U3 LLC is a joint venture that is backed by Sandisk and its subsidiary, M-Systems. U3 is accountable 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 (i.e., it can be run without first being installed on the computer). 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. Customizations and settings are instead stored with the application on the flash drive which allows one to run software on any computer with the same settings.

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.

The U3 platform

Hardware

U3 smart drives are USB flash drives with a specific hardware and software setup:

The hardware configuration causes Windows disk management to show two drives:

A read-only ISO 9660 volume on an emulated CD-ROM drive with an autorun configuration to execute the U3 LaunchPad, and

A standard flash drive (FAT formatted) that includes a hidden "SYSTEM" folder with your installed applications.

U3 compliant applications can be (optionally) preloaded by manufacturers.

U3 Launchpad

U3 Launch Pad example.

The U3 Launchpad is a program manager that is preinstalled on every U3 smart drive, and is set to autoplay on insertion. A partition with the U3 Launchpad pretends to be a CD/DVD-ROM device in order to add USB mass storage device autoplay functionality on pre-Windows XP SP2 systems, or systems whose USB autoplay has been intentionally disabled.

The program is made to work with Windows 2000 Service Pack 4 and above. No Launchpad program exists for the Mac OS or Linux platforms.

U3 applications

To be fully U3 compliant, an application has to be programmed to clean up its own data from the local machine. It must also be packaged in U3's special program format. U3 applications will only run from a U3 device. These apps may be hacked to run from other USB drives with the U3 Launchpad

APIs

The U3 APIs allows U3 Programs lower-level access to USB flash drive.

Compatibility

The U3 Launchpad and U3 Applications runs on Windows 2000 SP4+, XP or newer. The U3 launchpad will work with Windows Vista as of version 1.4.0.2. Data will continue to be accessible from any OS capable of reading from USB Mass Storage Devices, unless the U3 device is password-protected. Compatibility issues have been noted as late as July 2007 under Windows XP Pro between certain Windows drivers that are associated with high-volume data transfers to CD writers and with certain drivers employed by digital video cameras, resulting in a full crash of the XP operating system. According to Sandisk's community forums , as of Feb '08 many users are still exhibiting Vista compatibility issues with U3 equipped cruzers regardless of the U3 launchpad version. Apparently this is related to specific hardware/firmware versions of the cruzer itself , as removing the U3 software will still not allow Vista to recognize the USB key. While Sandisk has claimed that a patch for the U3 is in the works, Microsoft has released an update to Vista (KB940199) , allowing some users to successfully use the cruzer as intended.

Developer resources

Information on building U3 compliant applications and the U3 software development kit, are available to registered developers at the official U3 website. Individuals must register (as a company) to download the SDK, or participate in the forums.

The software itself can be removed by reformatting the drive to FAT32 by any Windows 2000/XP, Linux or OSX system. Benefits

PortabilitySoftware can be taken with all its personalized settings to any computer running a compatible version of Microsoft Windows, with no need to install the software if not already there, or to use different settings and options, and no need for administrator access privileges.
Software supportSoftware is available from the U3 site, including amongst others Trillian (instant messaging client), OpenOffice.org, FileZilla, Mozilla Firefox, and Skype. Some recent software compatibility concerns have surfaced, including incompatibility of newer Firefox versions with U3. However, updated versions of programs have made an appearance, like in the case of Mozilla Firefox.
Ease of usePrograms are run from the Launchpad, functionally similar to the Windows Start menu familiar to most users of Windows XP.
No need of admin rightsNew software can be downloaded to a U3 flash drive without the requirement for administrative privileges on the host computer. However, removal of the U3 launchpad requires administrative rights.
Virus protectionMany U3 drives come with virus protection software which gives protection against being infected by or spreading computer viruses.
3rd party supportSome popular free portable application programs available at PortableApps.com for non-U3 flash drives have been adapted for use with U3 drives. They are available at the web sites of U3 and PortableApps.com.
Data SecurityMost U3 drives on the market feature a security lock within the U3 Launchpad. This loads the CD partition first and can be user-configured to require a password to be entered; otherwise the data partition will not load. The drive is supposed to seal itself after a certain number of invalid password entries, requiring a reformat.

Criticisms

Several criticisms have been completed of the U3 platform. These criticisms are:Freezing the ComputerStrong possibility of locking up or freezing a computer with certain software installed. In general it is a result of a conflict with popular CD/DVD burning software according to a FAQ by U3. The posted list includes software provided by Nero and Roxio. Even on computers where U3 functions properly, there can be a noticeable delay while the Launchpad loads compared to the time it takes to access a normal USB flash drive.
Closed PlatformThe U3 platform is closed, though is available to anyone who registers (for free) with U3. Sandisk, the rights holders for U3, ask for a 5% royalty from USB flash drive manufacturers who wish to implement the platform on their products.
Uninstallation issuesThe original U3 Launchpad could not be uninstalled by an end-user. U3 responded to this criticism by making uninstall software available on their website. This was largely due to Best Buy's Geek Squad, who in early 2006 raised the issue of not being able to uninstall U3 and got them to first write an uninstaller for the Geek Squad branded drives, and later for all the U3 drives; as of November 2006, U3 drives come with an uninstaller on the USB drive itself. However, the uninstaller doesn't work in all cases ; and requires installing proprietary software on the computer before being able to remove the U3 features from the flash drive . Although U3 removal disables U3 functionality, SanDisk does offer LPInstaller to reinstall the basic U3 feature-set.
Leaves Traces on Host PCThe U3 platform sometimes leaves behind files on a user's PC. This mainly occurs when the drive is improperly removed.
Insufficient user privilegesWhere a user has insufficient privileges, he or she may run into problems getting the launcher to work . In such a case the launcher might actually prove a hindrance to using the device .
Two Drive LettersAs a work-around to the lack of Auto-Play for Flash drives on older versions of Windows, the U3 software creates two drive letters (one which presents itself as a CD to allow Windows' auto-play to start the launcher, and another for storing user data). Although this is the only way to implement auto-start functionality on pre-Windows XP systems, it could be thought of a kludge, and the extra drive letter created can be an annoyance.
Windows requirement for removalUsers of non-Microsoft OSes that do not have access to a Windows PC are unable to remove U3 from their "smart drives."

Modification

The Launchpad software on a U3 device can be replaced using 3rd party tools, allowing it to Autoplay any software that is able to fit onto the device. This involves creating an ISO image and then transferring the ISO image onto the device, replacing the existing Launchpad files. Universal Customizer is an example of such a tool.

Future

Sandisk and Microsoft have recently announced a partnership to develop a new line of portable USB-based hardware. This series, currently unnamed, is expected to replace U3 by the end of 2008, making the U3 format obsolete.