Installing Windows 7 from USB flash drive

Past few couple of days I had some problems with buying Windows 7 and getting it installed. Long story short: they sold me 32bit OEM Home Premium version and I wanted 64bit version. They refused to replace it since I already opened the package. Let’s not get into details that they shouldn’t even sell me the OEM version and that Microsoft won’t be too happy to hear about this1 but I had a problem and it needed fixing.

Microsoft support was VERY helpful and they told me that I can use my existing serial number to install 64 bit Windows 7 Home Premium OEM, not the retail version, but OEM. Great! Unfortunately they told me to get the installation DVD somewhere else.

Read on if you want to know how I solved my problem …

The trouble was that somewhere else didn’t have the Windows Home Premium 64bit OEM installation medium. All I could find were retails of Ultimate and Enterprise version. I could have looked longer and harder and I’d probably managed to find them.

But I stumbled on a better solution. Windows 7 DVD’s are all the same, there is just this configuration file that tells the installation program what to install. It is called EI.CFG.

It resides in the /sources directory on a DVD and it looks similar to this:2

[EditionID]
Ultimate
[Channel]
Retail
[VL]
0

In this particular example installation program will know that it is installing Windows 7 Ultimate from a Retail package. I needed Home Premium from OEM channel.

Grab 4GB USB flash drive, format it and copy the contents of the Windows installation DVD to the root directory on USB drive. Then edite EI.CFG file to suit your needs. Mine looked like this after editing:

[EditionID]
HomePremium
[Channel]
OEM
[VL]
0

[Update 12/11/2009]:
We were told that the best way to do this is to simply delete this file from USB drive. Installer will then ask which version you want to install and you can simply select it from a drop down menu. You still need to select the correct version otherwise your key will be unusable and you will have to repeat the installation.

After that you will need to make USB drive bootable. Luckily the tools needed for this are on the Windows 7 installation DVD. Open cmd.exe and switch to boot directory on the installation DVD.

c:\> d:
c:\> cd boot

Then you need to run bootsect program and specify the drive letter of your USB key:

bootsect /nt60 e:

In the above example boot sector for Windows Vista (or Windows 7) will be created on drive E:. Now you need to reboot and tell your computer to boot from USB drive.

Windows 7 installation should start and you will be installing the version that you specified in the EI.CFG file.

Keep in mind that your serial number determines which version of Windows you can install. If you have serial number that belongs to Retail package you won’t be able to install OEM version with it and if you have serial number for Home Premium, you won’t be able to install Ultimate version.

The whole procedure in four short steps:

  • Format 4GB usb drive
  • Copy contents of Windows DVD to USB drive
  • Edit \sources\ei.cfg if necessary or even better, delete this file from USB drive
  • Make USB drive bootable with bootsect /nt60 e:

Many thanks to OmegaBlue for all the tips and PaJo for the update. :)

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Footnotes:
  1. Yes, they will hear about it … []
  2. It will depend on which version of Windows you have []