U3, first brought to market in 2005 by San-Disk, is the oldest and best known of the three, appearing in almost all of Sandisk's flash drives since it was launched. U3 works by mounting a virtual CD-ROM drive in addition to the main storage partition. The virtual CD-ROM would then trigger Windows' Autorun and execute a "LaunchPad" in the System Tray to provide quick access to applications and data housed on the flash drive.