The bhyve ATA/ATAPI emulation is part of a larger project that aims to insure backward compatibilty with older versions of FreeBSD guests for FreeBSD Hypervisor (bhyve). Currently the bhyve hypervisor emulates AHCI standard for drive and atapi devices. In order to support guests like FreeBSD 4 that does not have ahci drivers, it is necessary to emulate an ATA/ATAPI controller.