# How do smartphone CPU's work without a fan? **URL:** \ **Category:** Factual Questions\ **Created:** [June 15, 2013, 4:06am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045 "2013-06-15T04:06:24Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Quintas](https://avatars.discourse-cdn.com/v4/letter/q/48db29/32.png) [@Quintas](https://boards.straightdope.com/u/Quintas)\ **Post date:** [June 15, 2013, 4:06am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/1 "2013-06-15T04:06:24Z")
My phone has a quad core 1.5 ghz processor. How does the thing not melt? A 1.5 ghz laptop or desktop needs a fan in addition to a heatsink. How have they gotten around this on mobile chips? A secondary question. What would be the drawbacks if a laptop or desktop was built using a mobile CPU? And why aren’t they if they need no fan and are therefore quieter? ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [June 15, 2013, 4:55am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/2 "2013-06-15T04:55:56Z")
Smartphones use special processors (usually ARM-based) that are designed primarily for energy efficiency and low heat production. They also omit many features that are necessary for desktop and laptop cpu’s but irrelevant for smartphones like the pci/sata/expansion bus, external memory bus (most smartphones have the memory and graphics processor built right on top of the CPU), and the like. ---
**Author:** ![Amblydoper](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@Amblydoper](https://boards.straightdope.com/u/Amblydoper)\ **Post date:** [June 15, 2013, 5:20am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/3 "2013-06-15T05:20:12Z")
Well, in simple terms, the chip in your phone is designed to run off small, low power batteries that fit in your pocket. Every year engineers build chips with smaller transistors that need less electricity to operate then older, larger designs. Mobile chips are designed to use less power and put out less heat. We can not compare clock speeds of a mobile chip to clock speeds of desktop chip. A laptop or desktop chip will do much more work at 1.5 ghz than a mobile cpu will do at the same speed. To do so, it uses a lot more power and outputs a lot more heat. Today’s mobile chips can sort of match the performance of desktop chips from 10 years ago (however, they are designed for very different tasks, and direct comparisons are not accurate). Those older chips were much bigger, used way more power, and put out way more heat. Modern chip design is smaller and more efficient, even on desktop machines. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 15, 2013, 6:28am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/4 "2013-06-15T06:28:31Z")
No not smaller. Each gate - as with each transistor, each capacitor - is smaller. BUT Modern cpu’s have grown larger - more area - why ? - take more power - why ? - MORE CORES - MORE CPU LEVEL CACHE - WIDER BUSES - - HAVAARD vs Van Neuman Memory - MORE EXECUTION UNITS - MORE PIPELINE STAGES and requisite coordination logic (eg detecting the requirement to stall the pipeline) There are two specs therefore. The PDA/phone has only a single core ? And the average cycles per instructions. Moderm pentiums are doing TWO instructions per cycle. (deep pipelining). Your PDA may be taking 8 cycles to do one instruction. and only providing one core. About the same GHz… so ?? massive difference in transistor count. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 15, 2013, 6:31am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/5 "2013-06-15T06:31:52Z")
Also intel’s are CISC and there’s an overhead of extra transistors for this drawback of history. ( IBM using 8086 cpu before CISC was invented.) PDA and phone use the strongARM or equiv, a RISC, which allows a power saving. ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [June 15, 2013, 1:52pm UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/6 "2013-06-15T13:52:55Z")
> [@Isilder](#): > > There are two specs therefore. > The PDA/phone has only a single core ? Mid to high tier phones these day are dual core. And that’s often just for the application code. Sometimes there are more (possibly less powerful) cores for other functions in the same IC. Other than that, I agree with most of what’s being said here. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 15, 2013, 2:35pm UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/7 "2013-06-15T14:35:43Z")
> [@Quintas](#): > > My phone has a quad core 1.5 ghz processor. How does the thing not melt? A 1.5 ghz laptop or desktop needs a fan in addition to a heatsink. How have they gotten around this on mobile chips? your phone has a relatively small, simple ARM SoC (system-on-chip.) A desktop/laptop has a relatively complicated CPU with many times more transistors. An IC’s power dissipation roughly scales with the #of transistors switching, the frequency of the switching, and if I remember correctly the square of the supply voltage. put simply, your phone’s CPU is a tiny little thing that dissipates maybe one watt of power. Your desktop’s CPU is a much bigger thing that can dissipate up to 100 watts of power. > [@](#): > > A secondary question. What would be the drawbacks if a laptop or desktop was built using a mobile CPU? And why aren’t they if they need no fan and are therefore quieter? it would be very slow. Even though your phone’s ARM CPU is running at a similar clock speed, it’s still a relatively simple processor compared to a beast like a Core i5. The ARM CPU can’t do as much per clock cycle as the Core can. If you want to get an idea of what running a desktop OS on a mobile CPU would be like, try Windows 7 on an older Atom netbook. Anything using Flash or video will bring it to its knees. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [June 15, 2013, 2:39pm UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/8 "2013-06-15T14:39:51Z")
> [@Quintas](#): > > A secondary question. What would be the drawbacks if a laptop or desktop was built using a mobile CPU? And why aren’t they if they need no fan and are therefore quieter? They do. For example, search for Minix Neo X5. They’re not powerful enough to run Windows, though. Most run Android. ---
**Author:** ![Baron\_Greenback](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/baron_greenback/32/48_2.png) [@Baron\_Greenback](https://boards.straightdope.com/u/Baron_Greenback)\ **Post date:** [June 15, 2013, 3:01pm UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/9 "2013-06-15T15:01:25Z")
> [@Isilder](#): > > The PDA/phone has only a single core ? Quad-cores are the norm at the high end now. My One X has an Nvidia Tegra 3 quad-core, which also has a companion core for use when the phone isn’t doing very much. ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [June 15, 2013, 3:42pm UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/10 "2013-06-15T15:42:07Z")
There are fan-less processors which are designed for more more robust operation, including displaying 3D graphics. [This processor](http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=48197), which is for example, is optimized for digital signage, a challenging requirement. > [@](#): > > The AMD Embedded G-Series processor is the world’s first integrated circuit to combine a low-power CPU and a discrete-level GPU into a single embedded Accelerated Processing Unit (APU). This unprecedented level of graphics integration builds a new foundation for high performance multi-media content delivery in a small form factor and power efficient platform for a broad range of embedded designs. Based on a power-optimized core, the AMD Embedded G-Series platform delivers levels of performance in a compact BGA package that is ideal for low power designs in embedded applications such as Digital Signage, x86 Set-Top Box (xSTB), IP-TV, Thin Client, Information Kiosk, Point-of-Sale, Casino Gaming, Media Servers, and Industrial Control Systems. In my limited experience, boards which based on these chips are optimized for signage players or controllers. I was only concerned about the quality of the video playback so I didn’t particularly attempt to make close comparisons to the processors used in note books. Signage players are optimized for video playback and are often not based on Windows platforms, which saves on processing overhead. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 16, 2013, 3:18am UTC](https://boards.straightdope.com/t/how-do-smartphone-cpus-work-without-a-fan/661045/11 "2013-06-16T03:18:10Z")
> [@Quintas](#): > > A secondary question. What would be the drawbacks if a laptop or desktop was built using a mobile CPU? Such laptops do exist. The main drawback is that they can’t run Windows or OS X. See for example the [Google Chromebook](http://www.engadget.com/2012/11/07/samsung-chromebook-review-2012/).