Kernal-based virtual machine(KVM) is an open source virtualization technology build into linux kernal by default. KVM is a type 1 hypervisor which runs directly on underlying hardware rather than running on a host’s operating system. Other virtualization technologies such as virtualbox runs in host operating system which is not as efficient in sharing resources for guests as compared with KVM.
Any hypervisor needs some operating system-level components—such as a memory manager, process scheduler, input/output (I/O) stack, device drivers, security manager, a network stack, and more—to run VMs. KVM has all these components because it’s part of the Linux kernel. Every VM is implemented as a regular Linux process, scheduled by the standard Linux scheduler, with dedicated virtual hardware like a network card, graphics adapter, CPU(s), memory, and disks. Which decreases the overhead of managing everything by host operating system.