Flash drives adhering to the U3 specification are termed "U3 smart

drives" or "U3 smart technology". U3 smart drives come preinstalled

with the U3 Launchpad, which looks similar to the Windows OS start

menu and controls program installation,Applications which comply with

U3 specifications are allowed to write files or registry information

to the host computer, but they must remove this information when the

flash drive is ejected. Customizations and settings are instead

stored with the application on the flash drive,this type of system is

used to reduce the risk of virus infection while plug in to

computer,and which is easy to use ie Programs are run from the

Launchpad, functionally similar to the Windows Start menu familiar to

most users of Windows XP


read more
http://u3smart/default.aspx
http://en.wikipediawiki/U3