(PAID) INCREASE YOUR INTERNET SPEED BY 25% WITHOUT ANY SOFTWARE!

The idea that Windows reserves 20% of bandwidth is a myth that has been known for a long time. But like many performance myths it continues to spread.

In reality 100% of bandwidth is available to user programs. By default a portion of bandwidth (20% by default) CAN be reserved if a QOS aware application requests it. But even then nothing is reserved unless the application is actively using it's bandwidth.

Incidentally Windows Update does not use QOS. It uses a service that operates at a lower priority than regular programs so it's impact on bandwidth should be minimal, even when it is operating.

This misguided "tweak" effectively disables QOS. The problem is that if you are using a QOS aware application it may not be able to operate properly.

I advise everyone against doing these modifications to the Group Policy Editor.