"*.iso" files are CDROM images in ISO 9660 format, and should be bootable for most architectures. "*.install.img.gz" files are bootable disk images intended to be written to USB drives, or any other disk which would appear as "sd0". NetBSD can then be installed on the main system. "*.xva.zip" files are images for XenServer or Xen Cloud Platform. See README.xva .