What is SID in SQL SERVER 2008?

Question

What is SID? How this is interrelated with the user logins ? What is the functionality of the SID ? Can anybody explain it with simple words?

Answer 1

From Wikipedia's entry on Security Identifier:

In the context of the Microsoft Windows NT line of operating systems, a Security Identifier (commonly abbreviated SID) is a unique name (an alphanumeric character string) which is assigned by a Windows Domain controller during the log on process that is used to identify a subject, such as a user or a group of users in a network of NT/2000 systems.