INT 15 - later PSIBM PS/2, any model/2s - WRITE BOOT DEVICE KEY AX = D601h BL = 01h DX = device ID Return: CF clear on success AH = 00h CF set on error AH = status (86h for function not supported) SeeAlso: AX=D600h/BL=01h,AX=D601h/BL=00h