You will probably need to edit the boot loader configuration file. If you are using the boot loader from Mac, the file to modify is “/Library/Preferences/SystemConfiguration/com.apple.Boot.plist”
P.s. Be careful when editing this file.
ooooopppssss thats not the best way, you might damage the Mac OS like that, only u have to do that is go to “system preferences” and then open “startup Disk” from there u can select ur desire drive for Boot. which will boot automaticaly……..enjoy it