Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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Why does CPU run at half speed after SSD upgrade?

My iMac 10,1 Late 2009 3,06 Core2Duo returns almost exactly half the score it should (I have another machine, same specs at hand for reference).

Software solutions tried so far:

- reset PRAM

-reset SMC

- tried two different startup drives

- used one of these on the second machine, results there ok

- eliminated all Startup apps

Hardware changes. I replaced the optical drive with a Samsung 1 TB SSD EVO 840. So I still have the original HDD in the machine.

What could cause the CPU to throttle? Can a defective CPU run, albeit slowly?

Any other hardware problems which could cause this behavior?


Answered! View the answer I have this problem too

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You might get better performance if your firmware is up to date. Follow this Apple T/N: EFI and SMC firmware updates for Intel-based Macs.

Otherwise, you're hitting a known issue with this series. The optical drive SATA port is only SATA I (1.5 Gb/s) unlike the HD's SATA port which is SATA II (3.0 Gb/s). The problem is the Platform Controller Hub chip used in this system.

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Thanks, I already tried the updater, doesn't run, because my system already has the current firmware. SSD speeds are decent, I know that disc performance on this port is not ideal but ca. 200-250 MB read write which I'm getting now is ok for me, if only I could fix the slow CPU...


Are you sure the CPU is being throttled, not the fact the data stream to/from the SSD is not as fast as the HD?


You could try checking the thermal sensors as the CPU can run at a slower rate when the system is over heating. Lets give this app a try: Temperature Gauge Pro. Let us know if you see a problem here.


Well, I've tried this, temp readings are normal. I think I can rule out a software defect now. Seems CPU. I'll post another question about replacements. Thanks a lot your site is GREAT!


I don't think you have a CPU issue here. If you did you would have a dead system Vs one running slowly after adding in a SSD.


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its easy if your fans after install ssd its working like a grazy and dont conect the sensor thermal of lcd its a small cable.sorry for my bad engilsh.

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Well almost ...

In this case the original HD is still installed with the thermal sensor enabled on it. The OP swapped out the optical drive for the SSD using the dual drive kit.

If the OP had swapped out the HD for a SSD then your on the right track but this is the better solution: OWC In-line Digital Thermal Sensor for iMac 2009-2010 Hard Drive Upgrade.


yes if the change is hhd with ssd.but in this case with optical drive its the thermal sensor of lcd.


Please review the IFIXIT guide here: Installing iMac Intel 21.5" EMC 2308 Dual Hard Drive. As you can see the optical drive thermal sensor is independent of the drive its self. While not well written it does state in the last step to reconnect the cable.

The optical drive sensor is one of many sensors within the system SMC series uses. There is a different thermal sensor within the LCD unit. You may want to review the Apple service manual and or schematic for the system which shows all of the thermal sensors or you can download this app: TG Pro while I do recommend buying the full version, you'll find the trail version ID's all of the thermal sensors within your system quite nicely.


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