What is DFARS Compliance (NIST 800-171) and how does it compare to NIST 800-53?

NIST SP 800-171 and NIST SP 800-53, both provide a set of security requirements for protection of information and systems used by the government. The purpose and applicability of the security requirements depends on; 1)    the information to be protected (controlled unclassified information (CUI) vs. classified information) and 2)    the kind of system on which the information is processed, stored, or transmitted (Nonfederal information system vs. federal information system.