Windows uses 20% of your internet bandwidth by default! Microsoft reserve 20% of your available bandwidth for their own purposes (for updates and interrogating your machine etc..)

Here’s how to get it back.

Click Start–>Run–>and type gpedit.msc. Hit enter.
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 say it is not configured, but the truth is under the ‘Explain‘ tab:

“By default, the Packet Scheduler limits the system to 20 percent of the bandwidth of a connection, but you can use this setting to override the default.”

So the trick is to ENABLE reservable bandwidth, then set it to ZERO. This will allow the system to reserve nothing, rather than the default 20%. Works on XP Pro and 2000. Enjoy your full speed internet connection.