User sucessfully replaces Apple iMac’s stock 1.83 GHz processor with 2GHz Intel Core Duo

A writer for the Japanese print mag “Macfan” is reporting that he bought a Core Duo 2 GHz CPU and installed it in his iMac Core Duo 17-inch — replacing the iMac’s stock 1.83 GHz Core Duo.

“The machine booted flawlessly and system information displayed the right 2 GHz frequency,” Hardmac reports. “A CPU frequency is related to two parameters, the bus frequency, and the multiplying coefficient of the CPU. On G3s and G4s, the easier way for overclocking was to modify the multiplying coefficient. Yet to prevent such a manipulation, Intel, and then AMD, locked those coefficient setttings directly inside the CPUs. That’s why overclocking of X86 CPUs require modifying the system bus frequency. So, as any other CPUs, the Core Duo have a locked coefficient. The system bus of those machines is at 166MHz (x4 = the announced 667). The original CPU had a coefficient locked to 11. The 2 GHz one is locked at 12. That’s why the simple fact of changing it allowed to reach the right, reference frequency, without any further modification. The real good news is that Apple didn’t find useful to add a lock inside the EFI in order to prevent a potential upgrade.”

Full article here.

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23 Comments

  1. Waaaait a second. How’s this possible? It’s not just the CPU, but the whole motherboard that should be different between the two models. Plus of course the OS would be compiled for PPC, not Intel.

    I’m not sure I buy this …. Or maybe he just meant it booted to some hardware-level state, not the full OS?

    Hmmmm…..

  2. RE: Apple did not lock the EFI
    Perhaps they will on future models, I hope not.

    RE: 2.0GHz
    Was it heat, supply/availabilty or price that kept the 2.0GHz out of the new iMac?

  3. I’ve always been annoyed that Apple has a habit of kicking the 20″ up a notch. I wish the speeds were the same and the screen was the difference. Sometimes it’s not price, it’s SPACE it’s sitting in, and I’d like the fastest 17″ Apple can make. I can’t fit the 20″!

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