In order to gain access to the system a user is supplied with a user name together with a personal password.

The operating system will check the user name and password are valid before allowing the user to log in.

Some files may be open by anyone, others only by those users with a particular level of access. It is possible that some levels of access allow a user to read but not change the data. The main computer's operating system makes sure that file access is appropriate for the user's password.

It is a good idea to change a password regularly, and do not choose obvious ones like the name of a relative or your birthday. The most secure passwords will be long (8 characters or more) and involve a mixture of letters and numbers.