The QEMU emulator allows you to simulate your hardware while running your application or image. QEMU is made available a number of ways:
If you use the ADT Installer script to install ADT, you can specify whether or not to install QEMU.
If you have downloaded a Yocto Project release and unpacked it to create a Source Directory and you have sourced the environment setup script, QEMU is installed and automatically available.
If you have installed the cross-toolchain tarball and you have sourced the toolchain's setup environment script, QEMU is also installed and automatically available.