Legacy Systems
A legacy system, in the context of computing, refers to outdated computer systems, programming languages or application software that are used instead of available upgraded versions. Legacy systems also may be associated with terminology or processes that are no longer applicable to current contexts or content, thus creating confusion. In theory, it would be great to be able to have immediate access to use the most advanced technology. But in reality, most organizations have legacy systems - to some extent. A legacy system may be problematic, due to compatibility issues, obsoletion or lack of security support. A legacy system is also known as a legacy platform.[1]
Gartner defines legacy system as, "An information system that may be based on outdated technologies, but is critical to day-to-day operations. Replacing legacy applications and systems with systems based on new and different technologies is one of the information systems (IS) professional’s most significant challenges. As enterprises upgrade or change their technologies, they must ensure compatibility with old systems and data formats that are still in use."[2]
Challenges of Legacy Systems[3]
Legacy systems are considered to be potentially problematic by some software engineers for several reasons.
- If legacy software runs on only antiquated hardware, the cost of maintaining the system may eventually outweigh the cost of replacing both the software and hardware unless some form of emulation or backward compatibility allows the software to run on new hardware.
- These systems can be hard to maintain, improve, and expand because there is a general lack of understanding of the system; the staff who were experts on it have retired or forgotten what they knew about it, and staff who entered the field after it became "legacy" never learned about it in the first place. This can be worsened by lack or loss of documentation. Comair airline company fired its CEO in 2004 due to the failure of an antiquated legacy crew scheduling system that ran into a limitation not known to anyone in the company.
- Legacy systems may have vulnerabilities in older operating systems or applications due to lack of security patches being available or applied. There can also be production configurations that cause security problems. These issues can put the legacy system at risk of being compromised by attackers or knowledgeable insiders.
- Integration with newer systems may also be difficult because new software may use completely different technologies. Integration across technology is quite common in computing, but integration between newer technologies and substantially older ones is not common. There may simply not be sufficient demand for integration technology to be developed. Some of this "glue" code is occasionally developed by vendors and enthusiasts of particular legacy technologies.
- Budgetary constraints often lead corporations to not address the need of replacement or migration of a legacy system. However, companies often don't consider the increasing supportability costs (people, software and hardware, all mentioned above) and do not take into consideration the enormous loss of capability or business continuity if the legacy system were to fail. Once these considerations are well understood, then based on the proven ROI of a new, more secure, updated technology stack platform is not as costly as the alternative—and the budget is found.
- Due to the fact that most legacy programmers are entering retirement age and the number of young engineers replacing them is very small, there is an alarming shortage of available workforce. This in turn results in difficulty in maintaining legacy systems, as well as an increase in costs of procuring experienced programmers.