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Naive Question about GHz

R

rscott505

macrumors member
Original poster
Feb 11, 2008
59
0
I apologize in advance about this question, but I'm not that technically inclined.

In looking at the new macbook pros, I noticed that the 13 inch macbook pros have faster GHz, then the 15 inch macbook pros. I recognize that the 13 inch have dual core, and the 15 inch have quad cores, but I thought that the GHz speed was an objective figure.

So basically, can someone explain to a liberal arts major how the quad core with a slower GHz figure run faster than a dual core.

I know this question may seem dumb, but I really am technically challenged, but I would like understand this.

Thanks.
 
rscott505 said:
I apologize in advance about this question, but I'm not that technically inclined.

In looking at the new macbook pros, I noticed that the 13 inch macbook pros have faster GHz, then the 15 inch macbook pros. I recognize that the 13 inch have dual core, and the 15 inch have quad cores, but I thought that the GHz speed was an objective figure.

So basically, can someone explain to a liberal arts major how the quad core with a slower GHz figure run faster than a dual core.

I know this question may seem dumb, but I really am technically challenged, but I would like understand this.

Thanks.
Click to expand...

Actually it doesn't run faster at all, it uses the same socket and runs at lower frequency and in anything using 2 or less cores it is faster than the quad models.

However for some of the more pro applications music and video encoding, multi-threading is highly optimized and the work for a process can be divided amongst more cores.

Basically the answer is for the average user it is faster, for the gamer(new games) and movie/audio person the quad is faster.
 
The CPUs have something called Turbo Boost that dynamically increases the clock speed of the CPU based on how many cores are in use.

The 2.7GHz CPU in the 13" will run at 3.4GHz while 1 core is in use and 3.2GHz while 2 cores are in use while it is able to meet certain power and heat requirements.

The 2.3 GHz CPU in the 15/17" will run at 3.4GHz with 1 core, 3.3GHz with 2 cores, and 3.1GHz with 4 cores in use under the same requirements.
 
Think of painting a picture and the size of the brush is the speed of the CPU. And the dual cores allow you to use two brushes at once and the quad allows you to use four. When you are painting the first layer of blue for the sky, the dual brushes are put together and used at one big brush. The four slightly smaller brushes are put together, but make a bigger brush then the two brushes. Thus, they can paint the blue sky faster. It isn't exactly like this, but it gets the general idea across.
 
Intell said:
Think of painting a picture and the size of the brush is the speed of the CPU. And the dual cores allow you to use two brushes at once and the quad allows you to use four. When you are painting the first layer of blue for the sky, the dual brushes are put together and used at one big brush. The four slightly smaller brushes are put together, but make a bigger brush then the two brushes. Thus, they can paint the blue sky faster. It isn't exactly like this, but it gets the general idea across.
Click to expand...

some pictures can only be painted with one brush. Of course that is what turbo boost was invented for...

...however for the average user you really want to go with the 13" and the upgraded processor is really nice.
 
The dual core CPU with 2.7GHz has two cores running at 2.7GHz, the quad core CPU with 2.3GHz has four cores running with 2.3GHz, therefore it is at least 1.7 times faster. As the dual core supports four threads (two threads per core) and the quad core supports eight threads (two per core), the quad core is faster again, as properly programmed applications, which can take advantage of multi core CPUs and multiple threads, will perform faster with more cores and threads, even if the numerical value of the frequency is lower.
 
In very basic terms, imagine instead of computing things, you are baking cakes.

There are 2 cooks, we'll call them A and B. Cook A can make 50 cakes per hour, while Cook B can only make 40 cakes. So, even though Cook A is faster than Cook B, 2 of him can only make 100 cakes per hour (dual-core), where as four of Cook B can make 160 cakes per hour (quad-core).

Core speed is good, but with more of them, you can theoretically do more work, even if they might be a tad slower.
 
Think of it as four 2.0ghz processors compared to two 2.3ghz ones. Obviously, having double the cores outweighs any clock speed (ghz) advantage.

But this advantage is only seen in applications that can take advantage of multiple cores, if it's only going to use one of the cores, then whichever has the higher clockspeed is better. The application has to know how to "split" the task between all the cores and if it cannot, then the extra cores go wasted. This is where turbo boost comes in.

The quads are rated at 35W at peak which means all four cores running dumps out 35W of heat. So if it's only using one, reason dictates that it is going to be using much less. So, the processor boosts one of those four cores up to a higher speed which helps it maintain the speed advantage. It can boost 1, 2, 3 or even all 4 cores as long as it remains within the thermal and power consumption specifications.
 
Thanks for the answers. All of them combined help me understand this.

I will definitely use this information to help me sort through my next purchase.

Again, Thanks everyone.
 
This was very helpful to me as well. Thanks! Sounds like the upper end 13" model will work great for my needs.
 
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