MBR during a boot scan.
I think you mean MFT
I think your right about it being the MFT (which does get fragmented).
@ Dch48
However, I'm not sure if it is able to defrag the MFT, or not as I do occasionally run it as defrag on boot, I still have 2 fragments for MFT and Registry on my XP Pro system in the C:\ partition.
I must try another boot-time defrag on this XP system and see if that has changed.
EDIT: just checked this out with the latest Puran Defrag and the boot-time defrag does indeed defrag the MFT and Registry.