Legacy Code: Definition, Examples


Legacy code refers to an application system source code type that is no longer supported or updated. Usually, this code was used in older software or technology, but remains in the present infrastructure because it still operates as required despite its outdated nature. Its maintenance can be difficult owing to its age, outmoded programming languages, or lack of understanding by current developers.


The phonetics of the keyword “Legacy Code” is: ˈlɛɡəsi koʊd

Key Takeaways

Sure, here’s the information in HTML format:“`html

  1. Understanding is Key: Legacy code can often be complex and confusing due to the lack of documentation. Therefore, a significant amount of time and effort needs to be put in understanding the logic and structure of the code before making any changes.
  2. Maintenance Over Innovation: Working with legacy code often involves maintaining and updating older systems instead of creating new features. This can be due to the business relying on older technologies that can’t be quickly or easily replaced.
  3. Testing is Crucial: Legacy code often lacks testing. When creating updates or modifications, it’s particularly important to implement tests to ensure that changes haven’t broken any existing functionality.

“`Just copy this code and paste it into your HTML file. It will create a numbered list with three main points regarding working with Legacy Code.


Legacy code is important in the field of technology due to its widespread presence in numerous software systems and applications. It refers to an old or outdated codebase that is still being used within an application despite the existence of newer technologies and coding techniques. As the backbone of many critical systems like banking, healthcare, transportation and more, it is vital because updating or replacing it can be costly, risky, and time-consuming. Therefore, organizations must maintain and manage it effectively. Legacy code also represents accumulated business knowledge and understanding that new codes may not have. Despite the challenges it poses, understanding and working with legacy code is therefore inevitable and crucial in many tech-related professions.


Legacy code refers to the codebase of a software application or system that has been developed or updated over time by various programmers. This code is often written in an older programming language or uses earlier technologies, but it continues to be used either because it supports critical processes, or due to the cost or complexity of updating or replacing it. The purpose of legacy code is to maintain long-standing, operational systems, particularly in environments where stability, continuity, and performance are crucial, such as non-profits, governmental organizations, and corporations.Though legacy code often gets a bad rap for being outdated, its continued use in systems conveys its importance in the technology world. For example, many companies continue to rely on legacy code in their systems for core functionalities that are too essential to replace outright. Additionally, since rewriting or updating legacy code requires a significant investment of time and resources, these companies often opt to gradually update the legacy systems, making sure to not disrupt the necessary functions they serve. Therefore, understanding and managing legacy code is a crucial skill in software development and maintenance.


1. Banking Systems: Many of the world’s banking and financial institutions still run on legacy coding systems like COBOL. Developed in the 1950s and 60s, these systems are critical for daily operations despite being outdated in comparison to modern programming languages. The main reason for these systems still being used is the high cost and risk of migration to new systems.2. Air Traffic Control Systems: Air traffic control systems in many countries still rely on software written decades ago. These systems continue to operate because rewriting or replacing such deeply embedded and flight-critical software can introduce new, unforeseen risks. 3. Governmental Systems: Various government departments across the world also use legacy code. For instance, the U.S. Department of Defense still uses a 1970s-era computing system that requires eight-inch floppy disks to coordinate the operational functions of the nation’s nuclear forces. The system, known as the Strategic Automated Command and Control System, was written in Assembly language, which is considered a legacy code today.

Frequently Asked Questions(FAQ)

**Q1: What is legacy code?**A: Legacy code refers to an application system source code type that is no longer supported or which has been inherited from languages, platforms, and techniques earlier than current technology.**Q2: Is legacy code always bad?**A: No, legacy code is not always bad. It sometimes indicates that the software has been functioning well enough for a longer period. However, it may also represent outdated technologies which can cause various issues.**Q3: Why is dealing with legacy code often considered a challenge?**A: Dealing with legacy code is often challenging due to lack of understanding of the whole system, outdated documentation, the system’s complexity, and dependencies between components. **Q4: How can I effectively maintain legacy code?**A: Effective maintenance of legacy code can be achieved by documenting the system, implementing solid tests, regular refactoring where necessary, and slowly migrating to new technologies if possible.**Q5: What is the ‘legacy code dilemma’?**A: The ‘legacy code dilemma’ refers to the decision on whether to continue maintaining and updating a legacy system (which can be time consuming and costly) or to replace it with a new system (which can also be hugely time consuming, costly and risky in terms of data loss or system downtime).**Q6: Why is testing important in handling legacy code?**A: Testing is important in handling legacy code because it helps in understanding the system, catching bugs, and making sure that code changes do not break existing functionalities.**Q7: What is meant by ‘refactoring’ in the context of legacy code?**A: Refactoring in the context of legacy code refers to the process of changing the code to make it cleaner and more efficient, without altering its external behavior or functionality.**Q8: How does dealing with legacy code affect businesses?**A: Legacy code can affect businesses by causing slower response times to new market needs, higher costs for maintenance, and potential security risks if the system is based on unsupported technologies. **Q9: Can I automate the process of dealing with legacy code?**A: While some aspects such as testing can be partially automated, dealing with legacy code generally requires a detailed understanding of the system which often involves manual intervention.**Q10: Is it possible to prevent code from becoming ‘legacy’?**A: It’s impractical to completely prevent code from becoming legacy because technology and business needs continually evolve. However, following good coding practices and keeping the system up-to-date can minimize the likelihood.

Related Tech Terms

Sure, here is a list of five terms related to “Legacy Code” in HTML bulletpoint form:“`html

  • Source Code
  • Refactoring
  • Codebase
  • Documentation
  • Software Maintenance


Sources for More Information


About The Authors

The DevX Technology Glossary is reviewed by technology experts and writers from our community. Terms and definitions continue to go under updates to stay relevant and up-to-date. These experts help us maintain the almost 10,000+ technology terms on DevX. Our reviewers have a strong technical background in software development, engineering, and startup businesses. They are experts with real-world experience working in the tech industry and academia.

See our full expert review panel.

These experts include:


About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

More Technology Terms

Technology Glossary

Table of Contents