Which is better and why?

[Legobumb]

I did read the "Quad Core or Dual Core? Which one do I pick?" thread a little bit, but it doesn't answer my question.

Why is a quad core better than a dual core other than the fact that it has more cores? & At what threshold does a dual core become better than a quad core? What I mean by this second question is, would a Core 2 Duo 2.8GHz be better than a 2.33GHz Core 2 Quad, or would the Core 2 Duo 2.8GHz be better than the 2GHz Core 2 Quad?

Also, could someone explain to me, the difference between the different caches (L1, L2, L3 etc) and how they are different from the clock rate (I believe it's the clock rate; that hertz number, if it's not).

 

[CurseTheSky]

You can only decide if a dual core or quad core is better based on what you use your computer for, and how long you plan to keep it in service.

In the simplest terms, processor cores do the computations that make your computer work. Every time you open a program, execute a command (rename a file, create a document, etc.) or even type / move the mouse, the operating system sends a set of tasks (computations, better known as instructions), to the processor to be resolved. Generally speaking, the more cores there are to make computations, the faster a long list of instructions can be completed. Think of the classic supermarket example - with only one cashier, you'd be standing in line all day; with multiple cashiers, the line can be broken up somewhat evenly to get people checked out in a relatively decent amount of time. The more cashiers (cores) there are available, the less time you have to wait.

Unfortunately it isn't quite that simple. While a multi-core processor is more than happy to complete tasks on any and all of it's cores, the programs that create and send the instructions must be designed to target more than one core. Programs that make use of more than one processor core are considered to be multi-threaded (since a "thread" is a chain of execution instructions; multiple threads mean multiple chains, and thus a each thread can go to a different core and be executed in parallel with other threads). Though multi-threaded applications are becoming more common, many still only make use of one or two cores. Generally, only very CPU-intensive applications (video encoding, 3D rendering, etc.) make use of four or more cores at this point in time. Now that multi-core processors becoming more common, that trend in slowly changing. In the future, applications will hopefully make use of as any number of cores available.

So, now that all of that has been said, you need to decide what you use your computer for, and how "future-proof" you want it to be. Unfortunately, there is no magic number in which clock speed beats core count (though if the difference was immense, I'd certainly choose one over the other - for example, a 5.0GHz dual core vs. a 2.0GHz quad core or a 3.0GHz dual core vs. a 2.0GHz 16-core processor). Applications that are single or dual threaded (such as many games and office applications) will make better use of the additional clock speed on a dual core, while more multi-threaded applications will run faster on quad cores.

In summary, here are some benefits to choosing either a dual core or quad core. Read the advice from others and decide from there.

Dual Core
- generally higher clock speed, more performance in single threaded applications (such as many games)
- generally cheaper
- dissipates less heat
- uses less power

Quad Core
- better performance in applications that support many threads (video encoding, 3D rendering, etc.)
- more "future-proof" as applications and games become more multi-threaded
- only negligibly more expensive than dual cores considering the possible added benefits
- can be overclocked to achieve the clock speed of similarly priced dual cores

Now that that's out of the way, cache is a bank of memory located on the processor outside of the cores. If you look at a die-shot of a processor (such as this one: http://www.hardwarezone.com.au/img/data/articles/2008/2537/Phenom-Die-shot_sm.jpg), you can physically see the different areas, some of which are cores and some of which are cache, data paths, etc. In that picture, I believe the cache is the blocky areas located near the in the center-left and center-right, though I'm no expert and could certainly be wrong.

Sets of instructions, such as the threads (chains) I talked about previously, need to be "loaded" into the processor's cache before they can be executed. Cache is blazing fast (and extremely expensive) compared to normal system memory, and a processor spends a considerable amount of time fetching instructions from system memory and placing them in cache before executing (modern processors generally grab several extra blocks from the system memory "just in case" it's related to the instruction(s) it was told to fetch, so it can reduce the overall time spent fetching instructions; this is called pre-fetching). Since more cache means more instructions can be stored at once without needing to swap out space to fetch new instructions from system memory, a larger cache generally equates to more performance. How much more cache means more performance, and how much better will the system perform? I have no clue, honestly. I also don't fully understand the difference between L1, L2, and L3 cache, unfortunately.

Once again, I'm not an expert on cache (or processors in general), so don't take my word for gospel. There may be others here that can correct me on a few points or elaborate on some things that I left unclear. Either way, I hope this helped to explain the mystery behind processors without making your head spin. I find that going "too far" in depth is sometimes the best way to really help people understand why something is the way it is rather than just making a "quad cores are better!" blanket statement.

 

[perdomot]

If you encode video or multitask, quad is the way to go now that AMD has one for under $100.

 

[JFAMD]

Good answer. A key question on dual vs quad is software. Applications being released today are *generally* expecting more cores than less. They are assuming that the average low end processor is dual core, and the average mainstream processor is quad core.

