Hello Aspirant,

See All India Rank is allotted to each and every JEE-Advance qualifier through which admission is made to 4-year UG B.Tech programme in IITs but on the other hand preparatory rank is the rank through which student gets admission in preparatory course offered by IITs.

Now let us discuss what is preparatory course. If you have been allotted a preparatory rank then you can take admission in any particular branch in IITs for which you will be eligible according to cut-offs  and then you will be prepared for one year for that particular course and after the successful completion of that course you will be either considered as pass or fail. If you will pass that course than you will be directly get admitted to that branch for next 4-years to complete your B.Tech without appearing for JEE-Advance again but if you want to appear again for JEE-Advance then you can.

I hope this information helps you.

Good Luck!!