Hypervisors and Virtual Machine Management | Generated by AI
A hypervisor (also called a virtual machine monitor or VMM) is the core software (or sometimes firmware/hardware) that creates, runs, and manages virtual machines (VMs) on a physical host computer. It is what makes virtualization possible by abstracting and sharing the physical hardware resources (CPU, memory, storage, network, etc.) among multiple isolated virtual machines.
Two Main Types of Hypervisors
| Type | Description | Runs Directly on Hardware? | Examples | Pros | Cons |
|---|---|---|---|---|---|
| Type 1 (Bare-metal) | Installed and runs directly on the physical hardware. No host OS underneath the hypervisor. | Yes | VMware ESXi, Microsoft Hyper-V (in hypervisor mode), Xen, KVM (when used bare-metal), Proxmox VE, Oracle VM Server | Best performance, higher security, lower overhead, used in production/data-center environments | Harder to manage for beginners, fewer built-in drivers/tools |
| Type 2 (Hosted) | Runs as an application on top of a conventional operating system (Windows, macOS, Linux). The host OS owns the hardware. | No (runs on host OS) | VMware Workstation, VMware Fusion, VirtualBox, Parallels Desktop, QEMU (when used with a host OS) | Easy to install and use, good for desktops/laptops, can use host OS drivers and tools | Slightly lower performance, more attack surface because of the host OS |
How a Hypervisor Works (Simplified)
- Resource abstraction – The hypervisor presents virtual CPUs (vCPUs), virtual RAM, virtual disks, virtual NICs, etc., to each VM.
- Isolation – Each VM is completely isolated; one VM crashing or being compromised normally doesn’t affect others.
- Scheduling – The hypervisor schedules which VM gets to use the physical CPU/RAM at any given moment (time-sharing).
- Trap-and-emulate – When a VM tries to execute privileged instructions (e.g., change page tables, access hardware), the CPU traps to the hypervisor, which safely emulates or handles the request.
- Hardware acceleration – Modern CPUs have virtualization extensions (Intel VT-x, AMD-V) that make the trap-and-emulate process extremely fast (near-native performance).
Common Use Cases
- Server consolidation (run dozens of VMs on one physical server)
- Cloud computing (AWS EC2, Azure VMs, GCP Compute Engine all use hypervisors under the hood)
- Development/testing environments
- Desktop virtualization (run Windows on macOS or multiple Linux distros side-by-side)
- Security sandboxes and malware analysis
Popular Hypervisors Today (2025)
- VMware ESXi – Dominant in enterprises (part of Broadcom now)
- Microsoft Hyper-V – Built into Windows Server and Windows 10/11 Pro
- KVM – Default in Linux, powers most OpenStack and public clouds (Google Cloud, AWS Nitro, etc.)
- Proxmox VE – Open-source Type-1 based on Debian + KVM + LXC
- Xen – Used by Oracle Cloud, AWS (older generations), XCP-ng
- VirtualBox – Free Type-2 from Oracle, very popular for personal use
- Nutanix AHV – Acropolis Hypervisor (based on KVM) for HCI
In short: the hypervisor is the “orchestra conductor” that lets multiple operating systems safely and efficiently share the same physical computer. Type 1 is what you’ll find in data centers and clouds; Type 2 is what desktop users typically install.