What's the difference betweenn boot0.S and boot0ext.S

[pradeep tr]

Hi,
 I understand that from mbr.s we go for either boot0.s or boot0ext.s am I correct here? If yes when do we go for boot0.s or boot0ext.s?

or is it like that mbr.s 's advanced version is boot0.s and boot0ext.s and called by name boot manager ?so now mbr itself is in boot0.s or boot0ext.s.

--Regards,
trp