One opportunity for Westpac and St George in a merger is that it presents both with a business case at long last to send their existing core banking system and associated apparatus to the scrap merchant. In the short term Westpac will no doubt simply migrate most of St George's banking products onto the former's information systems. Not that there's anything notable about the IT systems of Westpac (other than, perhaps, their ability to string together disparate systems to maintain a degree of product innovation).Both banks operate on core legacy systems, a mix of Hogan, CSC, IBM, Solaris, Oracle and home-grown code.St George has at least 300 discrete information systems and Westpac probably has more.The external guessing at this stage is that Westpac would use the takeover as the trigger for a major investment in IT, or "a complete systems overhaul" as some consultants put it.While this sort of investment is of a "stay in business" nature, and arguably overdue, it will also eat into the savings Westpac can extract from St George.