Applications that will be released in the next 2 years will assume quad core as the low end and 6 or 8 core as mainstream/high end.

All this means is that instead of trying to figure out how to the most done per clock cycle in a single thread (optimizing around speed) you will see applications expecting to find several processors underneath and optimization around concurrency.

So if you think that over the next few years you will *generally* be running older software, then dual core might be OK. If you think that you will be upgrading to newer software, then you will probably be better off with more cores.

Also, generally speaking, the larger the software titles you use on a regular basis, the more likely that they will be optimized for more cores. Larger publishers ar doing more optimization because they generally have more programmers.

The key is to look at the applications that you are going to be running most of the time or the ones that are most important in order to determine the best processor.

Without knowing enough about this it is very difficult to express which would be best for you.

 

[aigomorla]

Hexcore is better.

Because more is always better.

Just Kidding!

I think curse gave about the best definition one can possibly give.

 

[Legobumb]

I guess a more proper question would be:

Which is better at doing what over the other? 2.8GHz 3MB L2 cache Core 2 Duo or 2.33GHz 4MB L2 cache Core 2 Quad?

 

[cbn]

It depends on how well the software scales on the additional cores.

http://en.wikipedia.org/wiki/Amdahl%27s_Law

 

[Legobumb]

So you're saying that increasing the number of cores makes very little difference on the performance of the computer?

 

[cbn]

So you're saying that increasing the number of cores makes very little difference on the performance of the computer?

Did you take a look at that graph in the link I posted?

 

[jvroig]

So you're saying that increasing the number of cores makes very little difference on the performance of the computer?

No, there's a limit to scaling (so no perfect scaling among any X number of course, and it does get worse as the number of cores increases), but saying "it makes little difference" is very inaccurate. It certainly does make a difference, but how much depends on what you use - OS and applications.

 

[nyker96]

i think to put it in simpler terms: if you do video/audio work get a quad. play games get a dual or quad with lots cache. multitasking a lot in windows, get a quad over dual.

 

[JFAMD]

Think of cores as lanes on a highway. And you need to move the contents of your house from one place to another.

There are 2 things to consider, speed and throughput. Speed is how fast you can go, throughput is how much stuff you can move. Speed becomes less relevant as you move to multi-core, it is all about throughput.

You are going to get 1 carload per trip. And your limit is how fast your car can go.

If you have no friends, it doesn't matter if there is 1 lane or 50 lanes, your total throughput is the amount that your car can carry.

If you have 3 other friends, each trip is 4X the load of 1 (more throughput).

But if you can only load 2 cars per trip, it doesn't matter if you have 2 freinds or 100.

You processor determines the speed that your car travels and how many "loads" it can handle, but your software determines how efficiently loaded each trip is.

The entire discussion should be around your software. You keep asking the wrong question. The difference between processor X and Y is completely dependent on the software underneath.

 

[Zim]

Worst topic title EVAR!

 

[Munky]

In general, the major advantage of dual cores is lower price and lower cooling requirements. If you're mostly just surfing the web and watching movies on the machine, get a dual. Not because it's better, just because you won't need a quad in that case. But for anything more stressful, like modern video games or movie encoding, get a quad or a triple-core. Just don't skimp on the L2 and/or L3 cache, because those are important in games.

 

[BD231]

If you can't figure out why four cores would be better than two, much less put it into a perspective for personal use that's actually benifitial to *ANY* cause you may have for a computer, don't get a quad Lego. If you're not in the know enough to even understand how multiple cores are utilized, there's a 99% chance you're not a power user and at best you're future proofing yourself with such an item.

A subtle nuance is the fact that games prefer more mgz to cores once you have two or more. A 4ghz dual core might do better than a 3ghz quad because the game simply isn't coded to take advantage of additional cores. However, encoding a DVD to AVI might be twice as fast on the 3ghz quad vs the 4ghz dual due to the extra computational power that the encoding app is able to utilize. It's all in the software, so I suggest you study up on the programs you're running vs asking about the hardware so you know what's best for you.

 

[CurseTheSky]

I guess a more proper question would be:

Which is better at doing what over the other? 2.8GHz 3MB L2 cache Core 2 Duo or 2.33GHz 4MB L2 cache Core 2 Quad?

See the bold "Dual Core" and "Quad Core" headings in my post above.

A dual core with a faster clocks speed will generally give better performance for any applications that aren't coded to make use of more than two cores. At the moment, that includes most games, office applications, virus scanners, IM clients, etc. (generally, games are the only things that actually NEED the extra performance). As time goes on and quad (or hex, or 8) cores become more common, many of these applications will most likely be coded to take advantage of more than 2 cores; so, depending on how long you plan to keep the computer, a dual core might not be a good investment.

A quad core with a slower clock speed will generally give better performance for any applications that make use of more than 2 cores. Examples include many synthetic benchmarks, video encoding applications, 3D rendering, etc.