Hypervisor
A software, firmware, or hardware that creates and runs virtual machines.
A hypervisor, also known as a Virtual Machine Monitor (VMM), is a software, firmware, or hardware layer that creates and manages virtual machines (VMs). It abstracts the underlying physical hardware resources (CPU, memory, storage, network) and allocates them to multiple independent VMs. Hypervisors enable the execution of multiple operating systems and applications concurrently on a single physical machine, enhancing resource utilization, providing isolation, and facilitating portability. There are two primary types: Type 1 (bare-metal) hypervisors, which run directly on the host's hardware (e.g., VMware ESXi, Microsoft Hyper-V, KVM), and Type 2 (hosted) hypervisors, which run on top of a conventional operating system (e.g., VMware Workstation, Oracle VirtualBox). Type 1 hypervisors generally offer better performance and security due to direct hardware access, while Type 2 hypervisors are simpler to install and manage for desktop virtualization. Key functions include VM provisioning, scheduling, resource allocation, snapshotting, and migration. Trade-offs involve performance overhead, potential security vulnerabilities in the hypervisor layer itself, and the complexity of managing virtualized environments.
graph LR
Center["Hypervisor"]:::main
Rel_virtualization["virtualization"]:::related -.-> Center
click Rel_virtualization "/terms/virtualization"
Rel_virtual_machine["virtual-machine"]:::related -.-> Center
click Rel_virtual_machine "/terms/virtual-machine"
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🧠 Knowledge Check
🧒 Explain Like I'm 5
A hypervisor is like a teacher in a classroom full of students (virtual machines). The teacher has all the supplies (hardware) and decides which student gets a pencil or a piece of paper. The teacher makes sure no student bothers another student.
🤓 Expert Deep Dive
Hypervisors operate by intercepting and managing privileged instructions and hardware access requests from guest operating systems. Type 1 hypervisors achieve this through direct hardware control, often leveraging CPU virtualization extensions (Intel VT-x, AMD-V) for hardware-assisted virtualization. This allows guest OSes to run most instructions directly on the CPU, with the hypervisor intervening only for sensitive operations. Memory management involves techniques like shadow page tables or nested page tables to map guest physical addresses to host physical addresses. Type 2 hypervisors emulate hardware or rely on OS [kernel](/en/terms/os-kernel) modules for hardware access, introducing more overhead. Architectural trade-offs center on performance versus flexibility. Direct hardware access (Type 1) minimizes overhead but requires specific hardware support and can be complex. Emulation (Type 2) is more portable but slower. Security relies heavily on the isolation provided by the hypervisor; vulnerabilities in the hypervisor can compromise all hosted VMs.