How to find PID

Here in the TSQL Script to find PID Key:

USE master
GO
EXEC xp_regread 'HKEY_LOCAL_MACHINE','SOFTWARE\Microsoft\Microsoft
SQL Server\80\Registration','CD_KEY'
GO

References:

http://blog.sqlauthority.com/2007/02/28/sql-server-t-sql-script-to-find-the-cd-key-from-registry/

https://gallery.technet.microsoft.com/scriptcenter/Get-SQL-Server-Product-4b5bf4f8