mac用的比WIN早  LINUX最早

Apple–Intel[edit]
On Apple–Intel architecture Macintosh computers, the EFI partition is initially blank and not used for booting.[9] However, the EFI partition is used as a staging area for firmware updates;[10] specifically, it places a firmware flash utility (EFI binary) and data file (FD – "Firmware Device"[11]) in the directory EFI/APPLE/FIRMWARE which is then run when rebooting the system in "flash firmware" mode.[12]
If deleted, the system will still boot, and the boot manager will still allow users to choose whether to start a Boot Camp partition or the default Mac OS X, but firmware updates will fail.
http://en.wikipedia.org/wiki/EFI_System_partition

OS X 并不使用EFI启动系统。只是在Fireware升级的时候，把EFI用来存储新的Fireware。如果该分区删除掉，OS X依然能够启动，但是无法进行固件升级了。