Glossary · Automation fundamentals, platforms and components
Legacy system
Also known as: Legacy systems, Brownfield system
German: Legacy-Systeme
In IT and automation, a legacy system is an older system that is still in use but is based on outdated technology, is no longer or only partly supported by its manufacturer, or is hard to change and integrate.
- Automation components
- OT security
In one sentence
A legacy system is an older system still in use that relies on outdated, poorly supported technology and is hard to change or integrate.
Example
A 20-year-old controller still runs a press line; spare parts come from the second-hand market, and the program exists only on one laptop.
How it applies
- Engineering: Legacy systems are integrated via gateways or migrated step by step. Migration projects start with an inventory of hardware, software and undocumented functions.
- Security: Legacy systems often lack current security features and updates; Compensating controls such as segmentation are used.
- Documentation: Legacy systems frequently suffer from missing or outdated documentation. Recover what exists — programs, circuit diagrams, parameter lists — and document the as-is state before changes. Record known limitations and workarounds.
- Operation: Knowledge about legacy systems often rests with a few people; capturing it in documentation reduces dependency on them.
Legacy vs. obsolete
A legacy system may still be supported and reliable, only old. An obsolete component is no longer available or supported. Both call for lifecycle planning, but obsolescence adds urgency for spare parts.