A live USB is a portable

USB Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...

-attached external

data storage Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are con ...

device containing a full

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

that can be booted from. The term is reminiscent of

USB flash drive A flash drive (also thumb drive, memory stick, and pen drive/pendrive) is a data storage device that includes flash memory with an integrated USB interface. A typical USB drive is removable, rewritable, and smaller than an optical disc, and u ...

s but may encompass an external

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

solid-state drive A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently. It is sometimes called semiconductor storage device, solid-state device, or solid-state disk. SSDs rely on non- ...

, though they may be referred to as "live HDD" and "live SSD" respectively. They are the evolutionary next step after

live CD A live CD (also live DVD, live disc, or live operating system) is a complete booting, bootable computer installation including operating system which runs directly from a CD-ROM or similar storage device into a computer's memory, rather than lo ...

s, but with the added benefit of writable storage, allowing customizations to the booted operating system. Live USBs can be used in

embedded systems An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is em ...

for

system administration An IT administrator, system administrator, sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as servers. The system administr ...

data recovery In computing, data recovery is a process of retrieving deleted, inaccessible, lost, corrupted, damaged, overwritten or formatted data from computer data storage#Secondary storage, secondary storage, removable media or Computer file, files, when ...

, or test driving, and can persistently save settings and install software packages on the USB device. Many operating systems including , ,

Windows XP Embedded Windows XP, which is the next version of Windows NT after Windows 2000 and the successor to the consumer-oriented Windows Me, has been released in several editions since its original release in 2001. Windows XP is available in many languages. In ...

and a large portion of

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

and

BSD The Berkeley Software Distribution (BSD), also known as Berkeley Unix or BSD Unix, is a discontinued Unix operating system developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley, beginni ...

distributions can run from a USB flash drive, and Windows 8 Enterprise has a feature titled

Windows To Go Windows To Go was a feature in Windows 8 Enterprise, Windows 8.1 Enterprise, Windows 10 Education Windows 10 Enterprise and Windows 11 versions prior to the May 2020 update, that allows the system to boot and run from certain USB mass storag ...

for a similar purpose.

Background

To repair a computer with booting issues, technicians often use lightweight operating systems on

bootable media A boot disk is a removable digital data storage medium from which a computer can load and run (boot) an operating system or utility program. The computer must have a built-in program which will load and execute a program from a boot disk meeting c ...

and a

command-line interface A command-line interface (CLI) is a means of interacting with software via command (computing), commands each formatted as a line of text. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user ...

. The development of the first live CDs with graphical user interface made it feasible for non-technicians to repair malfunctioning computers. Most Live CDs are Linux-based, and in addition to repairing computers, these would occasionally be used in their own right as operating systems.

Personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...

s introduced USB booting in the early 2000s, with the

Macintosh Mac is a brand of personal computers designed and marketed by Apple Inc., Apple since 1984. The name is short for Macintosh (its official name until 1999), a reference to the McIntosh (apple), McIntosh apple. The current product lineup inclu ...

computers introducing the functionality in 1999 beginning with the

Power Mac G4 The Power Mac G4 is a series of personal computers designed, manufactured, and sold by Apple Computer from 1999 to 2004 as part of the Power Macintosh line. Built around the PowerPC G4 series of microprocessors, the Power Mac G4 was marketed by ...

with AGP graphics and the slot-loading

iMac G3 The iMac G3, originally released as the iMac, is a series of Macintosh personal computers that Apple Computer sold from 1998 to 2003. The iMac was Apple's first major product release under CEO Steve Jobs following his return to the financiall ...

models. Intel-based Macs carried this functionality over with booting

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

from USB. Specialized USB-based booting was proposed by IBM in 2004 with ''Reincarnating PCs with Portable

SoulPad SoulPad is a mobile computing project developed by IBM from 2004-2005. It enabled users to transfer their operating system between computers using a USB flash drive. Background The SoulPad project was introduced in a 2004 research paper titled ...

s'' and ''Boot Linux from a FireWire device''.

Benefits and limitations

Live USBs share many of the benefits and limitations of live CDs, and also incorporate their own.

Benefits

* In contrast to live CDs, the data contained on the

booting device In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) h ...

can be changed and additional data stored on the same device. A user can carry their preferred operating system, applications, configuration, and personal files with them, making it easy to share a single system between multiple users. * Live USBs provide the additional benefit of enhanced privacy because users can easily carry the USB device with them or store it in a secure location (e.g. a

safe A safe (also called a strongbox or coffer) is a secure lockable enclosure used for securing valuable objects against theft or fire. A safe is usually a hollow cuboid or cylinder, with one face being removable or hinged to form a door. The body ...

