CardOS is an operating system developed by Siemens for chip cards and smart cards, whereby the product designation CardOS/M indicates the use in multifunction cards.
In general, the operating systems, whether for personal computers (PC) or smart cards, are stored in ROM. The operating system determines the applications and functions that are assigned to the smart card. For example, as a cash card, signature card with digital signature, SIM card for a mobile phone or for other applications. These applications are identified with an application ID. In addition, the CardOS operating system manages the directories and file systems, deleting, writing and reading and protects the files from unauthorized access.
CardOS meets the requirements of the German Signature Act (SigG) and, thanks to its flexibility, can directly support new card applications. Loadable software modules allow the extension and adaptation of the operating system with regard to special applications. Almost all functions of the operating system can be parameterized.
CardOS/M4 is based on the Infineon processor SLE66CX with cryptography controller. The command structure is in accordance with ISO 7816.