Selecting Processor - About to Order

The duo has a faster FSB and a faster CPU clock but only two cores.  The quad has four cores that operate more slowly.  So the real question is:  Do you actually need the third and fourth cores?  If not, the duo will be faster.

 

My rough benchmarks have shown (using the Q6600) that you lose roughly 10% of each cores performance as another core is utilized.  This means that four cores performs roughly like 2.8 cores (4*.7=2.8).   Total performance is roughly 2.8*2.4GHz or 6.7 GHz equivalent.

 

Applying the same rule to the dual core, you get 2*.9*3.16=5.7 GHz max equivalent performance.

 

So the quad is only a bit faster when you can load all 4 cores, but will be slower with only one or two cores loaded.  The quad is also older technology, with a slower FSB, etc.  Hence, most people would probably find the dual core is the better overall choice.

 

I have a Q6600 and like it because I can run 3 CPU intensive software tests in parallel and still have another core that keeps the machine responsive for watching HDTV or doing some other task at the same time.  But I don't think I am typical.

 

Peter

Hi Peter,

 

Thanks for your response, very informative.  I didnt realise each processor as such would run individually and separate for different tasks (if I understand your explanation right anyway). But yes for my needs it will probably be great and I appreciate you explaining in detail

 

Cheers

What I get for reading posts after 5 AM. Was reading a debate over Vista & Windows XP, 32 bit vs. 64 bit of each. Guess the posting on quad core was WinXP 64 bit to use quad cores effectively; but I don't know so won't comment further.

 

Vista does support dual and quad cores. 64 bit Vista does offer more than just support for 4 GB of RAM.

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@Xelkos wrote:
I read on support sites that a 64 bit OS is needed to unlock/use all four cores.

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That is wrong.  A 64-bit OS is needed to access more than 4G of memory (technically there are other ways, but 64-bits is the "right" way).

 

I have a Q6600 with XP Home.  It can use all four cores no problem.   I can run 4 CPU intensive apps at once and still have a responsive machine.  One CPU intensive app shows the CPU utilization at only 25%.

 

Peter

Peter,

 

Do you know what sets core affinities?  

 

That is, we can choose core affinities manually (and there is software that will do this), but how does the system allocated the tasks? 

 

For example, if one core is 30% utilized and a new process is initiated that would take another 30% of one core - will this task be assigned to the already active core or automatically assigned to another?  How is this determined by the system.

 

I am intrigued by your comment that you multi-task and that each task keeps a defined core busy.  I haven't seen such a clear core delineation of tasks, but haven't actively tried to hunt this down either. 

 

(My system is currently busily working away at spectrum analysis and repair of a large 24-bit 96kHz sound recording at the moment - all four cores are showing activity, which is normal for this application).

I stated it more simply than the reality.  I don't claim to be an expert on this subject (how Windows assigns tasks to cores/processors), but I can tell you what I have seen.

 

Windows automatically assigns the tasks to the cores.  Even a single thread will run on multiple cores.  Right now I am running a single CPU intensive app, and I see a total of 26% CPU utilization (one core effectively used), but the load is spread over several cores.  One core is loaded at about 70% (of a core max load, not the machine max load) and another at about 20% with the other two cores showing about 5% each. You can see the load on each core going up and down, but the total load is constant.

 

If I run the same exact job a gain, I see a similar yet different pattern of loading.  The load is more evenly split between the same two cores (2 and 4) that were doing the bulk of the work before.

 

Peter

 

 

This is what I have seen as well. Certain cores seem to be favored, but the work is spread around. Fascinating stuff.

Thanks!