The below mentioned steps will let you know how to find the underlying tables of a Info-provider and their details .
1. Go to tcode - RSRV.
2. Navigate to Tests In Transaction RSRV ->All Elementary Tests -> DataBase -> Database Information about InfoProviderTables . Double click on it . 
3. Double click on the "Database Information about InfoProvider Tables". In the pop-up window Enter the Infoprovider name .
4. Click on Transfer .
5. Drill Down To Database Information about InfoProvider0TCT_C01 tables -> Parameters -> <InfoProvider name>
6. Select the Infoprovider and click on 'Execute'. 
7. You will get a Log screen . Select the Database information about InfoProvider <InfoProvider name> tables .
a> It will give you the details of the underlying InfoProvider tables .
[How may entries are there in each of the tables and how much space they have consumed] 
8. You can further drill down more details about the table contents .