What is hypervisor?

A hypervisor is a special piece of software (or sometimes hardware) that lets one physical computer run multiple separate “virtual” computers at the same time. Each virtual computer, called a virtual machine (VM), thinks it has its own CPU, memory, storage and network, even though they’re all sharing the same real hardware.

Let's break it down

  • Physical host: The real computer with its CPU, RAM, disks, etc.
  • Hypervisor: The layer that sits on the host and creates/controls virtual machines.
  • Virtual machine (VM): An isolated environment that runs its own operating system and applications, just like a normal computer. There are two main types:
  • Type 1 (bare‑metal): Runs directly on the host’s hardware, no underlying OS. Example: VMware ESXi, Microsoft Hyper‑V, Xen.
  • Type 2 (hosted): Runs on top of an existing operating system like any other program. Example: VirtualBox, VMware Workstation.

Why does it matter?

Hypervisors let you do many things with a single piece of hardware that would otherwise need many separate computers. This saves money, reduces power and space usage, and makes it easier to test software, run different operating systems, or isolate risky workloads. It also enables cloud services, where providers offer VMs to customers on demand.

Where is it used?

  • Data centers and cloud platforms (AWS EC2, Azure VMs, Google Compute Engine)
  • Development and testing labs, where developers need to try software on different OS versions
  • Desktop virtualization, allowing a user to run Windows on a Mac, for example
  • Server consolidation, replacing many under‑utilized servers with a few powerful ones running many VMs
  • Security sandboxes, isolating potentially dangerous code

Good things about it

  • Cost efficiency: Fewer physical servers needed.
  • Flexibility: Spin up, pause, move, or delete VMs quickly.
  • Isolation: Problems in one VM usually don’t affect others.
  • Scalability: Add more VMs as demand grows without buying new hardware immediately.
  • Disaster recovery: VMs can be backed up and restored easily, even on different hardware.

Not-so-good things

  • Performance overhead: Virtualization adds a small layer of processing, so VMs may run slightly slower than bare metal, especially for heavy CPU or I/O tasks.
  • Complexity: Managing many VMs, licenses, and networking can become complicated.
  • Resource contention: If too many VMs compete for the same CPU, memory, or disk, performance degrades.
  • Security risks: A flaw in the hypervisor could expose all VMs; also, misconfiguration can lead to “VM escape” attacks.
  • Cost of licensing: Some enterprise hypervisors require expensive licenses or support contracts.