A hypervisor is one of those pieces of computing that quietly underpins a lot — virtual machines, cloud servers, and, indirectly, how some anti-cheats decide what they are running on.
What a hypervisor does
A hypervisor is software that lets one physical computer run multiple separate "virtual" computers at once. Each virtual machine believes it has its own processor, memory and devices; the hypervisor sits underneath, dividing the real hardware between them and keeping them isolated from each other. It is the layer that makes virtualisation possible.
The two types
Hypervisors come in two broad kinds. A type 1 hypervisor runs directly on the hardware, with no ordinary operating system beneath it — this is what powers data centres and cloud computing, where one physical server hosts many virtual ones. A type 2 hypervisor runs as an application inside a normal operating system — this is what most people use to run a VM on their own PC. The difference is what sits below the hypervisor: bare hardware, or a host OS.
Why anti-cheats care
Here is the connection to gaming. A modern processor can expose, through the CPUID instruction, a flag indicating that a hypervisor is present. On bare hardware that flag is normally clear; under virtualisation it is typically set. Anti-cheats read this. Because cheaters have used virtual machines to isolate cheat tools or evade hardware bans, the presence of a hypervisor is a signal an anti-cheat weighs — and some games refuse to run when one is detected.
The nuance
It is not quite that simple, which is worth knowing. Some hypervisor technology is now used by the operating system itself for security features, so a hypervisor being present does not always mean "a VM is running a cheat." Anti-cheats have to distinguish a security feature of the host OS from a full virtual machine, which is part of why hypervisor detection is more nuanced than a single yes-or-no flag.
The takeaway
A hypervisor is the layer that runs virtual machines, either directly on hardware or inside a host operating system. Its relevance to gaming is that processors advertise when one is present, and anti-cheats read that signal — which is why understanding the hypervisor explains how VM detection works underneath.