Intel Hyper Threading technology allows 1 processing core to run 2 threads simultaneously alternating between the two. This is why you get 2x number of threads per core number on processors.
Typically, windows task manager shows the number of threads. So, in your case you're seeing 4, in my case, since I got a quad core processor and thus it can run 8 threads at the same time, task manager shows 8 bars for me.
As a comparrison, AMD processors will have 1x thread per core, so you will see 4 threads on 4 core CPU.
Where exactly are the bars you mention on task manager? I have a quad core but only see four ...that is if we are looking at the same thing.