Which Intel core i7 CPUs can I use in my iMac?

If you have an iMac with a removable CPU (there are very few) you would need to stay with processor versions Apple sold or offered as upgrades to your line of machine. If you use other CPUs you'll have firmware problems.

Economically it is much more feasible to just sell your old box and buy one that meets your requirements... and... if you want to do lots of upgrading a MacPro is a much better platform to start with than an iMac.

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