The form of the application passed to the target hardware is the Symbian Installation System (.SIS) file. The .SIS file is a compressed archive file that contains all the files required to install, and also includes option information for the installation process. The Symbian Installation System provides a simple and consistent user interface for installing applications, data, or configuration information to devices based on the Symbian operating system. The components installed by the developer (or end user) are included in the .sis file.
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C SDK SYMBIAN Development Getting Started