initrd -- boot process doubt

[Edson Noboru Yamada]

On a machine with a SCSI controller, the kernel does not necessarily
need to have
its driver compiled -- instead, the initrd.img is loaded and over
there the kernel
can find a module that recognizes the SCSI controller.

My doubt is: how linux can load the initrd.img if, before that, it has
to read it off the disk
(but without the controller driver)? I suppose there is a very minimal
and generical driver that
works with every scsi controller and it's embedded in the kernel -- is
that right?

TIA