Q How do you install an OS from a USB flash drive?

A Use a utility to create a bootable USB then set your BIOS to boot from it.

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First you need an Operating System (OS) installation ISO, this single file is an archive that contains the required OS files. The ISO needs to be transferred to the USB flash drive using a utility that depends on both your operating system and the target operating system. For windows installations the Microsoft Windows 7 USB/DVD download tool is straightforward to use (it also works with Windows 8). Download and install the utility, then run it and follow the instructions, it will ask you which ISO to use and which USB drive to burn it onto. For Linux there are equivalent tools detailed in the Ubuntu help pages. Once you have your bootable USB flash drive, the next task is getting your target PC to boot from it. There is usually a setting in the BIOS (press the del or f8 key shortly after power on) which allows you to set USB as one of the boot devices. Additionally, during PC startup, it is often possible to press a hotkey (MB dependent) which allows you to choose a boot device.

Compatibility

Not all motherboards allow booting from all USB flash drives as there has to be compatibility between the two. Because operating system installation requires large data transfers it is desirable to use USB 3.0 which speeds things up significantly. We have found that it's relatively difficult to get USB 3.0 connection speeds during boot. A drive that has worked well for us is the Kingston DT G2 Ultimate but unfortunately this drive has been superseded and is now difficult to find in most countries. Other USB 3.0 drives that have been used with relative success include the Jetflash 700, there are additional recommendations and useful information in this forum post.