KVM :- KVM is a Kernel Based Virtual Machine is an open source virtualization Technology Built into Linux. KVM Converts let you turn Linux into Hypervisor that allow a Host Machine to run Multiple isolated virtual isolated Environments called Guest or vms. In KVM Ram is shareable but we can’t share Hard disk E.g ( if our Base Machine is having 100 GB Hard disk & we have Assigned 50 GB Hard disk to VM Total (100GB – 50 GB)= 50 GB . If we have Ram 8GB and we have Assigned 4GB Ram to VM and we can share the Resources of Ram. 

Hyper v :- Microsoft released Hyper-V in 2016 and it is considered a hot competitor to VMware’s Fusion and Oracle’s VM VirtualBox. Hyper-V is virtualization software that, well, virtualizes software. It can not only virtualize operating systems but also entire hardware components, such as hard drives and network switches. Unlike Fusion and Virtualbox, Hyper-V is not limited to the user’s device. You can use it for server virtualization, too. In Hyper V Hard disk is Shareable but Ram is fixed if suppose we have Hard disk having 100 GB We have Assigned 50 GB Hard disk to VM and VM is using only 25 GB Hard disk (25 GB + 50 GB)= 75 GB. 

Xen Server :- This platform is used by virtualization administratorsto deploy, host and manage VMs. It’s also used to distribute hardware resources — CPU, memory, networking, storage — to VMs. In Xen Server Both Hardisk & Ram is not shareable.