QEMU是一套由Fabrice Bellard所编写的仿真处理器的自由软件。它与Bochs，PearPC近似，但其具有某些后两者所不具备的特性，如高速度及跨平台的特性。经由kqemu这个开源的加速器，QEMU能仿真至接近真实电脑的速度。QEMU有两种主要运作模式：

使用kqemu可使QEMU能仿真至接近实机速度，但其在虚拟的操作系统是Microsoft Windows 98或以下的情况下是无用的。

现时主要使用qemu-kvm替代kqemu进行guest系统加速。该组件稳定性与效率较kqemu有所提升。

QEMU (short for Quick Emulator) is a free and open-source hosted hypervisor that performs hardware virtualization (not to be confused with hardware-assisted virtualization).

QEMU is a hosted virtual machine monitor: It emulates CPUs through dynamic binary translation and provides a set of device models, enabling it to run a variety of unmodified guest operating systems. It also can be used together with KVM in order to run virtual machines at near-native speed (requiring hardware virtualization extensions on x86 machines). QEMU can also be used purely for CPU emulation for user-level processes, allowing applications compiled for one architecture to be run on another.