Retain variables preserve their values after a warm start. However, the degree of value retention for persistent variables is higher.

A special non-volatile memory area on the controller, for example as NVRAM or UPS, is required to extend the lifespan. Securing the retain variables in such a memory does not require any additional time, which is an advantage over data retention with the Persistence Manager. If the controller does not provide hardware support, then the data is usually stored in a file. Then the data will be retained if you shut down the controller correctly. In the event of a power failure or a "pulled plug", however, data will be lost.