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Strange i5 750 behavior - Is this normal?

Last response: in Overclocking
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February 16, 2011 11:18:58 PM

I am a noob to overclocking, and have decided to mildly overclock my system to get a bit better performance with FSX. Upon getting everything ready, I noticed some numbers that make absolutely no sense to me. Details:

i5 750
Gigabyte GA-P55A-UD3
G.SKILL 2 x 2GB DDR3 1333
Ambient temp is 19 C

CPUZ & Core Temp

With Turbo Boost set to AUTO or ENABLED (makes no difference) in BIOS and at IDLE -
Core speed - 3.18mhz
Multiplier x24
Core voltage .896 V
26-30 C

With Turbo Boost set to AUTO or ENABLED, running PRIME 95 @ about 4 minutes -
Core speed - 2.793mhz
Multiplier x21
Core voltage 1.2 V
78-80 C (I quit at 80C)

With Turbo Boost DISABLED at IDLE -
Core speed - 2.664mhz
Multiplier x20
Core voltage .864 V
25 C

Shouldn't the core speed at idle be approx 2.66mhz, and under max load approx 3.2mhz? It seems like it's running backwards, and the Turbo Boost is running at idle. I have C1, C3/C6 etc all set to enable. I did not adjust or change any settings in the BIOS except switching the Turbo Boost on/off.

Why is the Turbo Boost running at idle, and why does the CPU speed lower at max load?
a b K Overclocking
February 17, 2011 12:21:19 AM

First off those temps are too high. 78C-80C is way too high for a i5-750, you need to get those temps down. What heatsink did you use and how did you install it?

Secondly, most of those numbers do seem off, although some of them make sense. Looking at the load numbers it looks like turbo boost senses that temps are too high and downclocks the CPU as a result. Also, at idle, is it possible that there is a background task that is running that could be running on only one core such that turbo boost would kick in. I mention that because a 24X multiplier is consistent with a single active core receiving a full boost. Check task manager if you haven't already to check CPU utilization at idle to see if one CPU happens to be occupied.

I have to admit though that those numbers do seem off.

Edit: turbo boost doesn't work exactly the way you described. Turbo boost doesn't increase clock speed simply when the CPU is under load. It increases clock speed when the CPU is under load AND when there is thermal headroom. Typically thermal headroom is available when one or more cores are not running at full speed and the extra thermal headroom the idle cores open up is what turbo boost exploits in order to raise the clock speed of the active cores. When you run prime95 on all 4 cores there isn't enough headroom to increase clock speed, but if you run it on only 1 or 2 cores you will see it kick in and raise clock speed on the active cores.
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February 17, 2011 2:11:02 AM

jprahman - I'm running stock cooling, but since I'm not overclocking yet, I'm not sure why temps are high. BIOS has been flashed to most recent version.
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a b K Overclocking
February 17, 2011 2:15:14 AM

Have you checked that the stock heatsink is mounted securely? Those temps seem way to high even with a stock heatsink. Also, what case do you have and what kind of fans are you running?
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a c 100 K Overclocking
February 17, 2011 2:23:19 PM

I think that heatsink isn't on right.

Other than that, the only wierd thing is that at idle it should only be at 9x multiplier. There must be a background task running.
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February 18, 2011 12:26:46 AM

Hehe hate to be a troll, but doesn't having your CPU @ 2.66MHz count as extreme underclocking?
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February 18, 2011 2:29:36 AM

I have a Cooler Master Gladiator 600 case with one 120mm front fan and one 140mm top fan. I will check the stock cooler tomorrow and make sure it's properly connected.
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a c 183 K Overclocking
February 18, 2011 2:38:16 AM

sargent d said:
I have a Cooler Master Gladiator 600 case with one 120mm front fan and one 140mm top fan. I will check the stock cooler tomorrow and make sure it's properly connected.

Another 120mm in the rear exhaust mount will do wonders for airflow.
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February 18, 2011 2:41:08 AM

Is it possible that CPU-Z is giving me incorrect readings? Right now at idle w Turbo on:

CPU-Z:
3057.5 MHz
x23 multiplier

Core Temp:
1395.90 MHz
x10.5 multiplier

??

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a c 100 K Overclocking
February 18, 2011 2:48:58 AM

PudgyChicken said:
Hehe hate to be a troll, but doesn't having your CPU @ 2.66MHz count as extreme underclocking?


No, that would be stock speed.

OP: You should consider downloading the Intel Turbo Boost gadget for windows. CPUZ definitely seems wrong, like it's not refreshing. You could also try Real Temp, it's been good for me.
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February 18, 2011 5:34:52 PM

wolfram23 said:
No, that would be stock speed.


Dunno man, last time I checked stock speed was 2.66 GHz not 2.66 MHz lol. Jokes never work when you have to explain them to people...
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a c 100 K Overclocking
February 18, 2011 6:26:13 PM

PudgyChicken said:
Dunno man, last time I checked stock speed was 2.66 GHz not 2.66 MHz lol. Jokes never work when you have to explain them to people...


Ohhhh... duhhh.. :na: 
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a b K Overclocking
February 18, 2011 6:32:37 PM

Late nights suck. :) 
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February 19, 2011 1:28:30 AM

PudgyChicken said:
Dunno man, last time I checked stock speed was 2.66 GHz not 2.66 MHz lol. Jokes never work when you have to explain them to people...


Oops! Sorry about that. Check this out though - all running at the same time:

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a c 100 K Overclocking
February 19, 2011 1:55:17 AM

I have CPUZ version 1.55 right now and it's working fine for me. It could be some issue with the newer version you're using, perhaps.
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February 19, 2011 3:30:48 AM

I found someone else with the same issue. Looks like it's the Turbo -

"By default, the i5 750 is 2.67GHz. However, what you're looking at is Turbo Boost. If all 4 cores are running, then the cpu(s) will run at 2.67GHz. If only 1 core is needed by an application, it will run at 3.2GHz. If 2 or 3 cores are needed, it will run anywhere between 2.8-3.2GHz."
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a b K Overclocking
February 19, 2011 1:33:20 PM

Quote:
Intel Core i5 750 TURBO BOOST

(Stock, 20x): 2.66GHz
(4 Cores Active, 21x): 2.80GHz
(3 Cores Active, 21x): 2.80GHz
(2 Cores Active, 24x): 3.20GHz
(1 Core Active, 24x): 3.20GHz


All 4 cores are active when running Prime95 and therefore operates at lower frequency.
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