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better overclocking by disabling one (or more) cores?

post #1 of 5
Thread Starter 
Hi,
I have never overclocked.
I just upgraded my PC, with an asus p8Z77-m pro, an Ati HD 7870 OC, an I5 3550 and a low profile zalman heatsink (CPU has not arrived yet).

This motherboard and CPU apparently allow for a lot of "speed stepping" of the CPU to reduce power consumption (and noise fan) when little CPU power is required.

Reading on this forum, it seems that Overclocking to 4. Ghz, is quite doable on the 3550 (i know that this CPU is not for overclocking and that 3570K is better for that purpose, thanks wink.gif .

I have found that my mobo's bios allows to disable up to three cores of the CPU.

I read recently that, given the same CPU speed, there is not a great difference in gaming performance comparing a CPU with 2 cores and a CPU with 4 or six cores (which makes me wonder why the new PS4 has 8 AMD cores...). More on this, for example on:
http://www.youtube.com/watch?v=I4PDoy-mi0A

And now the question/challenge:
how would the PC respond if I disabled one of the cores of the 3550 CPU? (or the 2500K or an XXXXK for those who have these)

More specifically, would I be able to overclock it further with one core disabled (say to 4,2 or 4,3 on the 3550, while remaning cool enough) and thus maybe get better game performance than with a 3550 with all cores enabled but at 4 Ghz?

Or, with one core disabled, and OC to 4 Ghz maybe I get the same performance and lower temps, than with all cores active at 4 Ghz?

This question is based on the assumption/hypothesis that games will gain little or no performance by having a fourth core active, but will benefit from a little OC.
Edited by despinos - 2/21/13 at 2:10am
post #2 of 5
The i5/i7 already does this for you. There is a feature called turbo. When less cores are used, the clock speed is increased. If the cores are needed, then the clock speed doesn't increase. The 3550 can be safely OCed to 3.9ghz on good mobos. My 3470 which is 100mhz lower runs at 3.8ghz @ 24/7. The non K chips can be oc'ed by 600mhz on Z77s.
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post #3 of 5
Thread Starter 
Thanks,
iwas actually a little confused, with Intels' "turbo" and "speed step" and also Asus mobo's own performance and energy "tweaks", named "TPU", "EPU"... combined with the user's ability to manually OC... so many factors that can be combined without the slightest idea of exactly what makes each, if they are redundant or which has priority over the rest.

Maybe the turbo automatic function will not work above 3.7 Ghz on the 3550. But, manually, one can OC to, say 4.1 Ghz by disabling one core and setting the multiplier to 39 and the base frecuency to...?? 103 maybe?

As I said, I'm a newbie, but I guess that manually (vs. automatic with turbo function) OCing allows to go a little further on this CPU :-)

In the end, I'll probably leave it to the automatic turbo feature.
Edited by despinos - 2/21/13 at 3:05am
post #4 of 5
Disabling cores does not automaticly grant you extra oc-headroom (not a lot atleast). It is used mainly to do extreme kamikaze-runs where they try to get the highest frequency possible. Some cores are more stable than others, and it's these cores overclockers want to use when they go for crazy high speeds. For general use, it is not worth disabling cores just to *maybe* get a 50-100mhz clockspeed increase.
post #5 of 5
Disabling cores can allow the remaining cores to OC significantly higher, in some cases.

If you are thermally limited, disabling cores will often provide a huge boost. Also, you lower the load on the SA//Uncore/IMC and L3 cache. Additionally, some cores are just weaker than others, so the few you use, the better the chance that the remainder are stronger cores.

Of course this will only benefit lightly threaded tasks. Rarely is disabling cores to get a modest clock speed boost going to be worthwhile for anything well threaded.

Anyway, the i5 3550 is a locked part and even at maximum OC, should not be reaching thermal or electrical limits (even with a cheap board and cooling), so it's extremely unlikely that disabling one or more cores would do anything at all to maximum viable OC.
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CPUMotherboardGraphicsRAM
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CPUMotherboardGraphicsRAM
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