Cloudow: A SaaS runtime system based on the user-level virtu-alization technology

SaaS is a promising mode for software delivery and usage across the Internet, which eliminates the need of users to purchase, maintain and upgrade software to a large extent. This paper proposes a new SaaS mode for legacy Windows software and its prototype, Cloudow. Cloudow enables ordinary users of Windows PC to use legacy desktop software from the Internet without installation, and the system supports to restore the users personal software con gurations on another PC. User-level virtualization technology is employed to enable legacy software to run without installation. Moreover, an on-demand delivery method based on the user-space le system is adopted, so the user can launching the remote software just as launching the local counterpart. Compared with the existing SaaS modes (like the VM-based solution and the Web applications), the legacy software can run on the client end directly while stored on the remote site, which gets good balance between compatibility and performance. Furthermore, aggressive pre-fetch mechanisms (including metadata/data/ le pre-fetch) and caching technologies are employed to improve the IO access performance remarkably. The tests show that for much common software, the runtime overhead is about 12%-20%.