Legacy System

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What is a Legacy System?

A legacy system is a computer platform, programming language, or software application that continues to be used to support critical business functions, even though there are newer alternatives.


In this context, the label “legacy” means that the technology has become so ingrained in an organization’s workflow processes and culture that replacing it would not be cost-effective at this time.

Why Are Legacy Systems Still in Use?

Simply put, if a legacy system is still reliable and does its job well, the direct and indirect costs of replacing a legacy system may just not be worth it.

Rip-and-replace and other modernization efforts can be costly in terms of both time and money. In fact, the change management challenges of replacing established systems that still work well can be so daunting that many organizations find themselves embracing the old adage, “If it’s not broke, don’t fix it.”

Risks of Using Legacy Systems

While initially, it might seem more cost-effective to stick with a paid-off system, the continued use of a legacy system can become too expensive in the long run.

Maintenance costs will inevitably rise as it becomes harder to find parts or expertise, and it will become increasingly challenging to implement new functionalities or get the legacy system to work with new business processes. That’s because legacy systems often operate in isolation and create data silos.

To make legacy systems ‘talk’ to newer technologies, organizations typically need to invest in custom interfaces or middleware. These solutions can be expensive, and they still might not offer optimal performance or reliability.

And finally, older systems typically do not receive security patches or software and firmware updates. This leaves them exposed to known vulnerabilities that malicious entities can exploit, which in turn can expose an organization to potential regulatory compliance, legal and financial repercussions.

Modernizing Legacy Systems

Modernizing legacy systems is not just a technical undertaking; it’s a strategic move that can redefine an organization’s agility, efficiency, and competitiveness in today’s market. By choosing the right strategy and aligning it with business needs, companies can breathe new life into their older systems and help ensure they still remain assets instead of liabilities.

Before diving into the modernization process for this type of digital transformation, however, it’s essential to assess the current state of a legacy system and get answers to the following questions:

  • What are the core functionalities of the system, and which functionalities are most critical for business operations?
  • Who uses the system, and for what purpose(s)?
  • What dependencies does the system have?
  • What’s the current cost of maintaining the system?

Once all stakeholders agree on the answers, it’s possible to craft a roadmap that is aligned with business goals and choose the best strategy for moving ahead.

One of the quickest ways to modernize a legacy system is to move it from an on-premises data center to a cloud environment. This strategy can offer immediate benefits such as scalability, better data resilience, and improved cybersecurity.

Legacy System Examples

Legacy platforms and applications often remain operational because they are deeply embedded in an organization’s business processes. Some examples include:

  • Windows XP: Despite Microsoft ending official support for Windows XP in 2014, there are still instances of businesses and industries using it, often because of application compatibility issues.
  • Older Database Systems: Some companies still rely on old versions of Oracle Database, Microsoft SQL Server, or IBM DB2 databases because migration to a new database management system (DBMS) could be costly and time-consuming.
  • Legacy Enterprise Resource Planning (ERP) Systems: Older versions of ERP systems like SAP R/3 or Oracle E-Business Suite can still be found running in some organizations.
  • Medical Systems: Devices like MRI machines, ultrasound machines, and other diagnostic equipment often run on older operating systems or software because of their long lifespan and high cost of replacement.
  • Industrial Control Systems: Many factories and utilities are still using Supervisory Control and Data Acquisition (SCADA) systems that are decades old.
  • Point of Sale Systems: Some smaller retail establishments still use older point-of-sale (POS) systems because they still work, and it’s not worth the cost to upgrade them.
  • Bank ATM Software: Some ATMs still run on Windows XP Embedded.
  • Older Office Software: Some businesses might still use older versions of Microsoft Office because they rely on macros and plugins that aren’t compatible with newer versions of the productivity suite.
  • Legacy Telecommunication Systems: Many businesses around the world still rely on older PBX systems for telephony instead of adopting newer VoIP services.
  • Aircraft Systems: Avionics and other in-flight systems sometimes run on legacy software and hardware because of long testing and certification cycles.

Legacy Programming Languages

Legacy programming languages are not as popular as they once were, but their use is so ingrained in certain systems and applications that it’s too complicated to replace them.

For example, many automated teller machines (ATMs) today interface with backend banking systems that still process transactions on mainframes running COBOL.

Completely phasing out COBOL has been a challenge due to the complexities and high costs of data migration and the dwindling number of COBOL programmers who would know how to transition these legacy systems to modern platforms.

Other legacy programming languages still in use today include:

  • FORTRAN (Formula Translation): FORTRAN continues to be used in scientific and engineering contexts, especially in high-performance computing.
  • Assembly languages: Assembly is still used in situations requiring low-level hardware access or optimization. It’s also taught in some computer science courses to give students an understanding of how computers work at a low level.
  • PL/I (Programming Language One): PL/I use over the years has declined significantly, but it may still be found in some legacy IBM systems.
  • RPG (Report Program Generator): RPG is still in use, especially within the IBM i platform (formerly AS/400).
  • ADA: While its popularity has waned in the general software development world, ADA remains in use in safety-critical and real-time systems, especially in aerospace and defense.
  • Prolog: Prolog remains in use for specific tasks in artificial intelligence (AI), expert systems, and other logic-based domains.
  • Lisp: Lisp and Scheme (a LISP dialect) are still used in research and some specialized areas, especially artificial intelligence.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.