Information Technology Reference
In-Depth Information
proved by increasing the MTTF or reducing the MTTR, and we will present
operating systems techniques that do each.
Throughout this topic, we will present various approaches to improving op-
erating system reliability and availability. In many cases, the abstractions may
seem at first glance overly rigid and formulaic. It is important to realize this
is done on purpose! Only precise abstractions provide a basis for constructing
reliable and available systems.
Exercises
8. Suppose you were tasked with designing and implementing an ultra-reliable
and ultra-available operating system. What techniques would you use?
What tests, if any, might be sucient to convince you of the system's
reliability, short of handing your operating system to millions of users to
serve as beta testers?
9. MTTR, and therefore availability, can be improved by reducing the time
to reboot a system after a failure. What techniques might you use to
speed up booting? Would your techniques always work after a failure?
1.2.2
Security
Two concepts closely related to reliability are security and privacy. Security -
is the property that the computer's operation cannot be compromised by a
Definition: Security
malicious attacker.
Privacy is a part of security | that data stored on the
Definition: Privacy
computer is only accessible to authorized users.
Alas, no useful computer is perfectly secure! Any complex piece of software
has bugs, and even otherwise innocuous bugs can be exploited by an attacker to
gain control of the system. Or the hardware of the computer might be tampered
with, to provide access to the attacker. Or the computer's administrator might
turn out to be untrustworthy, using their privileges to steal user data. Or the
software developer of the operating system might be untrustworthy, inserting a
backdoor for the attacker to gain access to the system.
Nevertheless, an operating system can, and should, be designed to minimize
its vulnerability to attack. For example, strong fault isolation can prevent third
party applications from taking over the system. Downloading and installing
a screen saver or other application should not provide a way for a malicious
attacker to surreptitiously install a computer virus on the system. A computer
Definition: computer virus
virus is a computer program that modifies an operating system or application
to provide the attacker, rather than the user, control over the system's resources
