A bottleneck is a phenomenon by which the performance of an entire system is severely limited by a single component.
This is quite true in case of Windows XP Pro-based computer. It has a something called Quality of Service. Technically, it is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. Such a mechanism implies that the bandwidth is not completely optimized, and hence is not used in its maximum.
Turning the QoS Scheduler off can help increase the available bandwidth by leaps and bounds. It is a simple task, as outlined in the steps below (remember that it is XP Professional only):
1. Go to Start > Run, type gpedit.msc and hit enter.
2. In the window that comes up, in the left pane, double click Administrative templates, then Network and then QoS Packet Scheduler (see image below).
3. In the right pane, double-click Limit Reservable bandwidth.
4. In the window that comes up, click ‘Enabled’, and then set the ‘Bandwidth limit’ to 0%.
5. Click OK, restart the computer and you’re ready to go!