Question: Core 2 Duo vs. Hyper Threading

[jcgnu]

Hi everyone. I have a question of which I should know the answer, since I'm a computer engineer, but anyway... I currently have a laptop with a 3.4 GHz Pentium 4 w/HT processor. Today I bought a Mac that comes with a 2.4 GHz Core 2 Duo processor. Of course, both computers have 2 processors each.

I've always wondered if those 3.4 GHz are per processor or altogether. The same for the 2.4 GHz.

Because if in both cases it works the same way (either one), that would mean that I'm getting a slower computer that one that I bought 4 years ago. Still, a better computer for many reasons, but slower. Furthermore, that would mean that I currently have a laptop that's even faster than a lot of PC's (even Mac's) out there. It sounds kinda stupid, plus my computer is running really slow, but still, I want to know.

Anyway, I'd really appreciated it if someone could help me answer my little question. Also, for those quad-core, 8-core, etc, how does it work for them. Is the number of GHz per processor (or core, or whatever) or is it the speed for all of them together.

Thanks,

 

[cohibadad]

it's per core. HT isn't multicore so it isn't equivalent to C2D. GHz doesn't equate to faster. P4<<C2D

 

[Andrew275]

HT does not equate to multicore, and aside from that the C2D is much faster than the P4 clock-for-clock. Check this site out:

System Shootouts

It hasn't been updated in a while, but according to that site, a 2 GHz Core Duo would be roughly equivalent to a 4.8 GHz Pentium 4. Also note that I said Core Duo and not Core 2 Duo. The C2D would be even faster.

Bottom line, the 2.4 GHz C2D will be a huge upgrade from the 3.4 GHz P4.

The GHz in a multicore system is the per-core clock speed. In other words, you effectively have two processors, each running at 2.4 GHz.

 

[jciapara]

Dual Core

Basically multi-core means 2 or more cores in one IC (die) all of them typically running with the same clock. like 2.4 Ghz each in Apple's laptop, this is better than running one Pentium 4 at 3.4 Ghz in the sense it irradiates less heat (Clock at lower speed) and with the 2 cores you can ideally do 2 instructions each cycle, thus doubling the rate at which instructions are executed (but this is not the case since instructions use more than 1 cycle and some applications aren't programmed to take advantage of multi-cores). Anyway this is a brief explanation, I'm sure someone else can elaborate more, or even correct me on something I might've said wrong. I hope it cleared some of your doubts.

 

[jcgnu]

Well, first of all thanks for your answers. On top of everything, as I suspected I'm getting a faster computer (not just in practice but in theory as well).

I totally agree that it is better to have a C2D than a P4 because the second one overheats a lot. Actually, a P4 HT wasn't supposed to be built inside a laptop, but I went for it and ended up with a superfast computer (4 years ago) that always gets reaaaaally hot, that's really noicy, and whose battery can't last 20 minutes on (not to mention that the original battery broke and the replacement is not HP, so I have to unplug the computer everytime I want to turn it on, which let into more problems, that are not worth mentioning).

Anyway. Thing is, I don't really understand what 2-cores means, versus 2-processors (like my computer). I'm sure my computer has 2 processors. I can see that in the Task Manager (in crappy Windows, of course) and if I run a little program called CPUInfo, which in fact tells me that each CPU runs at 3.4 GHz.

So, I think the question of "what's better?" has been totally clarified. I just want to fully understand and will thank you a lot for your help.

 

[queshy]

I don't even want to know the battery life on your P4 laptop!

 

[pip11]

Dual-core is essentially the same thing as dual-processor. Dual-core just means that they are both on the same chip (so only one socket is needed on the motherboard), while dual-processor implies that the computer has two separate sockets, and single-core processors in each of them. This distinction is important mainly on the hardware level, but makes no difference to the software running.

That said, your Pentium 4 HT has neither of these. It is one processor, with one core. However, it presents itself to the operating system as two cores/processors, to try and make sure that every part of the processor is being used as much as possible. Whlie it can improve performance, it is absolutely not the same thing as having two separate cores/processors. For some tasks, HT makes no difference, and could even reduce performance, because of the extra overhead from coordinating multiple threads.This article at arstechnica is an okay introduction to HT and multithreading.

 

[jcgnu]

Ohhhhh that was very clear, thanks... Problem solved! I always thought that my computer had 2 processors (since everything indicated it, like the Task Manager or the CPUInfo, which presents 2 tabs in the section "Processors"). Anyway, it's fake, it's emulated, so no 2 processors inside this baby... Another reason to be happy that I just bought a MBP.

Thanks to all

 

[eXan]

P4 is total crap when it comes to being efficient. Core 2 Duo is one if the best (the best?) at it. Even if your P4 HT had 5 GHz, it would be wasted by 2.4 Ghz Core 2 Duo's ONE core. Even better is that Core 2 Duo has 2 cores, which is basically a more efficient version of having 2 separate processors (advantages of multiple cores are: it can use 1 "pool" of cache, faster interconnection between cores, takes significantly less space physically, emits less heat, takes less power).

Hyper threading technology tricks the system to make it think it has 2 cores/processors, but in reality gains of performance in optimized tasks are about 20%.

Real dual core system can nearly (90+% in OS X) double the performance if the task can use multiple cores (most modern apps can use at least 2 cores). But even if the task cant use more than 1 core, you can still run other tasks on another core without slowing down the first task.

Hope I make sense...