Sandy Bridge laptop - dual core vs quad core

[skaertus]

I intend to buy a new laptop this year, following the lauch of the much-anticipated Sandy Bridge. I bought my last laptop, which sports a Core 2 Duo T8300 2.4 GHz processor, in 2008, and, although it still handles most tasks quite well, I could definitely benefit from a significant speed boost. However, this decision became more imminent since my laptop had its screen damaged last week. I can certainly have my screen repaired, but that there is no point in fixing it if I am going to replace the laptop anyway.

I've noticed that there are some new laptops with a quad-core Sandy Bridge processor. I've read some tests and even the i7-2630QM (which represents the low-end of these processors) seems to be faster than any Clarksfield (even the almighty i7-940XM).

In addition, this processor seems to be more power-efficient than the Arrendale. I've read reports that a Sager NP5160 sporting an i7-2630QM has a battery life of 4.5-5 hours or even 6 hours (with NVIDIA GT540M disabled). That's a lot of time, considering that the battery of previous Sager notebooks would be drained after only 2 hours of use or even less.

I understand that this increase in battery life comes, to a large extent, from the gymnics Intel has done with its integrated graphics. However, as far as I am concerned, quad-core processors still consume more power than dual-core processors. A Core i7-2630QM has a TDP of 45W; the dual-core Sandy Bridge, on the other hand, will have a TDP of 35W. I have no doubt that the dual-core Sandy Bridge would be more power-efficient than the quad-core. But I wonder how much more efficient it will be.

I am not aware of any tests or reviews of dual-core mobile Sandy Bridges nor of any report of Intel on this respect. No real facts, just thoughts posted in forums. I've read thoughts that a dual-core Sandy Bridge would allow notebooks with an 8-hour battery life. But I've also read that most of this power efficiency comes from the integrated graphics and that a dual-core Sandy Bridge would not allow a significant increase in battery life over the quad-core Sandy Bridge (it would be about half an hour). While I believe the truth is in the middle, I would like to further investigate this matter, so I can decide whether to buy a laptop with a quad-core Sandy Bridge now or wait until the dual-core is available.

Any thoughts on this issue? I would much appreciate if someone had more information (real facts) on this. Thank you in advance.

 

[Stuka87]

I have been going over the same thing in my mind. To get a quad or a dual. For me I think it may come down to how much of a cost difference there is.

I could make use of a quad core in the work that I do, but not if the battery life is destroyed in the process. I am anxiously awaiting Anands reviews of SB laptops.

 

[skaertus]

About cost difference, I may be wrong, but I suspect that the cost of a dual-core Core i7 and a low-end quad-core Core i7 won't be very different. If you take Nehalem as an example, the Core i7-640M costs US$ 346 and the Core i7-740QM costs US$ 378. It's a difference of less than 10% and I can deal with that (of course Core i3 and i5 processors will be cheaper, but they will also be slower). It also seems to me that these two i7 processors are quite similar in raw power, but in different ways: the dual-core is faster for single-threaded applications, while the quad-core would be better for multi-threaded applications. All in all, the more multi-threaded the applications are becoming, the more it will make sense to have several cores. I might be wrong, though.

Quad-core Sandy Bridges seem to be quite power-efficient. I would much appreciate a laptop with a Core i7-2630QM and with a battery that could last for 5 hours. But then, how power-efficient will the Core i7-2620M be? It might not be as fast as the Core i7-2630QM, but will it allow a battery life of 8 hours? If it does, it might be worth it.

 

[somethingsketchy]

I'd say it really depends on your tasks that you want to do on your laptop. If you are only going to be surfing the web and no real video streaming, you can probably get away with a dual core and get as much battery life you can.

Otherwise if you intend to photo/video rendering, or any CPU intensive task, go with a quad core.

When it comes down to it, it's your work load that should determine what kind of CPU to get, not how much battery life you can get.

 

[skaertus]

I'd say it really depends on your tasks that you want to do on your laptop. If you are only going to be surfing the web and no real video streaming, you can probably get away with a dual core and get as much battery life you can.

Otherwise if you intend to photo/video rendering, or any CPU intensive task, go with a quad core.

When it comes down to it, it's your work load that should determine what kind of CPU to get, not how much battery life you can get.

Well, in fact, I can make good use of a quad-core laptop. I'm quite a heavy user and I feel my Core 2 Duo T8300 laptop can't handle things as well as I want it to do. I would love to put my desktop Core i7-870 (or the 2600K now that it's available, or even the i7-980X if I just had the money) inside a laptop and carry it around.

I go to meetings with my laptop, and I frequently have to use virtual machines and other intensive tasks - and using a virtual machine with four cores is so much better! However, it is very common for me to stay unplugged during those meetings, so a long battery life is very useful. On the other hand, I simply can't use a netbook or a low-voltage laptop (and benefit from its many-hour battery life) because it lacks performance.

That is why I am concerned about battery life. I want the best performance/battery life ratio that I can find. And I found out that those quad-core Sandy Bridges (such as the i7-2630QM) have a better battery life than the much slower dual-core Nehalems (such as the i5-580M or the i7-640M). Now I would like to know whether the i7-2620M will have much better battery life than the i7-2630QM.

 

[Zap]

Quad-core or Dual-core ? Which one do I pick ?

 

[skaertus]

Quad-core or Dual-core ? Which one do I pick ?

Thanks, that's a great thread, but that's not precisely the point here.

