A Joomla website is composed of two parts:
- TheJoomla PHP code (files and folders on the disk);
- A DB where is stored all the data of the website.
With Multisite for joomla!, you can share the same PHP code (files and folders) that you connect to the data of multiple sites. Joomla multi sites is able to manage mutliples configuration files and therefore DB connections.

Creation of websites from the front-end is also a service that you can propose to your customers. Joomla Multi Sites contain all the elements to propose a such service.
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In Jms Multiple Sites version 1.1.x we have introduced the facility to replicate a website but was limited to a replication in the same DB than the website to replicate.
With multisite for joomla! version 1.2, it is now possible to duplicate website into another DB that can also be located on another server.
When you have all the MySQL root privileges, Joomla Multi Sites is also able to create DB dynamically as well as the DB user associated to the website.
This may be usefull when you propose the website creation from the front-end.
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