Ahypervisoris the software layer that enables virtualization—running multiple operating systems concurrently on the same physical hardware as separate, isolated virtual machines (VMs). Operating systems textbooks describe the hypervisor as managing and multiplexing core hardware resources such as CPU, memory, storage, and I/O devices among multiple guest operating systems. Each VM behaves as if it has its own hardware, while the hypervisor enforces isolation and schedules resource usage.

Hypervisors come in two broad categories.Type 1 (bare-metal)hypervisors run directly on the hardware (common in data centers), whileType 2 (hosted)hypervisors run as applications on top of a host OS (common on desktops). In both cases, the hypervisor is the key tool that makes “more than one OS at a time” possible.

System Restore is a recovery feature, not a virtualization platform. A partition manager can split a disk into multiple partitions, which can support dual-boot setups, but that runs only one OS at a time, not concurrently as VMs. A bootloader selects which OS to start at boot time; again, that is not simultaneous virtualization. Therefore, the correct tool that allows running multiple operating systems simultaneously as virtual machines is the hypervisor.