Hypervisors

Hypervisor, also known as a virtual machine monitor (VMM), is a software layer that enables multiple operating systems to run concurrently on a single physical host by abstracting and managing hardware resources. It presents virtualized hardware to each virtual machine, including CPU, memory, storage, and network interfaces, while enforcing isolation between VMs.

Hypervisors are categorized into Type 1 and Type 2. Type 1, or bare-metal hypervisors, run directly on the host’s physical hardware and are common in data centers and cloud environments. Type 2, or hosted hypervisors, run on top of a host operating system and are typically used for desktop virtualization. Architecturally, a hypervisor schedules access to physical resources among VMs. It leverages hardware virtualization features provided by modern CPUs (such as Intel VT-x or AMD-V) to run guest operating systems with minimal modification and may provide para-virtualized drivers and I/O virtualization for efficient disk and network access.

Key capabilities include virtual machine lifecycle management (creation, pause, resume, snapshot, cloning), live migration of running VMs, resource isolation, and security controls between VMs. Performance depends on workload, hypervisor type, and hardware support, with Type 1 hypervisors typically offering lower overhead and higher density than Type 2.

Examples of well-known hypervisors include Type 1 products such as VMware ESXi, Microsoft Hyper-V, KVM, and Xen; and Type 2 products such as Oracle VM VirtualBox, VMware Workstation, and Parallels Desktop. Hypervisors are foundational to modern virtualization, server consolidation, disaster recovery, and cloud computing, enabling scalable, flexible, and isolated computing environments.