Historic data may not have been converted into the new system format and may exist within the new system with the use of a customized schema crosswalk, or may exist only in a data warehouse. Backward compatibility (such as the ability of newer systems to handle legacy file formats and character encodings) is a goal that software developers often include in their work.Įven if it is no longer used, a legacy system may continue to impact the organization due to its historical role. In addition, the decision to keep an old system may be influenced by economic reasons such as return on investment challenges or vendor lock-in, the inherent challenges of change management, or a variety of other reasons other than functionality. It may simply be that the system still provides for the users' needs. While this term may indicate that some engineers may feel that a system is out of date, a legacy system can continue to be used for a variety of reasons. Legacy was often heard during a conversion process, for example, when moving data from the legacy system to a new database. ![]() By the 1980s it was commonly used to refer to existing computer systems to distinguish them from the design and implementation of new systems. The first use of the term legacy to describe computer systems probably occurred in the 1960s. Overview Although off-support since April 2014, Windows XP has endured continued use in fields such as ATM operating system software. 123 for Lotus 1-2-3, and text files encoded with legacy character encodings like EBCDIC. Examples in legacy software include legacy file formats like. An example would be a classic Macintosh application which will not run natively on macOS, but runs inside the Classic environment, or a Win16 application running on Windows XP using the Windows on Windows feature in XP.Īn example of legacy hardware are legacy ports like PS/2 and VGA ports, and CPUs with older, incompatible instruction sets (with e.g. While the term usually refers to source code, it can also apply to executable code that no longer runs on a later version of a system, or requires a compatibility layer to do so. Legacy code may be present to support legacy hardware, a separate legacy system, or a legacy customer using an old feature or software version. Long-lived code is susceptible to software rot, where changes to the runtime environment, or surrounding software or hardware may require maintenance or emulation of some kind to keep working. Legacy code may have zero or insufficient automated tests, making refactoring dangerous and likely to introduce bugs. Legacy code may be written in programming languages, use frameworks and external libraries, or use architecture and patterns that are no longer considered modern, increasing the mental burden and ramp-up time for software engineers who work on the codebase. Legacy code is old computer source code that is no longer supported on the standard hardware and environments, and is a codebase that is in some respect obsolete or supporting something obsolete. This can also imply that the system is out of date or in need of replacement. Often referencing a system as "legacy" means that it paved the way for the standards that would follow it. In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system", yet still in use. ![]() Old computing technology or system that remains in use In 2011, MS-DOS was still used in some enterprises to run legacy applications, such as this US Navy food service management system.
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