An hour after you've settled in with your tablet, busy playing a game, it's still quiet as a mouse but most laptops would be serenading you with the whir of a system fan. Why can tablets forgo a cooling fan?

Today's Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

SuperUser reader Jonathan is curious about the hardware differences between tablets and laptops. He writes:

I'm curious why a tablet doesn't need fans but all laptops do, even the cheap and less powerful netbooks. I thought at first it would be that the screen on a tablet is smaller than a laptop, so the graphics chip doesn't have to be as powerful and so doesn't generate as much heat. But then the new iPads have retina display which have a much bigger resolution than most laptops.

Then I thought maybe it's because tablets don't multitask like laptops can, but some Android tablets can have 2 (at least) apps open at once, and even jailbroken iPads can. While some low end netbooks struggle to run a web browser and word processor.

If you attach a keyboard to tablet you have a laptop, so why do laptops seem to generate disproportionate amounts of heat?

Is the difference between ARM and Intel/AMD chips? If so what is it about the different chip designs that make Intel/AMD produce so much more heat than ARM chips?

Let's dig in and see what everyone has to say about the hardware divide between the two.

The Answer

SuperUser contributor Joel Coehoorn offers this description of the divide:

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, 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.

Chetan Bhargava highlights some additional hardware factors that contribute to the heat:

There are three heat generation points in a laptop:

1. Processor
2. Chipset
3. Graphics
4. 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.

Finally, it's worth noting that not all laptops have cooling fans many of the current generation Ultrabooks have an super small form factor, lower power-parts (like SSDs) and use heat dissipation tricks that don't rely on fans.

Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

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