What is Legacy Software ?

Legacy software are older programs that are developed decades ago. The quality of legacy software is poor because it has inextensible design, convoluted code, poor and non-existent documentation, test cases and results that are not achieved.

Legacy software is software that has been around a long time and still fulfills a business need. It is mission critical and tied to a particular version of an operating system or hardware model (vendor lock-in) that has gone end-of-life. Generally the lifespan of the hardware is shorter than that of the software. As time goes on, the hardware gets harder to maintain but is kept because it is installed and (for now) working and has proven too complex and/or expensive to replace. Legacy systems include both the legacy software and the legacy hardware. Legacy systems are everywhere; banks, energy companies (including nuclear plants), manufacturing of all types (process control), the defense industry, transportation, hospitals, insurance, and more.

Most enterprises use legacy applications and systems that continue to serve critical business needs. Typically, the challenge is to keep the legacy application running, while converting it to newer, more efficient code that makes use of current technology and programming languages. While a business may require a legacy application for its activities, legacy applications create complications for the IT operations teams that support them. A legacy applications is frequently tied to a specific version of an OS or coding language. For example, an application that runs on Windows 7 may not be able to run on Windows 10, despite middleware or glue code added by a development team or the OS being backwards compatible.

Furthermore, the older an application gets, the more difficult it becomes for the company using it to acquire support services. When a vendor's development team no longer supports a third-party application, it can be difficult, or even impossible, for an operations team to keep the software running. Even small changes to a legacy system may result in slower performance, higher resource consumption and more frequent failures and crashes.

Obsolete systems cannot be maintained and utilized forever; at some point, an enterprise will upgrade hardware, coding language, OS or the application in question. Modernization and migration involve refactoring, repurposing or consolidating legacy software programming to realign with current business needs. The goal of a legacy application modernization project is to create new business value from existing applications. As time passes legacy systems evolve due to following reasons :
  • The software must be adapted to meet the needs of new computing environment or technology. 
  • The software must be enhanced to implement new business requirements.
  • The software must be extended to make it interoperable with more modern systems or database.
  • The software must be re-architected to make it viable within a network environment.



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