It is not recorded. The quantity of a product is calculated each time a new stock move has been generated. You will not find an absolute quantity in the database.

For the description behind this, please look at the documentation on Stock and Warehousing:

https://doc.openerp.com/book/5/5_14_Stock/5_14_Stock_illustration/

There is a postgres view called stock_report_prodlots, that has this information calculated by location. This is a decent method for getting stock values. I have used it for valuation reports. Calling the python methods for each product can be slow.

The stock as the other user mentioned is stored in the table stock_move. Each time a move occurs a new entry is created. It is a double entry system. A product is moved from one location and put in another.