AMD Phenom II X4 940 & 920: A True Return to Competition
by Anand Lal Shimpi on January 8, 2009 12:00 AM EST- Posted in
- CPUs
45nm and Low Power Consumption
Built on a 45nm process, Phenom II is finally using the same feature size as Intel’s processors. Intel’s 45nm caches are a bit smaller than AMD’s, but it’s no longer a 65nm vs. 45nm playing field - things are much more even. However, AMD and Intel’s approaches to 45nm differ considerably.
Circuits are placed on silicon wafers through the use of photolithography. Light is shone on a mask, and the light then makes it through the mask and etches the circuits on the silicon wafer. The wavelength of light used determines the minimum feature size of the circuits on the wafer. By itself, 193nm wavelength deep ultra-violet light is only useful for circuit feature sizes down to 50nm. To reach 45nm and beyond you need to do a little more.
AMD uses immersion lithography, which places a liquid between the source of the light and the wafer itself. The liquid increases the resolution at which the light can focus, allowing for smaller than 50nm feature sizes with currently available tools. Immersion lithography isn’t a performance enhancing feature; it’s simply one that makes it possible for AMD to manufacture at 45nm.
Intel claims that immersion lithography isn't necessary at 45nm and doesn't use it. Intel uses a technique known as double patterning but only on the gate layer of the chip. Intel’s approach requires higher mask costs but can result in a high yield 45nm chip without the use of immersion lithography. AMD’s approach should be more cost effective initially since you have to create fewer masks, but Intel’s scale of 45nm production should help offset that. For what it's worth, the double patterning has been in use since Intel's 65nm process.
Remember Intel’s high-k + metal gate transistor announcement? That’s still a feature advantage that Intel holds at 45nm. The new transistors make sure that current doesn’t flow when it’s not supposed to, reducing power consumption.
The two processes, despite both being 45nm, are different enough that they aren't the same despite having similar feature size - but comparing manufacturing processes is beyond the scope of this article.
A Power Efficient Phenom?
When Phenom first hit, not only was it underperforming, but it also drew far too much power. Combine that with a CnQ mode that robbed users of performance and you ended up with a CPU that was hardly power efficient. Just like the cache deficiency, Phenom II fixes this.
With Core i7, Intel developed power gate transistors that can completely shut off an individual core that’s not in use. Intel’s cache hierarchy is inclusive so any data stored within a core’s L1 and L2 caches is already duplicated in the L3 cache; if a core isn’t in use it can be shut down and there’s no need to wake it back up until it’s needed again.
Remember, Phenom II isn’t a complete redesign, so AMD couldn’t work on a similar technology. Despite that, idle power in Phenom II is greatly improved. When a single core is idle, the contents of its L1 and L2 can be flushed out to L3, allowing the processor to halt the clocks to that core - thus reducing power. The core will still consume leakage power, but it’ll be far less than if it were running at the lowest p-state. Intel introduced something similar back in the Conroe days, except data from L1 was pushed out to L2 before the core was powered down since there was no L3. Nehalem still has the ultimate in idle power thanks to Intel’s power gate transistors, but as you can see below Phenom II’s idle numbers are quite impressive.
| Processor | Idle Power | Load Power |
| AMD Phenom II X4 940 (3.0GHz) | 109.6W | 189.7W |
| AMD Phenom 9950 BE (2.6GHz) | 124.2W | 210W |
| AMD Phenom X3 8750 (2.4GHz) | 127.5W | 210W |
| AMD Athlon X2 6400 (3.2GHz) | 101W | 195W |
| Intel Core i7-965 (3.2GHz) | 99W | 199W |
| Intel Core i7-920 (2.66GHz) | 95W | 168W |
| Intel Core 2 Extreme QX9770 (3.2GHz) | 135W | 219W |
| Intel Core 2 Quad Q9400 (2.66GHz) | 126W | 174W |
| Intel Core 2 Quad Q8200 (2.33GHz) | 134W | 168W |
| Intel Core 2 Duo E8600 (3.33GHz) | 124W | 157W |
Note that while Penryn’s idle power isn’t nearly as low as Phenom II, this has more to do with Penryn’s lowest operating frequency. Phenom II’s minimum p-state is only 800MHz, compared to 2.0GHz on Penryn. Load power is also impressive, not quite Nehalem impressive but definitely competitive with Penryn at least.
In load power, Penryn still has the advantage. The Q9400 draws 174W compared to 190W for the Phenom II X4 940. The Core i7 is still the most power efficient of the two, as the i7-920 draws less power and is faster than the Phenom II X4 940.
