts and make use of the master/detail.
4.Webparts are like usercontrols usercontrols are added in code but wedparts are added at runtime.

 

Do you have any ideas?/Or  yo can leave a message.(*^__^*)