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>> On an energy/computation basis they make more sense than x86 processors right now. Does anyone have ANY numbers that back this up? I've heard this refrain m

by iyulaev 14y ago

>> On an energy/computation basis they make more sense than x86 processors right now. Does anyone have ANY numbers that back this up? I've heard this refrain many many times but I've never seen any hard numbers to prove this. On a processor-per-processor basis sure an ARM SoC beats a Intel Xeon. But flop or dhrystone, x86s destroy ARM processors. In a virtualized world, where the number of real systems doesn't have to match the number of servers, x86 still appears to hold the lead.

cmccabe 14y ago
ARM cores tend to be more power efficient for three main reasons: they operate at a lower clock frequency, they don't have the CISC legacy baggage, and the low-level software guys have spent a lot more time on power management than on x86. It has to do with the evolutionary heritage of both systems. Most x86 systems are still sold to individuals or small businesses that will plug them into the wall and forget about power dissipation. A typical x86 desktop machine will draw between 300-500 watts. ARM evolved more for the cell phone and tablet market, and typical power consumption for one of those systems would be under 5 watts.
- jrabone 14y ago
  A typical x86 desktop machine will draw between 300-500 watts. With a beefy GPU, perhaps. The new i3 3220T CPU is only 30W MAX TDP, flat out - a typical (ie. non-gamer) rig is looking more like 150W max, and a lot less idle (20W should be possible). Not 5W, but nowhere near 500W.
  - zanny 14y ago
    Yea, that metric seems bizarre. It is worth mentioning though that the lowest TDP chips Intel is selling are 17w mobile ones, comparing a desktop to a mobile chip seems apples and oranges. You also need to consider that Intel is at least a fab tech ahead of ARM chips. I have a Tegra 3 Transformer tablet and that chip was yielded at 40nm, 2 generations behind Intels 22nm, and it has a TDP of 15 watts. Of course under load it would run higher than that, but so would an Intel chip.
  - cmccabe 14y ago
    20W, 200W, what's the difference? Either way, you can't get that out of the battery on a mobile device. And consumers don't generally buy PCs based on power dissipation. Sad, but true. And if you think your typical beige-box PC can handle a power supply that is specc'ed for 150W-- go ahead and put one of those in there. I DARE you.
    - jrabone 14y ago
      The lower figure of 20W is pretty standard: go take a look at the battery in your laptop. Most Dells are 65Whr batteries - ie. 20W for 3 hours of battery life (to a first approximation, LiIon is a bit more complicated than that). The ubiquitous small form factor PCs like the Optiplex 780 (http://www.dell.com/downloads/global/corporate/environ/comply/optix_780_dccy.pdf http://www.dell.com/downloads/global/corporate/environ/compl...) use a 235W (max) power supply, which will be overspecced to trade off failure rates for manufacturing cost. Those machines actually draw less than 150W flat out. And they're everywhere. A certain large e-tailer with an emphasis on frugality used to use them as developer desktops(!). Who knows what's in a typical consumer beige box, but it isn't pulling 500W continuously, unless they're playing, say, Skyrim 24/7 with a big graphics card - in which case of course one would specify the correct (safe) component for the design. I'd argue that they're not typical by that point; most people won't spend £300 on a graphics card (I do).
      - cmccabe 14y ago
        So to recap: * You point a to 235W power supply as an example of the bare minimum PC power supply-- not too far from my 300W round number. * You point out that a power supply rated for X isn't drawing X continuously-- a true statement, but it's responding to an argument nobody made. You have to pick a power supply which is rated for your max load-- everyone knows that, or should. It still doesn't change the fact that both max load and average load for X86 are orders of magnitude greater than for most ARM devices.
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- baq 14y ago
  500 watts is a seriously overclocked with a sli/crossfire gfx setup or the super-high-end offerings like dual gpu on a single card. it's probably less than 1% of all desktop pcs. my ageing desktop with an e8400 and an radeon 4850 draws 270 watts at full load, including display - number straight from the ups.
- Tsagadai 14y ago
  What CISC legacy baggage? Most of the old and underused operations are emulated with microcode on modern x86 processors. Chip makers use profiling tools just like software makers, optimize the most common cases and your benchmarks improve. There are decades worth of engineering optimizations in Intel and AMD's chips. Intel has a massive engineering and R&D budget and competing with that is pretty damn hard. It has nothing to do with evolutionary heritage and more to do with you repeating ancient myths that haven't been remotely close to the truth of a decade.
  - cmccabe 14y ago
    One example of legacy baggage is the fact that x86 doesn't reorder loads and stores as freely as ARM. It would be better for optimization, but it would break the creaky old software that is the lifeblood of the platform. Another example of "evoluationary heritage" is the fact that x86 chips require a northbridge and/or southbridge, whereas with ARM chips, everything is integrated on the chip. This was one reason why Atom-based designs often weren't that low power-- the CPU itself might be low-power, but the glue logic was thirsty. There is evidence that Intel is trying to change this, and put everything on one chip. I'm not trying to say that x86 will never succeed in mobile. I don't have a crystal ball. I'm just saying that the burden of proof is on Intel to prove that it can be cost and performance-competitive in that space. And I am not the only skeptic-- Apple and Microsoft use ARM for most of their mobile offerings.
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by iyulaev 14y ago

