What is software reliability and its importance

What is Software Reliability ? and its importance

The subject of Reliability was first recognised during second word war. The primary steps taken were to establish joint Army and Navy parts standards and set up a vacuum tube development committee in June 1943. At the close of the war, between 1945 and 1950, several studies have been done.

High levels of reliability can be predicted and achieved as far as the hardware portions of modern large and complex real-time computer-based control systems are concerned but software is a critical part and plays a vital role in influencing the overall system reliability. Hardware reliability A statement of the ability of hardware to perform its functions for some period of time. It is usually expressed as MTBF (mean time between failures).

Software reliability tends to change continually during test periods. While hardware reliability may change during certain periods such as initial burn in or the end of useful life however it has a much greater tendency than software value.

From the beginning of the industrial age reliability problems have had to be considered. At first, reliability was confined to mechanical equipment. However, with the advent of electrification considerable efforts went into making the supply of electric power reliable. Reliability entered a new era with the onset of the electronic age, the age of jet aircraft flying at sonic, and supersonic speeds and the age of missiles and space vehicles.

Sometime soon, software reliability is going to become a highly visible and important field, unfortunately, given human nature, its thrust into prominence will only happen once we experience the software equivalent of the Chernobyl, Bhopal or space shuttle challenger disasters. Such a disaster is likely to happen in the next few years.

Software Reliability is important to attribute of software quality, together with functionality, usability, performance, serviceability, capability, installability, maintainability, and documentation. Software Reliability is hard to achieve because the complexity of software tends to be high.

Number of models have been established since the early 1970s, but how to quantify software reliability remains mostly unsolved.

There is no individual model that can be used in all situations. No model is complete or even representative.

Software Reliability is the probability that the program performs successfully, according to specification, for a given time period.

Most software models contain the following parts:

• Assumptions
• Factors

Differentiate between software reliability prediction models and software reliability estimation models

Basics	Prediction Models	Estimation Models
Data Reference	Uses historical information	Uses data from the current software development effort.
When used in development cycle	Usually made before development or test phases; can be used as early as concept phase.	Usually made later in the life cycle (after some data have been collected); not typically used in concept or development phases.
Time Frame	Predict reliability at some future time.	Estimate reliability at either present or some next time.

A reliability growth model is a numerical model of software reliability, which predicts how software reliability should improve over time as errors are discovered and repaired. These models help the manager in deciding how much efforts should be devoted to testing. The objective of the project manager is to test and debug the system until the required level of reliability is reached.