Microsoft Windows reserves 20% of your available bandwidth for their own purposes like Windows Updates and interrogating your PC
Its not permanent as you can override or change it:
Click Start then Run and type "gpedit.msc" without quotes. This opens the group policy editor.
Then double click and navigate through :
-> Local Computer Policy -> Computer Configuration -> Administrative Templates -> Network -> QOS Packet Scheduler -> Limit Reservable Bandwidth.
Double click on Limit Reservable bandwidth.
If you go to the "explain" tab, you can know more about how this reservable bandwidth functions.
For the faster internet speed, simply ENABLE reservable bandwidth, then set it to ZERO. This will allow the system to reserve nothing, so you will get the extra 20% bandwidth.
I have tried it and it shows some greater speed in internet surfing.
-Credit to hack2007.50webs.com