Why Buy Core i7 Over Core i5?

Looking at several of these new notebooks coming out, I am finding it hard to imagine why anyone would buy i7 over i5. Here is a list of the comparisons of the two, stop me if I am wrong:

Core i5 Pros:
Lower power consumption
Lower heat production
Much higher clock speeds

Core i7 Pros:
2 more physical/4 more logical cores
Larger L3 Cache

I am aware hyperthreading is not as efficient as having additional physical cores, but it still works pretty darn well. To step up from the best i5 to the entry level i7 increases cost, you loose almost one full gigahertz(2.53->1.6), and loose battery life. Unless someone is doing alot of audio/video encoding, I can't for the life of me think of why anyone would choose an i7, even for bragging rights.

 

My i7 720 runs very cool... it I run multiple apps at once, doesn't my i7 perfrom better?

Also, I am not sure if this is true for all vendors, but Lenovo offers USB 3.0 only on the i7.

I assume that this wont be true forever.

I think for PC the i7 is clearly better - you are only asking for laptops?

R

 

Nobody said the Core i7 was meant to be practical.

It is meant to deliver performance performance performance, with little regard for other factors. This is simply because that's all the consumer will care about.

 

I also wonder which one is better (1.6 corei7 or 2.53 corei5), specificly for gaming.

 

That should be a given that I am asking for laptops given the nature of the forum, but yes for laptops only. For desktops absolutely I would choose i7, but there you don't have to choose between higher clocks/heat/battery life.

And realistically you will not see a performance jump if you are running multiple apps from an i5 to an i7 as the multitasking ability is up to the thread scheduling of the OS itself. You might see a small increase, but then quite a few applications are also going to prefer the i5s much higher clock speed.

But that is my point, do you not see a reduction in performance in the vast majority of scenarios due to the much lower clock speed?

 

No. The Core i7 emphasizes performance through multi-threading, not through clock speed.

 

With two cores, running, the i7 will have the same clock speed. Or close to it depending which i7 you get.

 

The speed difference may not be quite as large as you think; (assuming adequate cooling) with turbo-boost the i7-720QM on 2 cores (to match the i5) gets up to 2.4 GHz.

Given the ability to essentially fully shut down cores, you actually won't be losing that much battery life comparatively, given similar loads. At this point, it really depends on what kind of loads you're putting on them. At idle, both should be operating on one core only, at minimum speed, so unless there's a power improvement in the power requirements of a single i5 core vs a single i7 core (unknown) idle power consumption is likely to be similar. With loads, it depends on how well threaded and what kind of load is being put on the processor. If it's multiple threads, the i7 may be able to finish on par or faster due to having more processors to run the threads simultaneously, even if each individual thread runs slower, and thus return to an idle state faster than the i5.

In general, however, yes, it is true; most people have no real need for the full processing power of an i7, and an i5 will do just fine for them. Actually, a C2D will do fine for most people, but that's no longer popular because it's "obsolete".

 

A Pentium M is fine for me.

I probably wouldn't accept anything less than a PM though, as the next step down is a dreaded Pentium 4. Oh, the horrific memories of using that processor.

 

There are more i7 Arrandales then there are i5...or i7 quads for that matter...but no one hardly ever talks about them.

 

I would buy i7 for more performance , especially quad... but seriously how does multi threading help so much compared to clockspeed? For a generation which is used to hearing that the best CPU has the highest clockspeed , this is a little alien concept for me.

 

Lets say you have process A that consists of threads B, C, and D running on a single core CPU can only work on one task at a time. The obvious performance problem here is compounded by the fact that thread B may be waiting on an output from thread C, which in turn is dependent on an output from thread D, and so and so forth; you have a number of interdependent threads or even processes. The result is that a single core CPU is like a single assembly line, capable only of working on one task at a time, and is therefore a bottleneck in terms of working on multiple tasks. This is a practical problem for the vast majority of people who work on multiple tasks at a time on their computer.

One would naturally think that the solution is simple to speed up the single assembly line so that it can work on that one task much faster. But with silicon microprocessor technology, the problem is that increasing the clock speed is only feasible to a limited extent. Past a certain point, you run into theoretical and practical barriers such as heat management, power consumption, rogue electrons, etc. So increasing the clock speed is not possible, and making the process more multi-threaded does nothing for us on a single-core processor.

Read more technical explanations on these limitations from the University of Waterloo: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=00915372

The solution is to add more cores or logical cores (ie, HT), each running at a reasonable clock frequency. Now rather than one fast assembly line that is running at the maximum physical speed barrier, we have multiple assembly lines running at a reasonable speed and splitting the process into multiple threads. The result is that, by working smarter rather than harder, you can complete as a task in less time by splitting the task into smaller pieces and working on them individually. Furthermore, you have less wait time between interdependent process and threads while also staying within an acceptable frequency envelope.