), reducing the opportunities for others to access their data. On the other hand, a USB device is easily lost or stolen, so data

encryption In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...

and

backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "wikt:back ...

is even more important than with a typical desktop system. * The absence of moving parts in USB flash devices allows true

random access Random access (also called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any other, no matter how many elemen ...

, thereby avoiding the

rotational latency Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: #Access time, access time and #Data transfer rate, data transfer time (o ...

and

seek time Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: #Access time, access time and #Data transfer rate, data transfer time (o ...

of hard drives or

optical media An optical disc is a flat, usuallyNon-circular optical discs exist for fashion purposes; see shaped compact disc. disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid o ...

, meaning small programs will start faster from a USB flash drive than from a local hard disk or live CD. However, as USB devices typically achieve lower data transfer rates than internal hard drives, booting from older computers that lack support for

USB 2.0 Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical i ...

or newer can be very slow.

Limitations

* Live USB OSes like

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed primarily of free and open-source software. Developed by the British company Canonical (company), Canonical and a community of contributors under a Meritocracy, meritocratic gover ...

Linux apply all filesystem writes to a casper filesystem overlay (casper-rw) that, once full or out of flash drive space, becomes unusable and the OS ceases to boot. * USB controllers on add-in cards (e.g. ISA, PCI, and PCI-E) are almost never capable of being booted from, so systems that do not have native USB controllers in their chipset (e.g. such as older ones before USB) likely will be unable to boot from USB even when USB is enabled via such an add-in card. * Some computers, particularly older ones, may not have a

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

that supports USB booting. Many which do support USB booting may still be unable to boot the device in question. In these cases a computer can often be "redirected" to boot from a USB device through use of an initial bootable CD or

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...

. * Some Intel-based Macintosh computers have limitations when booting from USB devices – while the

Extensible Firmware Interface Unified Extensible Firmware Interface (UEFI, as an acronym) is a specification for the firmware architecture of a computing platform. When a computer is powered on, the UEFI implementation is typically the first that runs, before starting th ...

(EFI)

firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...

can recognize and boot from USB drives, it can do this only in EFI mode. When the firmware switches to "legacy" BIOS mode, it no longer recognizes USB drives. Non-Macintosh systems, notably Windows and Linux, may not be typically booted in EFI mode and thus USB booting may be limited to supported hardware and software combinations that can easily be booted via EFI. However, programs like Mac Linux USB Loader can alleviate the difficulties of the task of booting a Linux-live USB on a Mac. This limitation could be fixed by either changing the Apple firmware to include a USB driver in BIOS mode, or changing the operating systems to remove the dependency on the BIOS. * Due to the additional write cycles that occur on a full-blown installation, the life of the flash drive may be slightly reduced. This doesn't apply to systems particularly designed for live systems which keep all changes in

RAM Ram, ram, or RAM most commonly refers to: * A male sheep * Random-access memory, computer memory * Ram Trucks, US, since 2009 ** List of vehicles named Dodge Ram, trucks and vans ** Ram Pickup, produced by Ram Trucks Ram, ram, or RAM may also ref ...

until the user logs off. A write-locked SD card (known as a Live SD, the solid-state counterpart to a live CD) in a USB flash card reader adapter is an effective way to avoid any duty cycles on the flash medium from writes and circumvent this problem. The SD card as a

WORM Worms are many different distantly related bilateria, bilateral animals that typically have a long cylindrical tube-like body, no limb (anatomy), limbs, and usually no eyes. Worms vary in size from microscopic to over in length for marine ...

device has an essentially unlimited life. An OS such as Linux can then run from the live USB/SD card and use conventional media for writing, such as magnetic disks, to preserve system changes; .

Setup

Various applications exist to create live USBs; examples includ
Universal USB Installer

Rufus Rufus is a masculine given name, a surname, an Ancient Roman cognomen and a nickname (from Latin ''wikt:rufus, rufus'', "red"). Notable people with the name include: Given name Politicians * Marcus Caelius Rufus, (28 May 82 BC – after 48 ...

, Fedora Live USB Creator, and

UNetbootin UNetbootin ("Universal Netboot Installer") is a cross-platform utility that can create live USB systems and can load a variety of system utilities or install various Linux distributions and other operating systems without a CD. Modes USB ins ...

. There are also software applications available that can be used to create a Multiboot live USB; some examples includ
YUMI Multiboot Bootable USB Creator
and

Ventoy Ventoy is a free and open-source utility used for creating bootable USB media storage devices with files such as .iso, .wim, .img, .vhd(x), and . Once Ventoy is installed on a USB drive, new installation files can be added without reformattin ...

