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:
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
Core voltage .896 V
With Turbo Boost set to AUTO or ENABLED, running PRIME 95 @ about 4 minutes -
Core speed - 2.793mhz
Core voltage 1.2 V
78-80 C (I quit at 80C)
With Turbo Boost DISABLED at IDLE -
Core speed - 2.664mhz
Core voltage .864 V
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?
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.
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."