Kernel Question

I need some help from you kernel warriors.

I just changed my root filesystem from reiserfs to ext3
(tar -c, mke2cf, tar -x), rebooted, and it worked fine.
I expected problems. I know, why look a gift horse in
the mouth?

Here's the weird part - /etc/fstab still showed my root filesystem
is reiserfs:
/dev/hdc3       /                       reiserfs        defaults   1   1

and running mount verified it was mounted as reiserfs.

I changed /etc/fstab:
/dev/hdc3       /                       ext3            defaults   1   1

rebooted, went through a long fsck (no errors), and now it it mounted
as ext3, verified by mount.

How does the kernel know which filesystem to use when looking for
/etc/modules.conf and /etc/fstab?

George