For all of modern Intel history, it has specified a TDP rating for all of its silicon. The TDP rating is given at a specific max core temperature (Tj_MAX) so that OEM chassis designers know how big to make their cases and what sort of cooling is necessary. Generally speaking, anything above 50W ends up in some form of a desktop (or all-in-one) while TDPs below 50W can go into notebooks. Below ~5W you can go into a tablet (think iPad/Nexus 10), and below 2W you can go into a smartphone. These are rough guidelines, and there are obviously exceptions.
With Haswell, Intel promised to deliver SKUs as low as 10W. That's not quite low enough to end up in an iPad, but it's clear where Intel is headed. In a brief statement at the end of last year, Intel announced that it would bring a small amount of 10W Ivy Bridge CPUs to market in advance of the Haswell launch. At IDF we got a teaser that Intel could hit 8W with Haswell, and given that both Haswell and Ivy Bridge are built at 22nm with relatively similar architectures it's not too far of a stretch to assume that Ivy Bridge could also hit a similar power target. Then came the CES announcement: Intel will deliver 7W Ivy Bridge SKUs starting this week. Then came the fine print: the 7W SKUs are rated at a 10W or 13W TDP, but 7W using Intel's Scenario Design Power (SDP) spec. Uh oh.
Let's first look at the new lineup. The table below includes both the new Y-series SKUs as well as the best 17W U-series SKUs:
Low TDP Intel Core Processor Comparison
  Pentium 2129Y Core i3-3229Y Core i5-3339Y Core i5-3439Y Core i5-3317U Core i7-3689Y Core i7-3517UE
Nominal TDP 10W 13W 17W 13W 17W
cTDP Down - 10W 13W 10W 13W
SDP 7W - 7W -
Cores/Threads 2/2 2/4
Base CPU Clock 1.1GHz 1.4GHz 1.5GHz 1.5GHz 1.7GHz 1.5GHz 1.7GHz
1C Turbo - - 2.0GHz 2.3GHz 2.6GHz 2.6GHz 2.8GHz
2C Turbo - - 1.8GHz 2.1GHz 2.4GHz 2.4GHz 2.6GHz
L3 Cache Size 2MB 3MB 4MB
GPU HD HD 4000
Base GPU Clock 350MHz
Max GPU Clock 850MHz 1.05GHz 850MHz 1.1GHz
Quick Sync No Yes
VT-d No Yes
VT-x Yes
Socket FCBGA-1023
Price $150 $250 $250 $250 $225 $362 $330
Compared to a similarly configured U-series part, moving to a Y-series/7W part usually costs you 200MHz in base clock, ~250MHz in max GPU clock, and 200 - 300MHz in max turbo frequency. Cache sizes, features and Hyper Threading are non-negotiable when going between U and Y. The lower clocks are likely the result of lower operating voltages and a side effect of the very low leakage binning. The cost of all of this? Around an extra $30 over a similar U-SKU. That doesn't sound like much but when you keep in mind that most competing ARM based SoCs sell for $30 themselves, it is a costly adder from an OEM's perspective.
Now the debate.
Intel should have undoubtedly been very specific about 7W being an SDP distinction, especially when the launch slide compared it to TDPs of other Intel parts. Of course Intel failed to do this, which brought on a lot of criticism. To understand how much of the criticism was warranted we need to first understand how Intel comes up with a processor's TDP and SDP ratings.
Intel determines a processor's TDP by running a few dozen workloads on the product and measuring thermal dissipation/power consumption. These workloads include individual applications, multitasking workloads (CPU + GPU for example) and synthetic measures that are more closely related to power viruses (e.g. specifically try to switch as many transistors in parallel as possible). The processor's thermal behavior in all of these workloads ends up determining its TDP at a given clock speed.
