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I want to perform a cheap CPU upgrade on an old Socket AM2 motherboard. I currently have an Athlon 64 X2, and want to upgrade to a quad-core AMD Phenom. IIUC, Socket AM2+ CPUs are backwards compatible with Socket AM2 motherboards. However, my motherboard (an ABit KN9) does not have a BIOS upgrade available to support this and is not officially compatible with any AM2+ CPUs.

At a technical level, what does the BIOS have to do with supporting specific CPU makes/models? What would be the likely consequences of installing an AM2+ CPU on this motherboard? Would the computer likely:

  • Not even POST
  • POST but not boot
  • Boot but be lacking some important features
  • Work with a few purely cosmetic issues

or something else?

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up vote 2 down vote accepted

In the one instance I've (accidently) tried to put an AM2+ into an AM2 board (some ASUS) it didn't POST. Some head scratching, manual reading and a BIOS upgrade later it Just Worked (tm).

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