COS (Card Operating System) is a sequence of instructions permanently embedded in the ROM of the smart card. COS manages the internal file system, I/O and the interactions between these components and various applications. Usually this operating system also contains most of the security services – handling encryption/decryption and managing security certificates. They provide functions for data and command exchange, data storage, data processing, cryptographic processes and more. ,The combination of card OS and all code committed to ROM is often referred to as the ROM “Mask” of an integrated smart card security chip.