I am thinking of upgrading the current Core 2 Duo 3.33GHz to Quadcore

One problem with this is the 21.5" iMac has a 1066MHz system bus, and the better C2D processors are 1333MHz bus speeds. If you stuck a Core 2 Quad chip in the iMac, it would probably revert down to the 1066MHz bus speed, which would significantly reduce the overall clock speed of the new processor. But, if it did work at least you would have quad cores.

Well... since you're obviously willing to scrap the warranty anyway, I'd try to overclock the 21.5's E8600 (the 3.33 core 2 processor) first before I'd try to swap the chip (which could be both a heating and a compatibility issue). That particular Core 2 is the badest Core 2 Dual ever made. PC users have overclocked it to 4.00 ghz, 5 ghz and beyond. The iMac is a tight unit, but you might be able to safely overclock it through software by a few percentage points and see how it goes. If you are mechanically inclined, you might even find a way to improve the cooling system in the iMac.

I have a iMac 21,5 to and I'm also interested upgrading my E7600 to a Q9550s if this is possible.

Since the Q9550s also uses 65W just like the E7600/E8600 and the bus speed is the same as the E8600 (1333MHz) which is a upgrade I think it might be possible. The only question is: "Will the firmware detect the Quad-core properly?"

I will certainly wait until my warranty is expired, even if nobody have tried it, I certainly will. Of course I love to see anyone doing this, then I really know if it's compatible or not so I will have it clear for myself.

That is something I doubted about to, but the 3,33GHz E8600 model is a 1333MHz, just like Q9550s. I think the firmware of the iMac will change the clock ratio for the processor to let it run at original speed.

E7600 = 1066Mhz > 3.06Ghz

E8600 = 1333Mhz > 3.33Ghz

Let's say the Q9550s is in my opinion the most equal to the E8600 in specs, If this would work it will be a nice upgrade!

If the iMac can do a 1333 FSB, then I would think a Core 2 Quad would actually work. Assuming it is similar architecture as the Core 2 Duo being replaced. I read about someone trying this swap elsewhere, and they had no luck (no boot), but they used one generation older Core 2 Quad, which would have a higher thermal loading, and the chance of it being compatible was not that high in the first place.

I have heard of someone replace the C2D with a C2Q, whether or not it was a Q9550 (most likely possibility) i have no idea- they gave no extra information other than the fact Apple recognises the Quad Core as a Xeon in the "About This Mac". It's always worth a try- especially now with the Processors being much cheaper than the new iMac i7 Processor

Good night, I have an iMac 2009 core 2 duo 3.06 E7600

socket 775

TDP 65w

1066mhz

Note: This iMac also came with a 3.33 core 2 duo processor E8600 socket 775 TDP 65w 1333mhz.

I made some memory changes to 12giga SSD 250giga, the machine has improved a lot.

I recently purchased a Q8400s quad core 2 processor

socket 775

TDP 65w

1333mhz

It doesn't justify not working, but it doesn't even turn on the screen, I reset the vram, I disabled the EFI (operating system) and nothing.

Can someone help me.