These are squirrel cage fans. They work in a differant way than normal fans and generally are much quieter, and have more airflow. In fact, the majority of the fans that power central air systems (heating and air conditioning) that I've seen are this type of fan (of course much bigger). The main disadvatage is that they tend to be larger because of the style of the fan. This means that they are not very popular for usage in computers, and usuallly require special or home made brackets to use. But if you are a modder who wants more air flow, and quieter fans for things like your case, they can be great if you have room.