The User Interface (UI) is the access point to the Grid Infrastructure. This can be any machine where users have personal account and where their user certificate is installed. From the UI, the user can be authenticated and authorised to use the Grid resources and can access the functionalities offered by the Information, Workload and Data Management Systems.

The Worker Node (WN) is the computing node inside the Grid where the user's jobs are finally executed at a site. On the WN, the necessary middleware components are installed. Additional software components may be necessary according to the requirements of the site supported VOs.

Note: these days many VOs use UI and WN middleware provided through CVMFS, served either via their own repositories or via the generic grid.cern.ch repository.