An equivalent analogy is a student (since I'm a university student) working on one project. I can only work so fast while only working on one component of the project at a time. However, this is very stressful for me and I'm not going to meet the deadline for the project. The solution is to recruit some friends around me and split the project into individual tasks for each helper. That way, we can all work at a reasonable pace without killing ourselves, and at the same time the project is completed well within the deadline.

I hope this explanation makes sense, but keep in mind that I don't do the kinds of things I mentioned in my analogy.

 

@Bog
You have to be careful with that student analogy for two reasons.
1)Not every project can be divided up between people, some can only be accomplished by a single student.
2)Some projects might have a bad scheduler/divider between students(the operating system). Meaning some project parts might still be relegated to a single student with one student not doing anything, some might be evenly distributed. This would mean you won't necessarily get to take advantage of the turbo boost ability of the processors.

 

If all you are looking for is single threaded performance either will do. Now if power consumption is your main enemy then go with an i5, or if your a multitasker then go for the i7.

Those days just ended for me as my linux server ran on an OC'd 3.2HT p4 at 3.6GHz. I bought an averatec laptop in 2005 that with an original turion 1.6GHz that blew the OC'd p4 out of the water. When I thre the mt40 in it was game over for the desktop and it went to the wife and evenetually made into the server it was at work.

 

Yes, those are details to take into consideration. I use analogies because they simplify things, though.

 

Unfortunately, those details you simplified out are the vast majority of cases. Very, very few jobs have good symmetric thread loads. The only one most people are likely to run into are 3D image rendering and movie transcoding. Everything else, games and the like, will have very uneven thread loads. Given that the i5 can run up to 4 threads there are vanishingly few applications where an i7 will serve the majority of users better than an i5.

 

ran cinebench R10 on 720 the other day, it did it in 1min 55sec, which is pretty nice considering desktop Q9550 did it in 1:35 and Phenom 955 in 1:31.
I'd say, mobile i7 is quite handy for people that need high computational resources on the go and i5 would be absolutely enough for everything else IMO

 

The higher clocks of the Arrandale i5/i7 compensate for the fact that they have only 1/2 as many cores as Clarksfield i7.

Suppose you have a well-threaded app which scales linearly and for which overhead from threading is negligible.

Let us run the app on the 720QM. All four cores are in use, the 720QM can turboboost by at most one bin, so at most it can run at 1.73 GHz.

Compare that, say, to the fastest Arrandale, the i7-620M. When running that same well-threaded app on the 620M, both cores are in use, and it can turboboost by at most two bins, so at most it can run at 2.93 GHz.

Note that, in this scenario, the dual core clocks more than 70% faster than the quad core. If the dual core could clock 100% faster than the quad core, both processors would provide the same performance (at least for our hypothetical app).

The story I just told sort of explains what happens when you compare Cinebench R10 (multithreaded) results. The 720QM is a bit faster. ...but not that much faster because the 620M has this huge clock speed advantage.

OTOH, when you run an app that must run serially, the 620M kills the 720QM due to its clock advantage (3.33 GHz vs 2.8 GHz with max. turboboost).

When you can make use of (only/exactly) two cores, the 620M's advantage is even bigger.

So the above explains why the performance of the fastest Arrandales approaches (and sometimes exceeds) that of the cheapest Clarksfield. Now take into account the other advantages of Arrandale discussed by other people ^^^ All of that together makes the top-of-the-line Arrandale's better mobile processors imo

 

Do you think there will be a Arrandale xtrem someday?
That could be nice!
I (will) have the i7, and I'm happy! In the future more and more games will be running on 4 cores! It can just be a good investment for now!
And since then, as long as I dont see my 2k laptop lagging, I'll be happy!

 

you guys have managed to put to rest a lot of my concerns about the i5. I expected the natural progression would have been towards quad cores...and that dual cores must be a dying breed. I had no idea most apps were still not able to take advantage of quad.

I had written off the upcoming MacBook Pro because it's not going to have an i7 in it. I'll be giving it another real look now.

 

Here's my take:

1) If you NEED quad core, you'll know it and you won't have to wander around forums looking for advice.

2) If you aren't sure if you need quad core, and you normally buy a new laptop every 2 years, get a dual core.

3) If you aren't sure if you need quad core, and you normally keep your laptop as long as possible, get a quad core.

 

intel's naming scheme is really annoying. core i7 could mean both quad core i7 ( 720 - 920) and dual cores ( 620m, lv and ulv parts).

i am most intrigued by i7-620m. turbo at 3.33ghz and 35w tdp with imc and in built switchable gfx. quad cores have higher tdp plus have no built in gfx.

