Booting up your Hackintosh for the first time is very complex process which often requires special boot option through the boot flag.Boot flag is a the predefine keyword by apple developer to troubleshoot there hardware with respect to software and there just are “arguments” (pieces of input data that you enter) to change the way that your boot loader runs. The boot loader is the program that boots Mac OS X like Chameleon,Chimera and Clover
“UHCIReset=Yes ” / “USBLegacyOff=Yes ” This flags are also fix USB related issue.
“nvda_drv=0” This flag is basically use the OS X Native driver instead of NVIDIA Cuda/Web driver
for target model (search it on google).
“kext-dev-mode=1” this flag is necessary in OS X 10.10 Yosemite without of it you will never get installation screen.
“-xcpm” This flag is use to read the mac_kernel to newer Haswell processors to avoid instant reboot basically this solve mismatched error of the P-state and C-state
“-force64” this flag is use to boot x86_64 mode in other words by using this we can boot our OS X directly in 64 bit mode (usable in only 10.6.X to10.7.X) because (10.8.X to 10.10 this are support only 64 bit)
“arch=i386” this flag use to boot in x86 (64 bit) mode.