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poohbear - Thursday, January 8, 2009 - link
this is fantastic news! and just when i was about to upgrade from my ancient s939 system to a C2D system, seems i might be sticking to AMD after all! thanks for review!PrezWeezy - Thursday, January 8, 2009 - link
For less than $20 more the i7 920 looks like it wins in every single test by a fair margin, doesn't seem like this is really all that competitive, considering the i7 is still in the "high price" phase. I can't believe it wont drop to the $275 mark rather soon which would put the XII 940 back to the same position the original Phenom was, too little too late.Roland00 - Thursday, January 8, 2009 - link
More expensive Motherboard+More expensive Ram makes i7 about 400 dollars more in coststrikeback03 - Friday, January 9, 2009 - link
How you figure? By the chart on page 4, it is less than $200. Even if you go for one of the $300 motherboards, you won't see a $400 difference.When I built my current system, E6600/P965/2GB DDR2 cost me over $600, and that was considered a decent mid-range system. As my primary use of computing power is Photoshop, I would definitely go for i7 even if cheaper motherboards do not become available.
Roland00 - Friday, January 9, 2009 - link
It isn't quite 400 but heremotherboard p45 vs x58 most x58 are 300 vs 100-120 for p45,
Ram, 6 gb of ddr3 is about 200, vs 50 or 60 for 6gb of ddr2.
For a nonstock cpu cooler you are talking 60 to 70 bucks with the i7 for it is a new socket and their is very few products for it. You can get a good cpu cooler for intel quad for 30 to 40 dollars.
Savings about 200+140+30=370
If you get things on sale you might be able to find 6gb ram for 150, cpu for 230, and you may be able to get the motherboard cheaper if you get one of the basic versions but you are still talking about 300 more.
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I am not saying i7 isn't worth the extra money, it is still new tech but it does show beneficial gains (on encoding, minimum frame rate on games, and overclocking) but right now the motherboards and ram is expensive.
BSMonitor - Friday, January 9, 2009 - link
You are rounding up on i7 side and rounding down on the core 2 side. It is not $50 for 6GB of DDR2. It is not only $300 for x58. I have seen them for $200. I have seen 6GB DDR3 kits for $140 too.It's like we are talking about bare entry into Core 2 and Phenom II, but enthusiest for i7. Why does one need 6GB to entry into i7? 3GB would be reasonable and ~$70-80.
Phenom II is cute yes, but nothing to jump on.
Roland00 - Friday, January 9, 2009 - link
I am rounding up on the I7 side for like most people I buy things with tax (for my state charges tax on internet transactions.) In addition many people buy their equipment in stores such as fry's, microcenter, comp usa, etc.370 times 8.25% tax rate (my area's sales tax) is...400 dollars and 52 cents
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And no I am not overpricing the ram or similar equipment. Go to Fry's, Microcenter, or some other store and you will see the prices I listed or much higher.
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Regardless you seem to be missing the point, the original poster I was responding to was saying i7 was only 25 dollars higher, and I said that was wrong for you have to figure in the platform costs.
PrezWeezy - Friday, January 9, 2009 - link
You were right, I had forgotten about the new socket and DD3. Even so, using the parts Anandtech used, the i7 is about $187 more expensive than the PII (pun totally intended). The C2D with a Q9400 though is only $44 cheaper than the i7. Almost all of that has to do with the motherboards used here, and I'm sure you could find a combo of motherboard/CPU that would bring the price closer but that's besides the point.calyth - Thursday, January 8, 2009 - link
"In theory, the AMD design made sense. If you were running a single threaded application, the core that your thread was active on would run at full speed, while the remaining three cores would run at a much lower speed. AMD included this functionality under the Cool 'n' Quiet umbrella. In practice however, Phenom's Cool 'n' Quiet was quite flawed. Vista has a nasty habit of bouncing threads around from one core to the next, which could result in the following phenomenon (no pun intended): when running a single-threaded application, the thread would run on a single core which would tell Vista that it needed to run at full speed. Vista would then move the thread to the next core, which was running at half-speed; now the thread is running on a core that's half the speed as the original core it started out on."Anand, read that sentence again.
The problem isn't AMD designing a chip with broken CnQ. The problem is that Microsoft, after so many years, still can't write a scheduler. The problem persists on XP too. The thread that handles the mouse would rev up, causing the chip to switch p-state. Switching p-states takes time, and because of exclusive caching on AMD chips, when the scheduler puts the same thread on different cores, it causes the L1 & L2 to be ineffective.
I have trouble in WinXP with CnQ on if I move my mouse, but not surprisingly, the same Phenom chip works like a chap in Linux. Because the scheduler isn't an idiot, and 1GHz is more than enough to handle mouse input.
AMD erred in fixing a software problem in hardware. Independent p-states saved some power if only a single thread needed the speed.
Zak - Thursday, January 8, 2009 - link
Well, I hope AMD won't lose the momentum, because right now there isn't that much to celebrate: they've barely caught up with Intel's 2 years old CPU line:(Z.