Scenario Design Power (SDP), on the other hand, is specific to Intel's Y-series SKUs. Here Intel takes a portion of a benchmark that stresses both the CPU and GPU (Intel wouldn't specify which one, my guess would be something 3DMark Vantage-like) and measures average power over a thermally significant period of time (like TDP, you're allowed to violate SDP so long as the average is within spec). Intel then compares its SDP rating to other, typical touch based workloads (think web browsing, email, gaming, video playback, multitasking, etc...) and makes sure that average power in those workloads is still below SDP. That's how a processor's SDP rating is born.
If you run a power virus or any of the more stressful TDP workloads on a Y-series part, it will dissipate 10W/13W. However, a well designed tablet will thermally manage the CPU down to a 7W average otherwise you'd likely end up with a device that's too hot to hold.
Intel's SDP ratings will only apply to Y-series parts, the rest of the product stack remains SDP-less. Although it debuted with Ivy Bridge, we will see the same SDP ratings applied to Haswell Y-series SKUs as well. Although Y-series parts will be used in tablets, there are going to be some ultra-thin Ultrabooks that use them as well. In a full blown notebook there's a much greater chance of a 7W SDP Ivy Bridge hitting 10W/13W, but once again the burden falls upon the OEM to properly manage thermals to deliver a good experience.
The best comparison I can make is to the data we saw in our last power comparison article. Samsung's Exynos 5 Dual (5250) generally saw power consumption below 4W, but during an unusually heavy workload we saw it jump up to nearly 8W. While Samsung (and the rest of the ARM partners) don't publicly specify a TDP, going by Intel's definition 4W would be the SoC's SDP while 8W would be its TDP if our benchmarks were the only ones used to determine those values.
Ultimately that's what matters most: how far Intel is away from being able to fit Core into an iPad or Nexus 10 style device. Assuming Intel will be able to get there with Ivy Bridge is a bit premature, and I'd probably say the same thing about Haswell. The move to 14nm should be good for up to a 30% reduction in power consumption, which could be what it takes. That's a fairly long time from now (Broadwell is looking like 2H-2014), and time during which ARM will continue to strengthen its position.
Acer's W700 refresh, with 7W SDP Ivy Bridge in tow
As for whether or not 7W SDP parts will actually be any cooler running than conventional 10W/13W SKUs, they should be. They will run at lower voltages and are binned to be the lowest leakage parts at their target clock speeds. Acer has already announced a successor to its W700 tablet based on 7W SDP Ivy Bridge with a 20% thinner and 20% lighter chassis. The cooler running CPU likely has a lot to do with that. 
Then there's the question of whether or not a 7W SDP (or a future 5W SDP Haswell/Broadwell) Core processor would still outperform ARM's Cortex A15. If Intel can keep clocks up, I don't see why not. Intel promised 5x the performance of Tegra 3 with a 7W SDP Ivy Bridge CPU. Cortex A15 should be good for around 50% better performance than Cortex A9 at similar frequencies, so there's still a decent gap to make up.
At the end of the day, 7W SDP Ivy Bridge (and future parts) are good for the industry. Intel should have simply done a better (more transparent) job of introducing them.
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  • Mugur - Monday, January 14, 2013 - link

