On these systems, the firmware password is stored as a PRAM variable in which the password is simply obfuscated.
The Firmware Password Utility is by default in the Utilities menu on the recovery partition or on the OS X install disc, and may not be available if you cannot boot to these volumes. Unfortunately in these cases for newer Mac systems shipped in 2011 or later, you have to get the system serviced to reset the password however, if you own a system from before 2011, then you can retrieve a forgotten password, provided you have admin access to the system. While this can be done using Apple's Firmware Password Utility on the recovery drive or OS X installation disc, there may be times when you do not have access to this drive either because it is missing or corrupted, and therefore cannot use the password utility. A firmware password on Mac systems locks the hardware to prevent booting to alternative modes that could bypass OS X security, but in order to access some of these modes you first have to disable the firmware password.
