In Windows I have QoS checkbox (selected by default) along with ipv4 etc. What is that? Should I turn it off if I don't need QoS? Does it occupy resources?
closed as not a real question by Zoredache, Wesley, Michael Hampton♦, Lucas Kauffman, Magellan Dec 15 '12 at 23:09
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It's Quality of Service, it prioritizes certain traffic.
As in Windows 2000, programs can take advantage of QoS through the QoS APIs in Windows XP. One hundred percent of the network bandwidth is available to be shared by all programs unless a program specifically requests priority bandwidth. This "reserved" bandwidth is still available to other programs unless the requesting program is sending data. By default, programs can reserve up to an aggregate bandwidth of 20 percent of the underlying link speed on each interface on an end computer. If the program that reserved the bandwidth is not sending sufficient data to use it, the unused part of the reserved bandwidth is available for other data flows on the same host.
There is a tweaking guide here.