. A few

Linux distribution A Linux distribution, often abbreviated as distro, is an operating system that includes the Linux kernel for its kernel functionality. Although the name does not imply product distribution per se, a distro—if distributed on its own—is oft ...

s and live CDs have ready-made scripts which perform the steps below automatically. In addition, on Knoppix and Ubuntu extra applications can be installed, and a persistent file system can be used to store changes. A base install ranges between as little as 16 MiB (

Tiny Core Linux Tiny Core Linux (TCL) is a minimal Linux kernel based operating system focusing on providing a base system using BusyBox and FLTK. It was developed by Robert Shingledecker, who was previously the lead developer of Damn Small Linux. The distribu ...

) to a large DVD-sized install (4 gigabytes). To set up a live USB system for commodity PC hardware, the following steps must be taken: * A

needs to be connected to the system, and be detected by it * One or more partitions may need to be created on the USB flash drive * The "bootable" flag must be set on the primary partition on the USB flash drive * An MBR must be written to the primary partition of the USB flash drive * The partition must be formatted (most often in

FAT32 File Allocation Table (FAT) is a file system developed for personal computers and was the default file system for the MS-DOS and Windows 9x operating systems. Originally developed in 1977 for use on floppy disks, it was adapted for use on ...

format, but other file systems can be used too) * A bootloader must be installed to the partition (most often using syslinux when installing a Linux system) * A bootloader configuration file (if used) must be written * The necessary files of the operating system and default applications must be copied to the USB flash drive * Language and keyboard files (if used) must be written to the USB flash drive * USB support in the BIOS’s boot menu (although there are ways to get around this; actual use of a CD or DVD can allow the user to choose if the medium can later be written to.

Write Once Read Many Write once read many (WORM) describes a data storage device in which information, once written, cannot be modified. This write protection affords the assurance that the data cannot be tampered with once it is written to the device, excluding the ...

discs allow certainty that the live system will be clean the next time it is rebooted.)

Knoppix Knoppix, stylized KNOPPIX ( ), is an operating system based on Debian designed to be run directly from a CD or DVD (Live CD) or a USB flash drive ( Live USB). It was first released in 2000 by German Linux consultant Klaus Knopper, and was one ...

live CDs have a utility that, on boot, allows users to declare their intent to write the operating system's file structures either temporarily, to a

RAM disk A RAM drive (also called a RAM disk) is a block of random-access memory ( primary storage or volatile memory) that a computer's software is treating as if the memory were a disk drive (secondary storage). RAM drives provide high-performance te ...

, or permanently, on disk or flash media to preserve any added configurations and security updates. This can be easier than recreating the USB system but may be moot since many live USB tools are simple to use.

Full installation

One alternative to the live operating-system solution would be a full installation; that is, a traditional installation, but without swap partitions. This option has the advantage of being efficient for the software, as it eliminates the need for the device to retain – separate from the persistent file – the operating-system’s installer software. However, full installation is not without disadvantages; due to the additional write cycles that it requires, the life of the flash drive may be slightly reduced. To mitigate this, some ''live'' systems are designed to store changes in RAM until the user initiates a system powerdown, which triggers the actual writes to the device. The trade-off is greater risk of lost work, in the case of an abnormal abort. Beyond these, another factor to consider is that, if the transfer speed of the storage device is poor, then performance can be reduced to a rate more typical of legacy computers – even for machines with modern components. This issue can usually be overcome by installing to a USB hard drive, as they generally perform better than flash drives, regardless of the connector.

Microsoft Windows

Although many live USBs rely on booting an open-source operating system such as Linux, it is possible to create live USBs for Microsoft Windows by using

Diskpart In computing, diskpart is a command-line interface, command-line disk partitioning utility included in Windows 2000 and later Microsoft operating systems, replacing its predecessor, fdisk. The command is also available in ReactOS. Overview T ...

WinToUSB Windows To Go was a feature in Windows 8 Enterprise, Windows 8.1 Enterprise, Windows 10 Education Windows 10 Enterprise and Windows 11 versions prior to the May 2020 update, that allows the system to boot and run from certain USB mass storag ...

References

External links

The Differences Between Persistent Live USB and Full Linux Install on USB

Universal USB Installer

Tutorial – How to Set your BIOS to boot from CD or USB

HOW TO: Create a working Live USB

Debian Live project

How to create a Live USB in Ubuntu

Hiren's Boot USB
{{Operating System USB