Which of the following hypervisors is physically installed on a server?

Type 1 hypervisors, also called bare-metal hypervisors, run directly on the server's physical hardware and manage hardware resources themselves without requiring a host OS layer underneath. Examples such as VMware ESXi and Microsoft Hyper-V (standalone) are deployed by installing them directly onto the server, giving them lower overhead and better performance than hosted alternatives.

Type 2 hypervisors are installed on top of an existing host operating system such as Windows or macOS, rather than directly on the physical hardware.

VDI (Virtual Desktop Infrastructure) is a desktop virtualization deployment model or architecture, not a classification describing how a hypervisor is installed on a server.

Hybrid is not a standard or recognized classification for how a hypervisor is physically installed on server hardware.