In fact, I've had at least three dual-core laptops, a dual-core desktop and now I own a quad-core desktop. I know the differences between a dual-core and a quad-core in terms of performance in single-threaded and multi-threaded applications. For my use, I would greatly benefit from a quad-core processor, but I would also benefit from a great battery life.

My doubt here is much more specific. I already know that a Core 2 Quad drags more power than a Core 2 Duo; and that a quad-core Core i7 drags more power than a dual-core Core i3/i5/i7. Accordingly, in what concerns Core and Nehalem processors, a laptop with a dual-core chip has a substantially larger battery life than a laptop with a quad-core chip.

But it seems like Sandy Bridge, the new generation of Intel processors, is a game-changer. At least it is what I've been reading. A quad-core Sandy Bridge seems to be very power-efficient, as it drags less power than a dual-core Arrendale. A laptop with a quad-core Sandy Bridge is capable of 5-6 hours of battery life, and that's unprecedented for a quad-core laptop. I would like to know how much battery life will a dual-core Sandy Bridge allow. If it keeps pace with the previous generations of Intel chips in what concerns dual/quad core differences, it may allow for 8-10 hours of battery life. But I guess that the difference will be less significant, as the quad-core Sandy Bridges have the power-efficiency enhancements of the dual-cores and also use the integrated graphics. In addition, quad-core Nehalems (Clarksfield) were made using the 45nm process, while dual-core Nehalems (Arrendales) were made using the 32nm process, and this would make these processors more power-efficient, hence the better battery life. In Sandy Bridge, this would not happen.

As you can see, my doubt is about battery life differences between Sandy Bridge dual-core and quad-core processors, and not between dual-core and quad-core processors in general. Any thoughts on that?

 

[IntelUser2000]

The dual core mobile Core i7 2nd Gen chips aren't out yet that's why the infos are scarce. I assume there will be 25% battery life difference between SV 35W dual and 45W quad in demanding apps and 10-15% in idle. That's from the power specs.

 

[skaertus]

The dual core mobile Core i7 2nd Gen chips aren't out yet that's why the infos are scarce. I assume there will be 25% battery life difference between SV 35W dual and 45W quad in demanding apps and 10-15% in idle. That's from the power specs.

That makes sense. If we look at a comparison between the i7-2630QM (TDP 45W) and the i7-2920XM (55W), the latter would consume more energy in tasks that use the extra energy: http://www.notebookcheck.net/Review-Intel-Sandy-Bridge-Quad-Core-processors.43714.0.html. I guess that the difference between quad-cores and dual-cores would be quite similar to this pattern.

 

[beginner99]

Well, in fact, I can make good use of a quad-core laptop. I'm quite a heavy user and I feel my Core 2 Duo T8300 laptop can't handle things as well as I want it to do. I would love to put my desktop Core i7-870 (or the 2600K now that it's available, or even the i7-980X if I just had the money) inside a laptop and carry it around.

I go to meetings with my laptop, and I frequently have to use virtual machines and other intensive tasks - and using a virtual machine with four cores is so much better! However, it is very common for me to stay unplugged during those meetings, so a long battery life is very useful. On the other hand, I simply can't use a netbook or a low-voltage laptop (and benefit from its many-hour battery life) because it lacks performance.

That is why I am concerned about battery life. I want the best performance/battery life ratio that I can find. And I found out that those quad-core Sandy Bridges (such as the i7-2630QM) have a better battery life than the much slower dual-core Nehalems (such as the i5-580M or the i7-640M). Now I would like to know whether the i7-2620M will have much better battery life than the i7-2630QM.

Are you sure it's the cpu that is slow? with 4 VM's I would also consider the HDD becoming a real bottleneck. Even running just 1 VM on the same hdd as OS isn't perfect but 4? I assume your laptop has at max 2 drives if at all.

I mean thats the point of VM's in servers. You have too much cpu power, so pack on like double (or more) the amount of vm's than the server has cores. The limiting thing is RAM and disk but mostly not cpu power.

Of course if you do encoding on all 4 vm's or some heavy benchmarking it's a different story but just running 4 VMs won't need a lot of cpu power.

BTW I will probably get a SB laptop too and ask myself the same question. But I'm leaning towards a dual core depending on price and battery life differences and availability. Need one rather soon.

 

[flensr]

2 concepts you need to understand though.

1. TDP is not idle performance. TDP is what it uses at max speed. Idle power use may not be so far apart, depending on how intel worked it out.
2. "race to idle" is a term that means a faster cpu with higher power consumption might actually use LESS power than a slower cpu, because the faster cpu drops back to idle sooner. A quad core cpu might actually use less power than a dual core cpu when doing tasks that intermittantly load the cpu near 100%, because the quad would finish and drop to idle sooner.

In my experience with non-gaming laptop usage, faster cpus of the same generation don't burn all that much more power, especially now that intel is putting so much effort into optimizing power consumption. Yes a quad core will probably use more power at idle than a dual core cpu, but it will also probably spend more time at idle too, depending on what you're using it for. If you keep it loaded at 100% all the time or if the cpu sits at idle most of the time, then the dual core will be more efficient. But the difference will be a lot smaller if your cpu sees more varying loads most of the time.

Again in my experience, the drop in battery life going with a faster cpu in the same processor family is more than compensated for with the faster speed. As for price, all the media reports I've seen so far seem to show sandy bridge cpus to not be super expensive. If you're that close to your margin on cost and that last 20 minutes of battery life really is a big deal for you, then maybe you should get the slower cpu and a second battery instead of the faster cpu. But for lots of people, the faster cpu might be better in the long run because you won't feel pressured into upgrading quite as soon.