 

i thinkthe only way to answer this is through benchmarks of an i5 and i7 in the same machine, if thats even possible.
right now however, there seem to be a few programs that are optimized for quad cpu's.
this could change pretty soon though.

 

Correcting one error in the otherwise excellent post, the i7-620M can Turbo Boost up to 3 bins(400MHz) to 3.06GHz in dual core mode.

 

+1 to point #3. That's the way I would do it too.

 

Not to mention the much more aggressive Turbo Boost, that goes from 1.6 to 2.8 in the 720QM.

i7, as said is much more into the performance area. For renders and multi-threaded apps, the i7 beats the i5. On regular usage, the i5 is the one to go. If you ask me, unless you are really going to fully utilize the i7, go with the i5.

 

Here's the thing, I use my computer for mostly regular stuff, but I use it a lot. Similarly, I like to have a lot of things running at the same time. And I may start gaming. Add on top of that the fact that I like to keep laptops for at least 3-4 years (the one I'm on now will be 5 this summer). You would recommend the quad i7?

 

No. I dont see you fully using the 8 threads. My vote goes to Arrandale, i7 Arrandale I would choose, but i5 suits the needs just fine.

I notice you have ordered the 720QM, dont get me wrong, it is by no means a bad CPU, and with some tweaking, temps can really drop to mroe than acceptable numbers, I have even hit the 32C in a 10-15C temp room, when almost idling. Considering this is a quad core, and I was using passive cooling, it is not bad at all. But as I said, I rarely see it hit the 30% usage. In fact, only when benchmarking it, and yesterday while rendering I got it to fully use the 8 threads and work at 100% of capacity. But on regular tasks, surfing the web, writing something, foruming, I dont even hit the 15%...

Now, why would I choose Arrandale now? The smaller die should mean lower temps, not to mention that (if enabled) the IGP+GPU combo would really satisfy me, and give more battery life than the lack of it.

So, I see it this way, pure, raw, high performance is Clarksfield. A more sensitive, less power hungry, and somewhat more advanced (in terms of age) the Arrandale seems a better fit. So, what are your needs?

 

I would love Arrandale, but it wasn't available in the computer I ordered, and I love everything else about that computer. Is quad going to be a problem for me?

 

Maybe a quad would be more future-proof in terms of performance. But wouldn't the higher TDP make it more prone to failure? If you want your laptop to last for 4-5 years, isn't that important too? I'm really not sure, I'm just asking.

 

If properly designed it's not more prone to failure. I'm just not seeing any major changes in the next 5 years that will give the majority of people any benefits over the 4-thread capabilities of the dual-core Arrandales.

 

i'm all into over kill. i'd go for the i7 just because it's faster. whether or not i'll need or use the speed is another question.

i'm sure 90% of ferrari owners don't test the limits of their cars. lol

 

Not necessarily. CPUs can take temps of 100C IIRC without suffering any damage, though it is better to have it under lower temps.

On the other hand, the GPU is more prone to failure due to temp cycles, which damage GPUs eventually (main cause of the NVIDIA 8400 and 8600 fiasco), but dont worry, ATI has not had this problems, not that we are aware of at least.

Well, if you check, Intel seems to stand by 2x2 (core and HT) for some time, this means that the urgency for a quad core is nowhere near immediate. Not to mention that the amount of applications actually using more than 2 threads are still rare, even less using 8 threads. So with Arrandale 2x2 you will be safe IMHO. 4 threads is enough. It behaves as a quad core when needed and if possible. So you get quad core performance, without the quad-core penalties (of "yore" lol).

 

Thanks for the excellent explanation. It was simple and had everything u needed to know. Looks like next comp has a quad for sure.

 

As Bog says it, having more cores does help, but only to a certain point.

I dont want to diminish Bog's explanation, because theoretically speaking is very well done, and represents reality to some extend. Now, when applying this into real life components in a laptop there is a the software variable. Very much like the assembly line (the CPU), we have to take into consideration the product we are doing (the software). Not because I have 20 lanes to work means all the products I do will end up faster, since some things being produced require less lanes to work with.

So, in an applied situation, the CPU has 8 threads running (case of Clarksfield). This would be like the assembly lines, you have 8 assembly lines to use. Ok, now you launch an application on your computer. This is what is going to be produced in your assembly lines. This software launched would run a lot faster on the 8 threads in theory, but in reality, it cannot run on more than 2 threads. It would be like the constraints on a mechanical piece, you cant do all at a time, its step by step. The design was never optimized to be done that way, so you are stuck with 2 working assembly lines and 6 non-productive. So, with what do we end? With too many lanes (that require money) that are not being used, translated into loss. Into the laptop world, this means consumption. You are running an 8-threaded core, but only using 2 threads, while the other 6 are passive (NOTE: inactive cores are NOT shut down, they are in a very low consumption state). At the end, it is a loss for you to have way too many lanes if you are not using them.

