Here is the pictorial representation to show , how the dirty read occurs in the system. This is mainly occurs when we set the Isolation level from Read Committed to Read UnCommitted(NoLock). There is no difference between Nolock and Read UnCommitted in SQL Server.
Before reading this, you must have to read the previous one postUnderstand Concurrency : Pictorial Representation -Phase#1
Pictorial Representation of Concurrency | Read UnCommitted | Academy4Code.com