A live USB is a USB flash drive or a USB external hard disk drive containing a full operating system that can be booted. Live USBs are closely related to live CDs, but sometimes have the ability to persistently save settings and permanently install software packages back onto the USB device. Like live CDs, live USBs can be used in embedded systems for system administration, data recovery, or the testing of operating system distributions without committing to a permanent installation on the local hard disk drive. Many operating systems including Mac OS 9, Mac OS X, Microsoft Windows XP Embedded and many of the Linux distributions and BSD distributions can also be used from a USB flash drive. Windows 8 is also capable to run from a USB drive, with Windows To Go.

Since 1999, Apple Macintosh computers (beginning with the Power Mac G4 with AGP graphics and the slot-loading iMac G3 models) have been able to boot from USB. Intel-based Macs support booting Mac OS X from USB.

Specialized USB-based booting was proposed by IBM in 2004, in the papers "Reincarnating PCs with Portable SoulPads" (PDF & Summary) and Boot Linux from a FireWire device.

Live may refer to:

Universal Serial Bus (USB) is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication and power supply between computers and electronic devices.

USB is not a true bus, meaning only the root hub sees the entire electrical communications. Or, there is no method to monitor upstream communications from a down stream device.

USB was designed to standardize the connection of computer peripherals, such as keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices.

As of 2008^[update], approximately 6 billion USB ports and interfaces were in the global marketplace, and about 2 billion were being sold each year.