Files that contain the .sisx file extension are installer files for mobile devices that use the later versions of the Symbian operating system. They are referred to as Symbian Series 3 installation packages.
The SISX files define the way the applications are installed on the Nokia phones that operate on the Symbain operating system. Prior to Symbian version OS 9.1, the installer files were saved as .sis files. Once Symbian OS 9.1 was released the files were saved with the .sisx extension. This file format makes it easier and more convenient to distribute and install applications onto the Symbian-operated device.
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