True that in the future more applications are going to use 4 threads more often. But Arrandale has that area already, with 2x2 (cores and HT). IMHO, Arrandale is more than powerful. You have 4 threads ready to be used, at fast speeds. Basically what Arrandale is, is the middle between 8 lanes at reasonable speed and 2 lanes at ultra fast speed. You get 4 lanes at high speed.

 

I don't use multi-threaded applications right now, but I do multitask at work and home. The way Bog explained it with analogies was spot on. Between background processes, multiple apps running, and wanting spare CPU power for the unexpected needs you cannot plan for a quad core has its advantages. For normal users the Dual core will again, like the core 2 series, will be overkill.

 

I was under the impression the i7 could shut down unused cores... true or false?

 

False. They go into a super-low consumption state, in which they are on, ready to take the load whenever they need to, but technically, they are never off per se. When tasking only when core for a long time, the load will even jump between cores to share it and not overtax one single part of the CPU.

 

Maybe a lil OT, but I got my Dell 1557 with the i7 720QM after waiting a long four months after my last lappy died (was using a works one in the interim). By October and Win7 launch I could wait no longer, so I dived in and got the i7 machine, which, so far, running PS CS4, I'm very pleased with.

If I could've waited the extra three months or so, would I go for a machine with an i5 instead? Maybe; it may well have suited my needs more realistically, but the luxury of waiting an extra three months on top of the four I'd already suffered just wasn't open to me! Thing is, besides not having any of the fabled heat issues with my machine, I've just done a check of the Dell UK website, and you just cannot get a Studio 1558 (the i5 one) for the price I got my spec'd up 1557 for; anything approaching my set up costs at least £100 more, even with the best e-value code available! So it seems the current economic climate has put the many people who, like me, jumped at the chance to get an i-series laptop as soon as they were available, in the quite comfortable position of having a high-performing machine for cheaper than the nearest - and less futureproof - rival, so I'm happy

 

afaik win7 is a multithreaded o/s and it will use a cpus full cpu/threading capability. so if you have multiple programs/processes working an 8 threaded i7 will help even in normal day to day tasks.
chrome for one is a multithreaded browser and should benefit from more threads. i know firefox is also movng into multithreaded browsing, im not sure though if the latest release supports it already.
javascript and flash, are already working on multithreaded versions, and afaik flash already supports it in flash player 10.
also some video player codecs such as ffmpeg are using/trying to implement multithreading to encode.decode video playback.
so we could very well see cpu's with 8 cores, or more, being used to their potential, even in day to day tasks, in the very near future.

 

Loool! Agreed, thats just why I went for the i7 720qm

 

Do you ever look at your CPU utilization? Notice how almost always it's very low? More cores won't help that. Sure, you have 100s of simultaneous threads, it's just that most of them are doing nothing. Very, very few applications outside of video encoding use more than 3-4 threads heavily, and the i5 can deal with that. Thread switching isn't a big deal when most threads are doing very little.

 

actually i do i see a 3-6 active threads while using chrome and going to video or java/flash heavy websites in tabs. i see the same when using my video and bd playback sw. i get 4 to 8 threads active when gaming and doing video editing work.
so its clearly working for me. and like i said it could be just a matter of time till more day to day tasks such as browsing adn video playback will fully utilize a cpu's maximum number of threads

 

Agreed, video playback as well as browsing/editing work will be notable on cpu usage.

 

heres a picture of my cpu using all 8 cores

 

I disagree, with the new power gate transistors, they actually do essentially shut down, mostly because that way the power that would have gone to those cores can be shunted to the operating cores in order to fuel their Turbo boost. Of course, the issue at this point becomes what one considers "shut down" and what one considers a super-low consumption state. I think we can both probably agree that what I would consider to be "shut down" and what you would consider to be a "super-low consumption state" is lower than what the old C2Qs or C2Ds would idle their cores at, though.

 

I agree with you Judicator. I mean a non shut down, as it is not actually constantly on 0% load, but as a 0-1% usage, going up and down, depending on what you are doing. But you could consider it as a shut down, as it is not working and powering the TB on the others.

Definitively the C2x could not do this.

 

And that's what consumers like I look for. Too bad my cooling is untested with the 920XM,

 

Yes! Finally, someone who agrees that using a Pentium M in the second decade is not crazy talk, i still use a ThinkPad T43 with a Pentium M 760 and the power is just fine for most everything, it can even stream 720p over the internet, connected to a TV, smoothly, still alot better than most netbooks we have nowadays.

 

Haha, same here!! I use my comp for everything. I'm getting a new 17'' for fun, but I think I'm keeping my ThinkPad beast as my carry-around all-purpose for as long as it lasts.