Every CIO wishes to have modern IT infrastructure that is flexible, high-performant and scalable, robust and impenetrable for hackers, and of course easy-maintenance and cost-effective to operate. The Chief Digital Evangelists demand the greatest possible agility and adaptability in order to enable companies to adapt swiftly to dynamic markets and customer expectations.
The so-called legacy IT, i.e. the IT infrastructure setup several decades ago, was by no means designed for such requirements, the general conditions were completely different: Industrial production was designed for mass production, less for customized manufacturing (batch size: 0); high hardware and storage costs required a different software design than today. Note: In 1956, data storage for one megabyte of data was around 85,000 US dollars (adjusted for inflation at today's prices; nominal price in 1956: 9,200 US dollars). Today: 0.00002 US dollar.
In fact, the majority of IT systems today run on platforms that fall under legacy IT. This ranges from the Mainframe (e.g. IBM mainframe) to the much used Oracle Forms 6-11. One should, however, take a differentiated look. A general "We must do away with legacy IT" makes no sense, each legacy IT component has its own challenges, the criticality is by no means always alarming.
At the time of writing this glossary entry, I am working at Beta Systems Software AG, which among other things developes software applications for the IBM Mainframe, which is still in use in data centers of numerous financial institutions, retail companies or the Automotive industry. Actually, the majority of financial transactions (account transactions, credit card transactions, etc.) are still processed via the Mainframe. Only about 5 years ago, the Mainframe was labelled as a helplessly outdated - but the mood has changed: The Mainframe is more powerful for batch processing than any other system, the reliability is unmatched by other systems and the mainframe is extremely secure.
Of course, the Mainframe also has problems that are usually associated with Legacy-IT: Above all, there is a lack of specialists who are familiar with the Mainframe architecture and who can maintain legacy application software in Cobol or Assembler programming code. What we are now observing, however: The Mainframe ecosystem is being opened up to modern frameworks and programming languages; it remains to be seen whether this mainframe technology can thus re-establish itself as a modern platform that attracts significant new investment.
Conclusion: legacy-IT must undergo a check. In some cases a system may prove to be robust, the dynamics of change required may turn out to be very small, so that the system can be retained. In other cases there will be no way around a replacement, migration or upgrade.