How does Redis persist data on my local Apache server even after reboot and complete power down?

From how I understand, Redis uses in memory from which I gather my RAM if I am running a local apache development server. I tried powering down my computer and disconnected the power cable as well, but the redis data on my local server development website persisted when I powered back up my computer and tested my test website again. I thought RAM data gets completely wiped when I do a system reboot, how does Redis persist data even after reboot on my local development environment? Thanks! :)