The new ExtremeSwitching X870 series switches use the Open Network Install Environment (ONIE) Bootloader.
ONIE is an open source initiative driven by a community of next-generation networking vendors to define an open “install environment” for bare metal network switches. ONIE acts as an enhanced bootloader using facilities in a Linux/BusyBox environment. The ONIE Bootloader provides all the standard capabilities, including rescue capability, multiple image selection, etc.
For more information, see http://onie.org.