Another goal will be to provide protection between applications, as
well as between the OS and applications. Because we wish to allow
many programs to run at the same time, we want to make sure that the
malicious or accidental bad behavior of one does not harm others; we
certainly don’t want an application to be able to harm the OS itself (as
that would affect all programs running on the system). Protection is at
the heart of one of the main principles underlying an operating system,
which is that of isolation; isolating processes from one another is the key
to protection and thus underlies much of what an OS must do.