Being a Mac, I knew that simply searching for "apple imac" would return the apple store as the top hit. I clicked www.apple.com/imac. Scrolling down a bit I see "New Processor architecture"
Clicking that I read that available are quad-core Intel Core i5 and Core i7. To double check, I click a button to take me to where I can configure my own if I wanted to buy one and see that the quad-core Intel Core i7 is the most powerful processor.