he Windows 7 downloaded image that many online software retailers supply is simple too large to install from a single CD, being about 2.2Gb This short guide has step-by-step instructions on how to install Windows 7 from any USB device with more than 2.3Gb free space.

You will obviously need an original Windows 7 DVD or image file. If using an image file it will need to be mounted on a virtual drive so you can access the files inside.

There are many free tools available for this, but I use Daemon Tools. You will also need a Vista or Windows 7 PC as Windows XP doesn’t have the diskpart or bootsect tools.

I just downloaded Windows 7 and wanted to install it on a notebook. There were two main problems with this:

  1. The downloaded Windows 7 disc image was 2.23Gb
  2. The notebook I intended to install windows 7 on doesn’t have a disc dirve!

Creating the Bootable USB

Plug in the USB flash drive, then open an elevated command prompt (Start-> All Programs-> Accessories-> right click "Command Prompt" and select "Run as…"). First, find out which disk number Windows has assigned to the drive:

Batch cmd 
diskpart
list disk

You should be able to see what the USB drive is by the size listed as capacity – it's usually disk 1, but double-check before continuing!

Everything below assumes it's disk 1; swap in the correct number if yours differs. This next set of commands wipes and reformats the drive, so make sure you've picked the right one:

Batch cmd 
select disk 1
clean
create partition primary
select partition 1
active
format fs=NTFS
assign
exit
Double-Check the Disk Number The clean command wipes the selected disk entirely. Confirm you've selected the USB drive and not an internal one before running it.

At this point the USB drive is formatted and ready, but it still isn't bootable.

Making It Bootable

Every Vista and Windows 7 disc ships with a tool called bootsect that handles this part. In the same terminal window, switch to the disc (or mounted image) drive, assuming it's drive E: and move into its boot folder:

Batch cmd 
e:
cd e:\boot

Then, assuming the USB drive is G:, run:

Batch cmd 
bootsect /nt60 g:

Swap in whatever drive letters actually apply to your disc and USB drive. Once that's done, the USB is bootable and the command prompt can be closed.

Copying the Files

Last step: copy every file from the Windows 7 disc (or mounted image) across to the USB drive. Once that finishes copying, set the machine's BIOS to boot from USB, and it'll install from the flash drive exactly like it would from a DVD.