In response to original thread: http://forum.techinferno.com/hwinfo32-64-discussion/65-alienware-fan-control-83.html#post39152
Let me start from beginning and since you seem to have technical background, I can go into details
I suppose the IT8518E is just one of several dozens of different Embedded Controllers (EC). Which EC chip is used on a particular system doesn't matter much in terms of fan control. The important thing is the program that this EC runs (firmware). It's a proprietary piece of system and is usually developed by ODMs. So even in case of DELL, this part can be designed by Quanta, Compal, etc.. They design the core and add DELL-specific requirements. Now we come to the point - usually parts developed by a particular ODM (including EC firmware) follow their own internal design and thus work similar for several platforms. So for example you can have a Toshiba notebook and an Alienware/DELL notebook which both were designed by the same ODM (e.g. Compal). The point is that on both of them you can control the fans using the same method
This means esentially, that the Host-EC interface and EC RAM layout (which you check/modify in RW-Everything) is very similar.
Now, every notebook/model is designed using different concepts from different ODMs. This means that there's no universal method to control all such systems.. It's very hard to determine particular implementation and EC registers and their meaning.
Now let's go a bit back. The ODM (e.g. Compal) designs a board for an OEM (e.g. DELL). But DELL has its own requirements and adds something to that design. DELLDIAG - their own system for diagnosing, monitoring and controlling the computer. So DELLDIAG has an uniform top interface to the host (proprietary) and on the bottom interfaces with ODMs implementation including the EC (and fan control).
So for most DELL machines it's possible to access/control proprietary components using an uniform interface.
Now the answer to your question - on your notebook, HWiNFO doesn't access the EC directly, but uses the DELLDIAG interface instead. AFAIK, this interface is nowhere in public documented, you can find some details in the i8kfangui sources if you wish. This interface uses software-triggered SMIs to execute the SMM-handler which then transforms the requests to particular system/EC implementation.
Fan control in DELLDIAG also doesn't work directly with fan RPM speeds, but levels instead. So when HWiNFO sets a particular fan speed, it tells the system which level to set. The interface also allows to ask what RPM belongs to a particular fan level. So when you set a certain speed and it doesn't reflect it, then it's probably a fault in the firmware and I can't do much about that.
I hope this helps to understand the situation a bit more