A machine readable medium carries operating software for use in a system which comprises the programmable device carrying at least one on-device file and/or application and an interface device for interfacing with the or each programmable device. The interface device is provided with at least one one-off device file and/or application; the operating software. The operating software enables, in use, the on-device and off-device files and/or applications to interface with one another and includes at least one file formatted in a web (Internet) standard language for self-describing messages, preferably XML. This file contains at least some of the file system and commands for accessing the file system which allow the on-device and off-device files and/or applications to interface. The interface device may be provided with at least one upgrade file in, for example, XML which contains an upgraded version of at least one on-device file and/or application and includes means for comparing the version of the on-device file or application on a particular programmable device with that in the upgrade file, upgrading the on-device file or application if the version on that device is earlier than that in the upgrade file. The interface device or the programmable device may, further, be provided with a file in web standard language which contains at least one configurable Security Environment. The system or device may include a plurality of files formatted in web standard language for self-describing messages, each of those files including a data model ("virtual card") corresponding to one of a plurality of different programmable devices, for example, smart cards of different kinds. The system may include means for configuring at least one of those virtual cards for downloading on to a memory-bearing programmable device. The system may further include at least one file in web standard language for self-describing messages capable of generating at least one APDU which, when run on a smart card, modifies or updates existing files or file structures.