cmccabe 14y ago

ARM cores tend to be more power efficient for three main reasons: they operate at a lower clock frequency, they don't have the CISC legacy baggage, and the low-level software guys have spent a lot more time on power management than on x86. It has to do with the evolutionary heritage of both systems. Most x86 systems are still sold to individuals or small businesses that will plug them into the wall and forget about power dissipation. A typical x86 desktop machine will draw between 300-500 watts. ARM evolved more for the cell phone and tablet market, and typical power consumption for one of those systems would be under 5 watts.

jrabone 14y ago
A typical x86 desktop machine will draw between 300-500 watts. With a beefy GPU, perhaps. The new i3 3220T CPU is only 30W MAX TDP, flat out - a typical (ie. non-gamer) rig is looking more like 150W max, and a lot less idle (20W should be possible). Not 5W, but nowhere near 500W.
- zanny 14y ago
  Yea, that metric seems bizarre. It is worth mentioning though that the lowest TDP chips Intel is selling are 17w mobile ones, comparing a desktop to a mobile chip seems apples and oranges. You also need to consider that Intel is at least a fab tech ahead of ARM chips. I have a Tegra 3 Transformer tablet and that chip was yielded at 40nm, 2 generations behind Intels 22nm, and it has a TDP of 15 watts. Of course under load it would run higher than that, but so would an Intel chip.
- cmccabe 14y ago
  20W, 200W, what's the difference? Either way, you can't get that out of the battery on a mobile device. And consumers don't generally buy PCs based on power dissipation. Sad, but true. And if you think your typical beige-box PC can handle a power supply that is specc'ed for 150W-- go ahead and put one of those in there. I DARE you.
  - jrabone 14y ago
    The lower figure of 20W is pretty standard: go take a look at the battery in your laptop. Most Dells are 65Whr batteries - ie. 20W for 3 hours of battery life (to a first approximation, LiIon is a bit more complicated than that). The ubiquitous small form factor PCs like the Optiplex 780 (http://www.dell.com/downloads/global/corporate/environ/comply/optix_780_dccy.pdf http://www.dell.com/downloads/global/corporate/environ/compl...) use a 235W (max) power supply, which will be overspecced to trade off failure rates for manufacturing cost. Those machines actually draw less than 150W flat out. And they're everywhere. A certain large e-tailer with an emphasis on frugality used to use them as developer desktops(!). Who knows what's in a typical consumer beige box, but it isn't pulling 500W continuously, unless they're playing, say, Skyrim 24/7 with a big graphics card - in which case of course one would specify the correct (safe) component for the design. I'd argue that they're not typical by that point; most people won't spend £300 on a graphics card (I do).
    - cmccabe 14y ago
      So to recap: * You point a to 235W power supply as an example of the bare minimum PC power supply-- not too far from my 300W round number. * You point out that a power supply rated for X isn't drawing X continuously-- a true statement, but it's responding to an argument nobody made. You have to pick a power supply which is rated for your max load-- everyone knows that, or should. It still doesn't change the fact that both max load and average load for X86 are orders of magnitude greater than for most ARM devices.
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baq 14y ago
500 watts is a seriously overclocked with a sli/crossfire gfx setup or the super-high-end offerings like dual gpu on a single card. it's probably less than 1% of all desktop pcs. my ageing desktop with an e8400 and an radeon 4850 draws 270 watts at full load, including display - number straight from the ups.
Tsagadai 14y ago
What CISC legacy baggage? Most of the old and underused operations are emulated with microcode on modern x86 processors. Chip makers use profiling tools just like software makers, optimize the most common cases and your benchmarks improve. There are decades worth of engineering optimizations in Intel and AMD's chips. Intel has a massive engineering and R&D budget and competing with that is pretty damn hard. It has nothing to do with evolutionary heritage and more to do with you repeating ancient myths that haven't been remotely close to the truth of a decade.
- cmccabe 14y ago
  One example of legacy baggage is the fact that x86 doesn't reorder loads and stores as freely as ARM. It would be better for optimization, but it would break the creaky old software that is the lifeblood of the platform. Another example of "evoluationary heritage" is the fact that x86 chips require a northbridge and/or southbridge, whereas with ARM chips, everything is integrated on the chip. This was one reason why Atom-based designs often weren't that low power-- the CPU itself might be low-power, but the glue logic was thirsty. There is evidence that Intel is trying to change this, and put everything on one chip. I'm not trying to say that x86 will never succeed in mobile. I don't have a crystal ball. I'm just saying that the burden of proof is on Intel to prove that it can be cost and performance-competitive in that space. And I am not the only skeptic-- Apple and Microsoft use ARM for most of their mobile offerings.
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