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Geek Culture / Why dont tablet computers get hot and need cooling fans?

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Dark Java Dude 64
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Posted: 11th Jan 2012 07:06
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Right now I am typing on my iPad, and I was wondering, why dont tablet computers get warm? I know the the iPad has about half the processing power my laptop does, but it has insanely more powerful graphics than my laptop does, and even when playing high quality 3D games for a long time, the iPad doesn't even get noticeably warmer. Why is this?

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FireIndy
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Posted: 11th Jan 2012 07:19
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My guess is that the hardware consumes little power. I also believe the iPad has no moving parts, which produces less heat. And that it also has a larger surface area to disperse the heat.


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The Zoq2
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Posted: 11th Jan 2012 08:39
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I have been wondering this to... Why do I have burnmarks on my table.from my laptop with a 2.2 ghz dualcore when my android with 1.4 ghz dualcore dosn't evenget warmer?
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Benjamin
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Posted: 11th Jan 2012 08:45
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Some hardware is designed to use little power (useful in handheld devices, especially tablet computers) and as a result won't generate as much heat.

At least that's my take on it.



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Dark Java Dude 64
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Posted: 11th Jan 2012 09:01
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But i though power usually correlated to speed, cores, bits, etc. Also, if they design these tablets and smartphones to use little power, then why doesnt it seem that they do that for a regular laptop?

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Quel
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Posted: 11th Jan 2012 09:20
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Because it's god damn expensive, that's why.

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Benjamin
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Posted: 11th Jan 2012 09:21
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Quote: "Because it's god damn expensive, that's why."


This. Powerful, cool, energy-efficient components are expensive.



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Dark Java Dude 64
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Posted: 11th Jan 2012 09:59
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Interesting but the A5 chip is only 14 bucks whereas a slightly better Intel or AMD is rockin' up there in the 6o dollar range!

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Indicium
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Posted: 11th Jan 2012 11:51
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I thought the processors on smaller devices used a different architecture to desktop/laptops which produced less heat?

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bitJericho
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Posted: 11th Jan 2012 11:59
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RISC processors use less power. Combine that with the lower clock speed and top-of-the-line manufacturing process, they produce very little heat.

To be fair, we'd probably all be on ARM processors today except they aren't exactly backwards compatible with x86. However, with products like gcc and llvm, it's very likely that windows 8 will launch an ARM processor craze, which will be a welcome change.


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TheComet
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Posted: 11th Jan 2012 13:29
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Quote: "RISC processors use less power."


What does the instruction set have to do with power consumption?


Mobile phone processors and microcontrollers in general consume much less power than desktop computers. This is achieved by using low voltage CMOSFETs (they are able to operate at around 1 V), and lower frequencies. The power dissipation of a CPU can be roughly calculated with this formula:

P = C * U^2 * f

P = Power [W]
C = Gate Capacitance [F]
U = Voltage [V]
f = frequency [Hz]

Let's take an AMD Phenom X6 1090T as an example:

U = 1.2 V
f = 4.2 GHz
C = Unknown, considering the architecture most likely around 15-20 nF

P = 120 W - Wow, where is my stick and sausage?

So now let's take a mobile device, specifically the A5 processor:

U = 1 V
f = 800 MHz
C = Unknown, most likely around 2-5 nF

P = 4W - Guess I'll be eating cold tonight...

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bitJericho
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Posted: 11th Jan 2012 13:56
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Quote: "What does the instruction set have to do with power consumption?"


RISC processors don't require as much stuff on the die. RISC processors are more efficient by design as well.


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David R
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Posted: 11th Jan 2012 14:05 Edited at: 11th Jan 2012 14:10
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Quote: "What does the instruction set have to do with power consumption?"


Fewer and less complicated instructions means less work needs to be done to decode them, and hence less power is consumed in doing so

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TheComet
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Posted: 11th Jan 2012 14:13
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I can't see why that would work... The RISC instruction set does have a more narrow range of instructions, but in the end the transistors in the CPU are going to switch just as many times to process an integer as an x86 CPU would. Or is that incorrect?

Even if I were incorrect assuming so, the formula above isn't influenced by that. The CPU may be able to process instructions more "efficiently", but that only indrectly causes less power dissipation. Ultimately the factors are frequency, voltage, and capacitance of the transistors.

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MrValentine
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Posted: 11th Jan 2012 20:15
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http://www.bbc.co.uk/news/technology-16492156

Joy of joys for us x86 lovers (and well x64 too as we can get win 8 on mobile platforms natively soon... )

just thought I would mention this as nobody has mentioned it yet...

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