You can install the Windows 8 Consumer Preview on a USB flash drive and run it from there.
The performance of the system when booted from an USB attached device depends on the performance of USB port.

This post gives step-by-step instruction on how to setup Windows 8 Consumer Preview on a USB drive.

Before we start

What we need:

Since we are going to do low level system stuff you should make sure that you have a current backup of the PC you are working on.

Preparing the USB drive

  • Connect the USB device to your PC
  • Open cmd.exe in administrator mode
  • Create the boot partition on the USB drive:
    • Go to folder c:\windows\system32
    • Run diskpart
    • Get the USB drive’s disk number: list disk
    • Select the USB drive as active drive: select disk <disk number>
    • Purge existing partions from the drive: clean
    • Create a new primary partition: create partition primary
    • Quick-format as bootable NTFS: format fs=ntfs quick
    • Set partition as active: active
    • Close diskpart: exit

Extract the image file for Windows 8 Consumer Preview from the ISO file

  • Mount the ISO file

    If you are running Windows 8 you can mount it as virtual disk.

    On Windows 7 you need the help of a third-party utility like MagicISO or you could burn the ISO on a disk.

  • Copy the image file

    The image file image.wim can be found in the sources folder of the ISO image.

    Create a new folder on your local hard drive (e.g. c:\ win8onusb) and copy the image.wim file to that folder.

Installing the image on the USB drive

  • Install the AIK

  • Get imagex.exe from the AIK

    In C:\Program Files\Windows AIK\Tools you find three versions. Select the one that matches the architecture of the Windows image you plan to install.

    E.g. when you want to install a 32-bit Windows 8 version get the version from x86 folder.

    Copy imagex.exe to the folder (e.g. c:\win8onusb) which already has the image.wim file.

  • Install the image

    Check which drive letter is assigned to the USB drive (e.g. g:).

    On the command prompt cd to the folder containing the image.wim file (e.g. c:\win8onusb)

    Run the following command to install the image:

    imagex.exe /apply install.wim 1 g:\ (replace g with the drive letter of your USB drive)

    This will take some time…

  • Add the boot record

    At the command prompt enter:

    bcdboot.exe g:\windows /s g: (replace g with the drive letter of your USB drive)

That’s it.

First boot

  • Make sure that your PC’s BIOS is setup to boot from USB.

    In addition you might have to tweak the order of the hard disks listed in the BIOS, if the USB device is listed there.
  • During the first startup the PC hardware will be detected.

    This might take some time. It will then reboot and present the screen requesting the product key.