Microsoft unleashed another version of Windows - Windows 8, for public testing on Wednesday in an effort to win back some of the ground it has been losing to Apple and Google. The upcoming touch-based Windows 8 operating system was introduced at the Mobile World Congress in Barcelona, the planet\'s largest cell phone trade show. Quite different from its predecessors, Windows 8 doesn\'t have the traditional \"Start\" menu and applications are spread across a mosaic of tiles in a design Microsoft calls \"Metro.\" The tiles, which resemble road signs, can be navigated with a finger swipe on the screen or with a keyboard and mouse. The new operating system works on tablets as well as PCs and laptops, connecting them via the cloud to give users a more consistent experience as they switch between devices. The system is expected to powers up on PCs in eight seconds, much faster than the previous version. An internet \"Windows Store\", where users can download applications for the operating system, was also launched on Wednesday. Apps will be free to download for the duration of the consumer preview, but would include both free and paid versions after the operating system is released.