The Kramer K424F 20-00008590 is a secure 4−port dual display DVI−D KVM combiner that allows secure, simultaneous work and interaction with up to four computers. It is an essential tool for heavy−duty users challenged by frequent switching between isolated networks. The K424F integrates up to four isolated sources at different security levels into two large displays. For enhanced security, a USB user authentication port (DPP) connects to a smart card or biometric reader. This requires the insertion of a physical authentication card or identification of a fingerprint to access the various computers/networks.