yoshi314 explained it, but it is a "multi install" and not a "multi-boot".
Originally Posted by r3ap3r
It installs dummy-files, to give compatibility to all PS2-versions&revisions of the same region.
It has nothing to do with "multi-boot" (which name implies, that you have the choice of which osd-update you boot [but there is no choice]).
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux