Qualification and validation of software and computer systems in laboratories - Part 4. Evaluation and validation of existing systems

Existing software and computer systems in laboratories require retrospective evaluation and validation if their initial validation was not formally documented. The key steps in this process are similar to those for the validation of new software and systems: user requirements and system specification, formal qualification, and procedures to ensure ongoing performance during routine operation. The main difference is that frequently qualification of an existing system is based primarily on reliable operation and proof of performance in the past rather than on qualification during development and installation.