    It's wrong whether there is a possibility, however remote, to manage to squeeze the chip to more than 7W and blow any thermal solution calculated for this...

    But I wonder if this is actually possible, because of the lowered frequency and voltage.
  • R0H1T - Monday, January 14, 2013 - link

    It seems to me you're trying to cover that epic fail over here ~

    I dunno but when it comes to the chipzilla everyone, especially on AT, feels that they(Intel) are so far ahead vis-à-vis the rest of the pack that they might as well stomp over the competition if the antitrust laws would allow'em to do so in the first place aye ? This isn't the case clearly proven by the 32nm SOI Vishera beating i5 at 22nm trigate not to mention the exynos 5x beating anything the Atom has to offer, IIRC the former is half a node back as well, which shows the bias or fanboyism synonymous with the iSheep !
  • scottjames_12 - Monday, January 14, 2013 - link

    On which planet does Vishera beat IVB, especially when it comes to power efficiency? /trollfeeding
  • R0H1T - Monday, January 14, 2013 - link

    Who said anything about power efficiency ? Check performance numbers & benchmarks on any of the sites out there including AT, just FYI single threaded performance doesn't count (cause frankly its a sick joke nowadays) as multicore CPU's are supposed to run stuff on more than one core !

    /not impressed, shrugs off !
  • scottjames_12 - Monday, January 14, 2013 - link

    Oh my apologies, I though seeing as the article is mainly concerning TDP's and power efficiency, that your comment might be on topic.. my bad.

    It is good to see AMD being competitive with heavily threaded workloads. It's a shame that heavily threaded workloads are still so specialised, explaining why Vishera falls behind in the regular benchmarks which are more relevant to just about everyone. Single threaded performance doesn't count? LOL. Ok...
  • R0H1T - Monday, January 14, 2013 - link

    I think you're confused here, or maybe that's just me, anyways here is what I said ~

    1) AT refuted the fact, rightly so mind you, that Intel won't be getting IVB or Haswell in the 7W power envelope cause that's the best case scenario taking mostly light(er) workloads in mind which really isn't how their usual TDP is measured !

    2) The fact is Intel isn't so much ahead of the competition that they can do whatever they'd want to, as most of the AT readers would like to imagine, so incase of ARM they're lagging on the performance front vis-à-vis top of the line Exynos or even Apple's custom made Swift SoC all other things being equal. For AMD they have a full node advantage on the x86 front so really its a no brainer as to why they're more efficient & certainly this Bulldozer architecture has more potential for refinement than the nearly decade old core microarchitecture that has shown signs of aging as proven by the minimal gains of IVB over SNB !

    Lastly if you're so concerned about single threaded performance then why not get a "ye olde" celeron & overclock it to ~8Ghz or so for getting more out of those inefficiently coded programs ? I'll reiterate this ~ just because the software front is lagging doesn't mean that AMD is to be held accountable for their deficiencies !
  • scottjames_12 - Monday, January 14, 2013 - link

    1) Um, does it really matter? If the part has a lower heat output that enables usage in thinner and lighter devices (than the U series parts) does it really matter how the rating is calculated? These parts will be able to be used in devices that are designed to dissipate 7W. Sure, you'll be able to make it exceed 7W with a power virus, but I'm sure they will have something along the lines of configurable TDP that would keep the heat under control.

    2) Who is saying that they are? Although certainly if you look at market share and shipments, it is easy to draw the conclusion that Intel are the ones to beat. I personally don't care or play favourites. I buy whatever is best when I've got money to spend. And regarding IVB vs SNB, you know that IVB was a tick.. right?

    Your last paragraph is pretty childish, really (which is funny, considering your post title). Most people aren't going to buy a processor that is slower 95% of the time, based on the hope that software more suited to it's architecture is 'coming soon'.
  • R0H1T - Monday, January 14, 2013 - link

    IVB was a tick indeed(no pun intended) however it failed to deliver the desired performance gains expected by the majority of users(enthusiasts mainly) which sorta points that the headroom is limited in this case for Intel so AMD will indeed close that inevitable gap(fingers crossed) as & when they move onto 22nm or smaller process nodes.

    Its hard to say whether you're being serious or sarcastic on that single threaded point ! Anyone who's looking for a better single threaded performer(CPU) against one that can perform better at multithreading is clearly going backwards & I think you that too right ?
  • scottjames_12 - Monday, January 14, 2013 - link

    Unfortunately for AMD, they seem to always be a step behind Intel when it comes to process nodes. Sucks for them but that is life. Perhaps Piledriver on a 22nm process would be faster than IVB in all areas, but Intel will have Haswell by then, which should see a bigger performance increase than IVB over SNB. Time will tell.

    I was definitely serious about the threaded point. Just forget 'single vs multithreading' for a moment. The facts are, IVB is faster than Vishera in most usage cases. And it's not like IVB is bad at heavily threaded workloads - when Vishera wins, it only just wins. On the flip side, when Vishera loses, it tends to lose badly. Only a fool would think that single threaded performance doesn't matter, especially when you consider certain types of workloads can't be multi-threaded.
  • R0H1T - Monday, January 14, 2013 - link

    I'd say quite alot of consumer level apps are multicore optimized these days also there's only so much an app can do on a single core. If an app is not scaling well on 2 or more cores then you can pretty much bet that there are better alternatives out there, unless its one of a kind, so yes whilst single threaded performance is an important metric in most benchmarks I certainly wouldn't give it no more than a 10% weightage at any given time !

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