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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?

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Not all laptops need fans. Modern, low-power laptops like Samsung chromebooks don't. "At just over 2.4 pounds, 0.7 inches thin, and with over 6.5 hours of battery life, the Chromebook can go anywhere you go. It's built to stay cool, so it doesn't need a fan and runs silently (no humming, unless you’re playing music)." Chromebook –  David Schwartz Jan 22 '13 at 20:52
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@DavidSchwartz: It's important to note, I think, that the current generation Samsung Chromebook runs on ARM architecture. On a hardware level it's much closer to a tablet than a laptop. –  Phoshi Jan 22 '13 at 22:18
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@Phoshi: Absolutely. They're very different designs through and through. The form factor isn't what makes the difference but the choice of all the other components -- mass storage, the CPU, the GPU, the RAM, the backlight, and so on. –  David Schwartz Jan 22 '13 at 22:20
    
Consider also the nightmare that it would be to have a rapidly moving, very flimsy mechanical part in a device in almost constant motion. Mechanical parts are risky enough in laptops as it is. –  Ben Brocka Jan 24 '13 at 13:26
    
The Surface Pro has fans in it... Then again, the Surface Pro is just a laptop stuffed into a tablet form factor to begin with (which I think is awesome IMHO). –  Breakthrough Feb 21 '13 at 22:20

5 Answers 5

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.

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I can install Quasar on my jailbroken iPad 2, and it doesn't slow down significantly. But my gran's netbook (3 years old) takes for ever to start Chrome, nevermind running 2 things at once. Is it because desktop OS have been around for ages on many different systems and become "bloated", whereas Android, WP, and iOS are more made for the latest chips? –  Jonathan. Jan 22 '13 at 19:28
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The netbook is slow because it's loading from a rotating hard disk... and likely a slow 5400rpm one at that, whereas the iPad loads from flash memory. Also, there is quite a bit more going in the background... but mainly its the disk. –  Joel Coehoorn Jan 22 '13 at 19:32
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@JoelCoehoorn: It's a lot more than that. An ultraportable with an SSD still isn't going to be fast, and a netbook that's running everything in-memory is still sluggish--just less so. The netbook is slow because it was built for the absolute minimum price it could be. Every component is subpar, not just the drive. –  Phoshi Jan 22 '13 at 22:20
    
@Karan There've been fan sporting windows/pen tablets for over a decade. Somewhere in my clutter I've got one with a 12(?) inch screen, about an inch thick, that was good for 5-6 hours/charge with XP and a ULV p3-900ish processor. For ~$140 it made a usable ereader when an early kindle was $300+. I never used it for much else, XP's hand writing recognition needed better penmanship than mine; and while W7 could handle my scrawl it idled at 5% load, enough that the chip never made the lowest power state and battery life collapsed to ~3 hours. –  Dan Neely Jan 23 '13 at 2:11
    
@DanNeely that sounds like a superuser question in the making... what could you turn off in Windows 7 to get the load on that old machine low enough to make it serviceable again, or, alternatively, what could you do to improve the default hand-writing recognition in XP (though with XP going EOL in about a year, the former should be strongly preferred). –  Joel Coehoorn Jan 23 '13 at 2:14

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.

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I would have thought having a SSD drive vs. a rotating HD would also help reducing heat generation (not to the same extent as the CPU/GPU parts which are the hottest in the box). –  assylias Jan 23 '13 at 19:14
    
@assylias True, they also play a part in heat generation. You are right, friction in the hard drives also generates heats. Heat generated is directly proportional to the drive RPM. –  Chetan Bhargava Jan 23 '13 at 19:17

Its a matter of design and requirements. Arm processors are really power efficient, but don't have performance to the same level as an x86 in many cases.

For a low power, passively cooked heatsinkless x86, take a look at via's designs, the old AMD geodes or the phone-grade atom processors intel is working on.) TArm processors also run at slower speeds (the fastest phone processors run at about 1.2 ghz I believe with up to 4 cores, with the slowest modern X86 processor at twice that), though thats an apple and oranges comparison - clock speed dosen't compare between processor families (the PIV was outclassed, rather embarassingly by pentium Ms of the era, at half the clockspeed).

Other components may be less powerful as well - phones wouldn't need to handle many storage devices (the early desktop grade atoms had a passively cooled main processor, and a fan for the chipset) so they can be less complex and produce less heat.

Basically each has a different set of compromises (which gradually converge - PCs are becoming more SOClike, while Phones are becoming pocket computing devices, with more complex processors powering them.), Power vs Power efficiency, and complexity and flexibility vs simplicity for a monolithic design.

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Older laptops have older processors, which are made with a less advanced, bigger architecture process. Means the transistors are bigger, and generate more heat.

As processors architecture get smaller, they can fit more and more transistors in the same area, since the transistors are smaller themselves.

Right, so tablets and phones, TV's use ARM processors, which is an architecture, just like x86, x64, but designed by another company, made to produce almost no heat waste. And to be energy efficient. This is likely accomplished, because there are less transistors fit tightly, close togther.

ARM is different than most desktop processors, as they have less transistors on the same area.

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Basically the race is not so much on speed anymore as on saving power. This is why we have moved on to SSD drives, low powered ARM CPU's and smaller form factors. Why do laptops generally require more cooling, because they do more, they can run multiple programs, and have a robust OS that also does more. Tablets and smartphones generally run one app at a time and this prevents the hardware from running too hot. All mobile processors have been designed for their mobile purpose. Many say Apple using mobile chips in the iMac desktops actually degrades performance over the traditional desktop CPU of the same speed. I tend to agree, but Apple must use mobile processors because of the form factor in the iMac's and even Mac Mini. This is really not such a problem anymore and like the Chromebook and tablets which can do HD video and high resolutions without much issue. Its because the focus recently in technology of processors has been on mobile ones. Let's also remember the real reason heat is created is from current draw. As processors in generally started requiring less voltage, they also have become cooler. Unless your a gamer almost any system and processor today with do web without a problem. Its only those applications like video and photo editing or CAD drawing will you need more processing power.

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