Windows 10 on ThinkPad T440s

The other day I wanted to install Windows 10 on a Lenovo ThinkPad T440s.
It seemed like a simple task:
  1. Download Windows 10 image from Visual Studio subscription.
  2. Extract installation files to USB stick.
  3. Boot ThinkPad on USB stick.
  4. Install Windows 10.
Not quite.
The installation set is not specially large and fits easily on a medium (8 GiB) USB stick.
But the file "install.wim" is larger than 4 GiB in the latest Windows 10 image. And when a USB usually is formatted with FAT32, it can't hold a file larger than 4 GiB.
My first thought was to format the USB stick with exFAT, but the T440s couldn't boot on the USB stick with the installed BIOS level.

My solution was:

  1. Format the USB stick with FAT32.
  2. Download the RTM image of Windows 10 where the file "install.wim" is smaller than 4 GiB.
  3. Extract installation files to the USB stick.
  4. Boot the ThinkPad on the USB stick.
  5. Install Windows 10 RTM.
  6. Update Windows 10 to current release - with several reboots.
How to install Windows 10 later when RTM is not available on Visual Studio subscription might be a larger challenge in the future.
If I meet that challenge then I will update this post.

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