Warm sites are backup facilities that are partially equipped and can be brought online relatively quickly in the event of a disaster. They typically have necessary infrastructure (e.g., power, networking) and some hardware but are missing the primary computer systems or up-to-date data.

Hot sites (A) are fully configured and ready for immediate use.

Cold sites (C) are empty facilities with just space and basic utilities.

Frequent sites (D) is not a recognized term.