A legacy system is older software that still performs an important job, even as support, staffing, security, or future compatibility become harder to manage. Its age alone is not the reason to replace it: the system may be essential to a mature product and the customers who pay for it. section 1.4.1 section 8.0
Before planning a replacement, establish what is at stake:
- Find out which products and daily operations depend on the system, including dependencies that management may not recognize. section 1.2.3
- Identify who can keep it running and whether unsupported software or scarce expertise threatens that ability. section 1.2.3 section 1.4.1
- Assess running costs, security, scalability, and whether the system and its dependencies can continue to operate on available platforms. section 8.0
An application that works but cannot readily move
A Visual Basic application built in the mid-1990s may still support the business while relying on unsupported third-party libraries and an older Windows version. Its continued operation does not settle the question of how it will be maintained or moved to a newer platform. section 8.0
Treat modernization as a business-continuity decision, not a race toward newer technology. First identify what keeps the company running and shore up immediate weaknesses. Then investigate larger changes with a plan that avoids disrupting current customers and operations. section 1.4.1 section 1.2.3
