What is the "u" in the latest Windows 7 ISO file name?

[scottw182]

I downloaded the latest Windows 7 ISOs yesterday and noticed they all have a "u" in them, the previous ISOs I had did not. Example:

en_windows_7_ultimate_with_sp1_x64_dvd_618240.iso
en_windows_7_ultimate_with_sp1_x64_dvd_u_677332.iso

I'm kind of OCD about my files, so I need to know what this is, and make sure I have the correct version.

 

[scottw182]

bump

 

[TerryFawkes]

The "u" represents Windows 7 SP1-U Media Refresh. This page explains it further.