Virtualization: Concepts, Hypervisors, and Platforms

Virtualization is a technology that lets one physical computer host multiple virtual machines (VMs) by abstracting the underlying hardware. In practice, a hypervisor (also called a virtual machine monitor) intercepts VM instructions and allocates CPU, memory, storage and network resources to each VMredhat.comredhat.com. This allows multiple operating systems to run concurrently on the same hardware, improving overall utilization and reducing costs. By sharing physical resources among isolated guest systems, virtualization can increase efficiency, flexibility, and scalabilityredhat.com. For example, a single server can be partitioned into many virtual servers, maximizing space, power, and maintenance efficiencyredhat.com. Virtual machines are sandboxed from one another, so problems in one VM (e.g. crashes or malware) do not affect others or the host, enhancing security and reliabilityredhat.com. In short, virtualization pools a host’s resources and presents them as independent virtual hardware to each guest OSredhat.comredhat.com.

Hypervisor Types: Type 1 vs. Type 2

There are two main hypervisor architectures: Type 1 (bare-metal) and Type 2 (hosted). A Type 1 hypervisor runs directly on the host’s hardware without a host OS, acting like a lightweight operating system to manage resourcesredhat.com. This bare-metal approach yields high performance because VMs have direct access to hardware and scheduling is done by the hypervisor itself. Type 1 hypervisors (for example, KVM, Xen, VMware ESXi, Microsoft Hyper-V) are common in data centers and enterprise servers. In contrast, a Type 2 hypervisor runs as software on a conventional operating system (e.g. Windows, Linux, macOS)redhat.com. The host OS handles hardware drivers and calls, and the hypervisor operates as an application layer above it. Type 2 hypervisors (such as Oracle VirtualBox, VMware Workstation/Fusion, QEMU) are easier to set up on desktops and workstations but incur extra overhead from the host OS.

Key differences include:

Open-Source Virtualization Platforms

Several robust open-source hypervisors are available, each with strengths and common use cases: