Microsoft reserves 20% of your available bandwidth for their own purposes like Windows Updates and interrogating your PC etc
You can get it back:
Click Start then Run and type "gpedit.msc" without quotes. This opens the group policy editor. Then go to:
--> Local Computer Policy
--> Computer Configuration
--> Administrative Templates --> Network --> QOS Packet Scheduler --> Limit Reservable Bandwidth.
Double click on Limit Reservable bandwidth. It will...