How to Install Windows 8 From a USB Drive

Now that Windows 8 has hit the RTM stage and Microsoft published the final bits on TechNet and MSDN today, lots of people will be getting it from different places and begin installing it on their computers.
The most used way of installing a operative system today is from USB drives instead of optical media. The most important reason to this is, among others, the speed of installation and how easy it is to maintain your source files up to date. You can save yourself some time by installing from USB.
This article will cover the process of preparing your USB so you can install Windows 7/8 from it.The result will be a USB drive that can be used to install Windows 8, Windows 7 and Windows Vista.

Preparing the drive

Open a command-prompt window. You can do this by typing CMD in the Start Menu and pressing Enter afterwards. I use a program called PowerCmd for all my command-line needs, but you can use Windows built-in utility.
Diskpart is a command-line utility already built-in into Windows that allows you do many things with your hard disk and other drives. You can delete/create partitions, format disks, assign drive letter and more.
Type diskpart and the utility will start right away. The list disk command will list all available disks in your system. In my case, the USB drive is listed as number 5.

Make sure you select the correct drive number! You can delete important data by mistake.

• Select the correct drive. Type select disk X, where X is your USB drive.

• Delete all existing partitions on your drive. Type clean.

• Create a new primary partition. Type create partition primary.

• Select the new partition to work with. Type select partition 1.

• Mark the partition as active (bootable). Type active.

• Format the partition as NTFS. Type format fs=ntfs quick label=”Win8″.

• Assign a drive letter to your drive. Type assign.

• Exit Diskpart. Type exit.

That’s it. The drive is already formatted and marked as active so you can boot from it.

Copying the instalaltion files

To install Windows from you freshly prepared drive, you need to copy all the contents of the DVD disc or ISO image to your drive. Do it by selecting all files and copy them to the root of your USB drive.

Now you can go and boot from the USB drive to install Windows.

Diskpart commands list

Here are the commands we used in this tutorial. This list can help you as a quick reference.

DISKPART> diskpart
DISKPART> list disk
DISKPART> select disk X
DISKPART> clean
DISKPART> create partition primary
DISKPART> select partition 1
DISKPART> active
DISKPART> format fs=ntfs quick label="Win8"
DISKPART> assign
DISKPART> exit

Thanks to Ajus for this excellent post