Senior deputy collector aur Sdm me kya difference hai?? aur State me sirf Deputy collector hota hai lekin bihar me senior deputy collector kyu?? senior deputy collector kaise sdm banta hai?? kya senior deputy collector ak sub-division kaa head hota hai?? plz Ans in detail
SDM is Sub-divisional magistrate while Senior deputy collector that id ADM i.e. Additional District Magistrate who is just after the DM i.e. District Magistrate or collector.
Now, here SDM is responsible only for a Revenue division or Sub-division or Sub-district. And, he is below ADM as he is responsible for whole district. In bigger cities like Patna we also have a post between collector and ADM that is Senior deputy collector of which you are talking. The work of three of these personalities is almost the same but in larger city one or two people are not sufficient for all the handling and management. Obviously, by promotion SDM becomes ADM and above.
Feel free to ask doubts in the Comment Section.
I hope this information helps you.