Why do laptops need fans but tablets don't?
Solution 1:
Tablets don't need fans because their CPUs (processors) have a different architecture that is more power efficient and doesn't generate as much waste heat. This is also why they are able to get 10 hours of run-time on a relatively small battery.
The other side of this, though, is that the tablet processor is no where near as powerful as a laptop processor, even cheap netbooks. This is why, for example, nearly all tablet operating systems absolutely prevent you from running more than one app at a time, or two at most, and strictly limit what kinds of tasks apps are able to do in the background.
We are seeing some rapid convergence, though... tablet processors are closing the performance gap with each generation, and chip designers are also working to make laptop/desktop processors more and more power efficient.
Solution 2:
There are three heat generation points in a laptop:
- Processor
- Chipset
- Graphics
- Power regulators
1-3 of the above subsystems work at very high speeds. Because these subsystems are clocked so high, the power requirement is very high. High speed and hi power requirements generate a lot of heat in Si. Also, these subsystems use PCIe to communicate and PCIe needs to be clocked to a certain frequency to operate. Multiple PCIe lanes originate from the chipset therefore increasing the power usage and generating heat.
Tablets don't use high end processors or graphic subsystems. Most of them use ARM core that was developed for embedded market. Such processors don't use special chipsets or PCIe bus and are not clocked at high speeds as the laptop processors. Hence they don't generate as much heat.