A USB image — is bootable

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...

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

(OS) or other software where the

boot loader A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, an ...

is located on a

USB flash drive A USB flash drive (also called a thumb drive) is a data storage device that includes flash memory with an integrated USB interface. It is typically removable, rewritable and much smaller than an optical disc. Most weigh less than . Since fir ...

, or another

USB device Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

(with memory storage) instead of conventional CD or

DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kin ...

discs. The

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

loads from the USB device either to load it much like a

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

that runs OS or any other software from the storage or installs OS itself. USB image runs off of the USB device the whole time. A USB image is easier to carry, can be stored more safely than a conventional CD or

. Drawbacks are that some older devices may not support USB booting and that the USB storage devices lifespan might be shortened. Ubuntu has included a utility for installing an operating system image file to a USB flash drive since version 9.10. Windows support also has added a step by step on how to set up a USB device as a bootable drive.

Software

Both graphical applications and command line utilities are available for authoring bootable operating system images. dd is a utility commonly found in

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

operating systems that allow creation of bootable images.

Benefits and limitations

Benefits

* In contrast to live CDs, a USB image is easier to transport and to store (e.g. a pocket, attached to a key chain, carried in a bag, locked away in a safe), instead of a CD, which can be damaged and corrupted easier, and also harder * Also after OS installation, the USB can be removed after installation, and the operating system will run without the USB stick inserted into the computer, allowing installation on multiple OS devices with a single USB (This is known for Win 8.1 and newer Microsoft Win versions, since they fully support the USB image installation) * The absence of moving parts in USB flash devices allows true

random access Random access (more precisely and more generally 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 othe ...

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 and data transfer time (or rate). Access time The ''access ...

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 and data transfer time (or rate). Access time The ''acce ...

, meaning small programs will start faster from a USB flash drive than from a local hard disk or

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

. However, as USB devices typically achieve lower data transfer rates than internal hard drives, booting from older computers that lack

USB 2.0 Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

or newer can be very slow.

Limitations

* Some older systems have limited support for USB, since their BIOSes were not designed with such purpose at the time. Other devices may not be booted from USB, if in BIOS it is set to 'Legacy mode'

Legacy mode In computing, legacy mode is a state in which a computer system, component, or software application behaves in a way that is different from its standard operation in order to support older software, data, or expected behavior. It differs from back ...

. * Due to the additional write cycles that occur on a full installation, the life span of the used USB may be shortened. To mitigate this, a USB hard drive can be used, as they give better performance than the USB stick, regardless of the connector.

References

Booting {{Computer-stub

Software

Benefits and limitations

Benefits

Limitations

See also

References