1. Computer Reliability
We are reaching the
stage where problems
that we must solve are
going to become
insolvable without
computers. I do not
fear computers;
I fear the lack of them.
Isaac Asimov

2. Are computers infallible?
From sophisticated
aerospace and military
digital systems to simple
word-processing and
spreadsheet applications
computer systems are
subject to hardware
malfunctions, software
bugs (or defects:
localized implementation
errors) or communication
failures.

3. Unreliable Hardware
The Therac-25 case is the
most striking incident of
unreliable machines.
Therac-25 was a
computerised radiation
therapy machine (used 1985
to 1987) caused six massive
overdose due to system
malfunctionherac-25
accidents are considered
the worst in the history of
medical accelerators.

4. Unreliable Software
The Y2K bug (or Year 2000
bug) is the best-known
example of software
unreliability. In order to save
computer disk space and
memory, computer
manufactures 60s to 80s
designed date fields only two
digits to represent a year four
(‘86’ for ‘1986’).In early 90s
computer programmers
realised that year 2000 be
interpreted by most software
applications as 1900.

5. What is computer reliability?
Computer reliability is
defined as the ability
of a computer system
to perform its required
functions for a given
period of time. It
includes the probability
that the system will not
fail during a given
period of time.

6. Hardware Reliability
Hardware reliability refers to the ability of
a computer system to perform without
errors. Hardware is unreliable when the
computer system presents unwanted
malfunctions or unpredictable breakdowns
in its mechanical components.

7. Software Reliability
Software reliability refers to the ability of a
computer system to deliver its usable services
when those services are demanded. An item
of computer software is unreliable when the
user’s expectations and demands are not
fulfilled by the program.

8. Data Reliability
Data reliability includes the following cases:
(1) data security: the protection of data (physical and digital)
must be kept confidential, safe, private and reliable;
(2) data privacy: the access of data only by authorized persons;
(3) data consistency: the correctness of data during processing
(input, process, and output);
(4) data integrity: the correctness of data both during and after
processing is related to the accuracy of digital data with
themselves and the correspondence of these data with the
real world. A computer system lacks integrity when digital
data do not correspond to the given information. Data may
have changed either by accident or due to malicious
purposes.

9. Principle of Discontinuity
Where analogue systems are infinite state or
continuous systems, digital systems are discrete
state or discontinuous systems. Digital computers
are discrete state devices with binary
representations and instructions, a computer
program may take so many different states that
they cannot be tested or predicted. In complex
systems, every change in the value of a variable
may cause millions of effects in the whole
system. All the possible states of the system
cannot be absolutely tested or predicted.

10. Professional Responsibility
Responsibility
involves all the
things for which an
individual is
considered to be
accountable.

11. Role Responsibility
Role Responsibility
refers to the duties of an
individual. Any role
(teacher, doctor, parent,
citizen) involves
responsibilities. Role
responsibilities are the
individual obligations to
behave in a proper
manner (in accordance
to the duties of the role).

12. Causal Responsibility
Causal Responsibility refers
to causality. According to
the causal principle, every
event has a cause so there
is a causal nexus (a link)
between a cause and its
effect. Causal responsibility
entails causal chain (a
sequence of factors leading
to a final effect) and it is
related to both human and
non-human factors.

13. Blameworthiness
Blameworthiness refers
again to causality but
of the individual
involved in the event. A
person may be the
cause of an event but
not blameworthy for the
situation.

14. Liability
Liability refers to the
accountability of an
individual for an action
or event. Liability
involves legal matters;
if a person is legally
liable for a situation
then this person is
responsible even if is
not blameworthy for the
situation.

15. Forms of Responsibility
There are two forms of responsibilities:
(1) responsibilities concerning the computer
professionals (computer systems may be unreliable
due to hardware malfunctions, software defects or
communication failures);
(2) responsibilities concerning the individuals use the
computer system consumers and end-users
(computer systems are unreliable due to the user’s
malpractice, misuse or negligence).

16. Possible Inadequacies
Following the stages of a system life
cycle as well as the ways that a
computer system is applied,
maintained and used the
inadequacies may occur at:
 System Analysis
 System Design
 System Development
 System Testing
 System Installation
 Mismanagement
 Lack of Service
 Malpractice
 Misuse
 Negligence

17. IT Solution
Computer professionals should provide fault-tolerant
computer systems capable of providing either fail-
safe or fail-soft protections. Fail-safe refers to the
full functionality of a computer system despite the
occurrence of a single fault, while fail-soft refers to
the reduced functionality of a system despite the
occurrence of a single fault. The latter is also
known as the state of graceful degradation: a
system continues to operate after a single fault
but a reduced level.

18. Liability Solution
The responsibility of a computer manufacturer has
to be by particular policies and standards (rules,
regulations and warranties). Any irresponsible
action against these standards must be
penalized. Supporters of strict liability maintain
that such penalties will encourage responsibility
of computer companies, enhance the quality of
software and hardware production and legally
protect the consumer from possible malfunctions.

19. Opponents
Opponents of strict liability argue that the
doctrine faces the following problems: applies
only to physical harm or property; does not apply
to services and complex systems that provide a
combination of goods and services; it focuses
only on the ultimate user. Strict liability
requirements will raise the cost of development,
testing and insurance. High costs will affect
small computer companies and will reduce
innovation and new software development.