FreeMcBoot is a softmod installed on the memory card that works on nearly all Sony PlayStation 2s (except SCPH-900xx). FMCB allows the booting of homebrew, which in turn allows booting emulators and PS2 game backups from hard drive (if your PS2 supports it), ethernet, or USB.
While FMCB is very easy to use once it’s installed, getting the installer to run in the first place can get pretty complicated. Skip the hassle by buying a pre-installed FMCB memory card!
NOTE: The memory card you get may not be an official Sony memory card and may vary in size.