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In engineering, maintainability is the ease with which a product can be maintained in order to:
- isolate defects or their cause,
- correct defects or their cause,
- repair or replace faulty or worn-out components without having to replace still-working parts,
- prevent unexpected breakdowns,
- maximize a product's useful life,
- maximize efficiency, reliability, and safety,
- meet new requirements,
- make future maintenance easier, or
- cope with a changed environment.
In some cases, maintainability involves a system of continuous improvement - learning from the past in order to improve the ability to maintain systems, or improve reliability of systems based on maintenance experience.
In telecommunication and several other engineering fields, the term maintainability has the following meanings:
- A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed in accordance with prescribed procedures and resources.
- The ease with which maintenance of a functional unit can be performed in accordance with prescribed requirements.
Software engineering 
The measurement and track maintainability are intended to help reduce or reverse a system's tendency toward "code entropy" or degraded integrity, and to indicate when it becomes cheaper and/or less risky to rewrite the code than it is to change it.
See also 
- List of system quality attributes
- Maintenance, repair, and operations
- Supportability (disambiguation)
- Serviceability (disambiguation)
- Software Sizing
Further reading 
- Blanchard S. B., Maintainability: A Key to Effective Serviceability and Maintenance Management, John Wiley & Sons Inc., NewYork 1995
- Ebeling C. E., An Introduction to Reliability and Maintainability Engineering, McGraw-Hill Companies, Inc., Boston 1997.
- Patton J. D., Maintanability and Maintenance Management, Instrument Society of America, Research Triangle Park, North Carolina 19.