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exoops is based on XOOPS 1.3.x. Its now a fork and has continued to develop. Whereas XOOPS utilised the smarty template system, exoops decided not to do this but rather refine the existing php code. To a large degree they have been successful in this.
One big difference between the current versions of Xoops, and earlier versions of XOOPS (like the 1.3 versions that exoops is based on) is that the developers made an exhaustive effort to reduce the number of SQL queries used to create a page.
To achieve this they used a template cache system (Smarty) that further improves performance since it caches the results of the php and MySQL when a page is made, and doesn't need to pull on the database each time a new user requests the same material.
Between the two items, it's a huge benefit to performance.
Happy Christmas to you and yours.