Protection and security
• Protection is any mechanism for controlling the access of processes or
users to the resources defined by a computer system
• For example, a user whose authentication information is stolen (data could
be copied or deleted. It is the job of security to defend a system from
external and internal attacks
• Protection and security require the system to be able to distinguish among
all its users. Most operating system maintain a list of user names and
associated user identifiers (user IDs), and group indentifiers