roles of grub-install and grub-setup?

[rob wilco]

Hello list,

I want to boot a system laying on lvm, on an intel mac mini, I used :

# grub-mkimage -o /boot/grub/core.img pc lvm ext2

Q1 : Are the cited modules sufficient? Does the 'pc' module means someting like BIOS or MBR partition table?

Q2 : What is the difference between grub-install and grub-setup? What is their respective role?
They both seem to alter the mbr.
 - I did a checksum of the MBR 
 - then I used grub-setup and the MBR checksum changed
 - then I used grub-install and the MBR checksum changed again

Here are the details

# dd if=/dev/sda count=2  2> /dev/null | md5sum
1e97dbbfd7a2edcffb858318ddf1a554  -

# grub-setup /dev/sda
# dd if=/dev/sda count=2  2> /dev/null | md5sum
a7afaf2c2c65fde00c1696d34def882f  -

# grub-install /dev/sda > /dev/null
# dd if=/dev/sda count=2  2> /dev/null | md5sum
1e97dbbfd7a2edcffb858318ddf1a554  -

# grub-setup /dev/sda
# dd if=/dev/sda count=2  2> /dev/null | md5sum
1e97dbbfd7a2edcffb858318ddf1a554  -

# grub-install /dev/sda > /dev/null
# dd if=/dev/sda count=2  2> /dev/null | md5sum
1e97dbbfd7a2edcffb858318ddf1a554  -

Thanks,