Windows allots 20 per cent of the bandwidth by default for various services
like Windows update and spyware checks. The trick is fairly simple to get
hold of the unused bandwidth. Here's what you do Go to
Start> Run and type ---gpedit.msc.
Go to Administrative templates
Networks > QoS Packet Scheduler.
Click on Limit Reservable Bandwidth and check the enabled box
and then change the Bandwidth limit from 20% to 0 %.
The screen shots above are the before and after results.