SAM is more secure then normal Network. If Yes describe yourself.

SAM (Security Account Manager) on a  domain controller is more secure because it uses a database to hold the user accounts and passwords which is not availabe in workgroups (normal network). All the user accounts security principles are defined in SAM database and only authorized user can use the network resources.  

Yes it is way too more secure Atif. 

SAM is more secure as +Saqib Mehmood mentioned. For further details you can take at look at this link:

http://technet.microsoft.com/en-us/library/cc756748(v=ws.10).aspx