What is Differnece between the Interfaces and BDC'S??
Interface, a program or group of programs that handle the passing of data from one system to another. These programs work together to export the data from one system and import into a target system, maybe these programs run once a day, maybe twice, may every hour throughout the day. It is a good way to keep the data in two or more systems in sync with each other.
Interfacing is connecting two or more different entities. In our case, it is connecting one or more systems with SAP. Now extending our previous example, you are replacing some legacy applications but there are some applications that you don't want to replace yet. You need to somehow pass data back and forth between SAP and these remaining systems. Data may be going one way or the other way or both ways. You will still need to do some data transformations/translations etc to make the data understandable to the receiving system. This will continue as long as you want to keep the systems running alongside SAP.
Interfaces are written to exchange/update/send/receive data between SAP and other systems on an ongoing basis. These can be in many forms, file based, idoc based, real time(business connector, XI etc are useful in this), xml, and the list goes on.
Interface and Conversion program with BDC are same.
Only the difference in the mode of execution.
BDC is used to upload data from legacy to SAP