QEMU is a fast, cross-platform open source machine emulator which can emulate a huge number of hardware architectures for you. QEMU lets you run a complete unmodified operating system (VM Guest) on top of your existing system (VM Host Server).

You can also use QEMU for debugging purposes—you can easily stop your running virtual machine, inspect its state and save and restore it later.

QEMU consists of the following parts:

QEMU is central to KVM and Xen Virtualization, where it provides the general machine emulation. Xen's usage of QEMU is somewhat hidden from the user, while KVM's usage exposes most QEMU features transparently. If the VM Guest hardware architecture is the same as the VM Host Server's architecture, QEMU can take advantage of the KVM acceleration (SUSE only supports QEMU with the KVM acceleration loaded).

Apart from providing a core virtualization infrastructure and processor-specific drivers, QEMU also provides an architecture-specific user space program for managing VM Guests. Depending on the architecture this program is one of:

In the following this command is called qemu-system-ARCH; in examples the qemu-system-x86_64 command is used.