An ATM controller (ATMC) is a system used in financial institutions to route financial transactions between ATMs, core banking systems and other banks. An ATMC is sometimes referred to as an "EFTPOS Switch." An ATM controller is key infrastructure in an interbank network. A message may enter an ATMC from an ATM, another ATMC or a third party. When receiving a message, the ATMC will examine the message, validate the PIN block if present, and then route the message according to the leading digits of the account number referenced.