回答“Is it possible replace CPU from i3 to i5 or i7?”You won't be able to go to Sandy Bridge. The i3 550/i5 650 /i7 860/870 are all socket 1156, Sandy Bridge chips (i5 2310/2400/21500, i7 2600) are all socket 1155 - that'd be a different logic board. In theory, you could start with a new 2011 version with the i5 quad core and upgrade it to the i7 sandy bridge, but that's quite the expensive upgrade to do on a machine if you don't have a reason to. The 2010 iMac's are 1156 - Pre-SandyBridge only. If someone proves that wrong, please let me know!