Preventive and perfective maintenance
Preventive maintenance refers to maintenance carried out to take account of anticipated changes in the processing environment. Changes in user operating procedures occur from time to time and software may require amendments to reflect this so as to prevent the system from failing or becoming obsolete.
Perfective maintenance is carried out in order to perfect the software or to improve software so that the processing inefficiencies are eliminated and performance is enhanced. It consists of making enhancements requested users to improve or extend the facilities available. For example, amendments to make software more user friendly.