That processor has Turbo Boost, and SpeedStep.
It's got a 1.86GHz clock speed.
Turbo Boost will shut down sections of the chip in order to boost the clock speed of some of the cores. This is done when there are a couple/few CPU-intensive threads active, and dynamically. it's so you can get more power for a short time, with the same overall power consumption (basically).
SpeedStep is related to power savings. When the chip is less busy (but not idle) SpeedStep will slow the clock down so that it's consuming less overall power. It ramps back up to the default clock speeds when the system becomes busier. It slows down and speeds up in 3 (or more) "steps", depending on how busy the system is.
I think even the 'default' Windows CPU gadget reflects this, and I know there are other popular ones in the Gadget Gallery that do reflect it for sure (I used one for a long time). And, since SpeedStep is implemented in Ubuntu it works, and also reflects it.
So it sounds like you're Windows 7 is not set to use SpeedStep.
Check your Power Options and ensure it's set to "Balanced" or lower, as "High Performance" will keep the CPU clock at 'full speed' all the time by disabling SpeedStep.
The 'full speed' of CPUs with Turbo Boost is all cores running at the same advertised clock speed (four cores at 1.86GHz in your case).
If you click "Change Plan Settings" to edit the current power plan, then "Change advanced power settings", you can them expand "Processor power management" in the tree and set the Minimum and Maximum Processor states.
The minimum should be like 5%.
Also, ensure SpeedStep in enabled in your BIOS. :)