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Software and Hardware Reliability                                    1
Software Reliability DefinitionThe probability that the software will;  operate as required (i.e., without fail),  for a s...
Software Reliability - features• failures in software are design faults,• reliability during test changes continually  (ne...
Hardware Reliability - features• failure is usually due to physical deterioration• hardware reliability tends, more than s...
Fault, Error, Failure    (PERSON MAKES)                                                   ENVIRONMENT                     ...
Reliability MeasuresWhen we talk of reliability measures the irony isthat we invariably talk about failure measures.There ...
Ensuring Hardware ReliabilityHardware Reliability is ensured by conducting thefollowing tests:• Fault Tree Analysis• Failu...
Ensuring Software ReliabilitySoftware Reliability is ensured by following the following Techniques:• Defensive Programming...
• Error Detecting and Correcting Codes   To detect and correct errors in sensitive information.• Diverse Programming   Det...
Software Reliability Tests•   Software Quality Audit•   Software Rule Checking•   Unit Testing•   Software Integration Tes...
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Software and Hardware Reliability

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Software and Hardware Reliability

  1. 1. Software and Hardware Reliability 1
  2. 2. Software Reliability DefinitionThe probability that the software will; operate as required (i.e., without fail), for a specified time, in a specified environment. 2
  3. 3. Software Reliability - features• failures in software are design faults,• reliability during test changes continually (new problems are found as old ones are fixed / new code is never perfect)• phenomenon of software reliability growth• environment is important (platform/inputs) - new envt. may require s/w retest 3
  4. 4. Hardware Reliability - features• failure is usually due to physical deterioration• hardware reliability tends, more than software, towards a constant value,• hardware reliability usually follows the ‘bathtub’ principle,• again, environment is important; a proportion of hardware faults are design faults 4
  5. 5. Fault, Error, Failure (PERSON MAKES) ENVIRONMENT INPUT MISTAKES OPERATORCAN BE ATTRIBUTED TO POTENTIALLYONE OR MANY LEADS TO ZERO OR MANY OR FAULTS REVEALINGCAN BE ATTRIBUTED TO AND MECHANISMONE OR MANY LEADS TO ZERO OR MANY ERRORSCAN BE ATTRIBUTED TO LEADS TO ZERO OR MANYONE OR MANY FAILURE 5
  6. 6. Reliability MeasuresWhen we talk of reliability measures the irony isthat we invariably talk about failure measures.There are four general ways of measuringfailures against time; • time of failure, • interval between failures, • cumulative failures experienced up to a given time, • failures experienced in a time interval. 6
  7. 7. Ensuring Hardware ReliabilityHardware Reliability is ensured by conducting thefollowing tests:• Fault Tree Analysis• Failure Modes Effects and Criticality Analysis• Failsafe Tests• Fault Injection Tests• PCB Trace Anaysis and Circuit Simulation• Environmental Tests 7
  8. 8. Ensuring Software ReliabilitySoftware Reliability is ensured by following the following Techniques:• Defensive Programming To produce programs which detect anomalous control flow, data flow or data values during their execution and react to these in a redetermined and acceptable manner.• Fault Detection & Diagnosis To detect faults in a system, which might lead to a failure, thus providing the basisfor countermeasures in order to minimise the consequences of failures. 8
  9. 9. • Error Detecting and Correcting Codes To detect and correct errors in sensitive information.• Diverse Programming Detect and mask residual software design faults during execution of a program, in order to prevent Safety critical failures of the system, and to continue operation for high reliability.• Software Error Effect Analysis To identify software modules, their criticality; to propose means for detecting software errors and enhancing software robustness; to evaluate the amount of validation needed on the various software components. 9
  10. 10. Software Reliability Tests• Software Quality Audit• Software Rule Checking• Unit Testing• Software Integration Tests• Software/Hardware Integration Tests• Fault Injection Tests• System Validation 10

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