U3 LLC. is a joint venture that is backed by Sandisk and M-Systems. U3 is responsible for the development of a proprietary application design specification created for Microsoft Windows operating systems so that applications can be executed directly from a specially formatted USB flash drive. Applications are allowed to write files or registry information to the host computer, but this information must be removed when the flash drive is ejected.

USB flash drives adhering to the U3 specification are termed “U3 smart drives” by U3.com. “U3 smart drives” differ from traditional USB flash drives because they come preinstalled with the U3 Launchpad, which emulates the Windows OS start menu, and controls program installation.

[source:'wikipedia']