QEMU (short for Quick Emulator) is a free and open-source hosted hypervisor that performs hardware 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.
qemu-img create -f qcow2 image.img 5G qemu-system-i386 -hda image.img -cdrom image.iso -boot d -m 2047 -net nic -net user -enable-kvm qemu-system-i386 -hda image.img -m 2047 -enable-kvm -net nic -net user -soundhw ac97