Simulink Real-Time runs OnTime RTKernel on DOS. MS-DOS or FreeDOS require a BIOS interface to boot. Thus it's not possible for UEFI firmware to boot DOS. However, some UEFI firmware support a "Legacy BIOS" boot mode option in settings screen. When enabled it becomes possible to boot DOS, but any other installed OS will be unbootable until you return to UEFI mode. Intel will remove Legacy BIOS boot support from UEFI by 2020, and many motherboards are already released which are UEFI only without any support for "Legacy BIOS". So you have to be carefull picking your motherboard if you want it to run Simulink Real-Time.