Quote from ukhardy07 on TBB
BT speedtester is multi threaded. I believe it uses 9 threads but could be wrong.
Let me use a basic analogy to explain this to you. Lets say I have 10Mbps bandwidth between 2 houses.
House 1 downloads a file. House 2 downloads a file. Both houses get 5Mbps each.
Now, instead, house 1 downloads a file with 9 threads. House 2 downloads a file with 1 thread.
House 1 now gets 9Mbps, House 2 gets 1Mbps.
See how multi-threaded downloads mask congestion...