Here is a very useful utility Windows 7 Product Key Checker which lets you to check and verify your Windows 7 Product key. Windows 7 Product Key Checker is an easy to use application designed to offer you a full description of the every fields of the product key, Product ID, Extended PID, Activation ID, Edition ID, License Type, License Channel, and Crypto ID.
Windows 7 Product Key Checker 1.0.1
The PID is the product id assigned to each oem manufacturer by edition (ie Home Premium, Ultimate, etc.). You can find the PID for a product key by using the online PID checker: Windows PIDchecker.