Intel Corp. shares fell to a three-year low Friday after No. 1 personal computer maker Dell Inc. said it would begin using chips from smaller Intel rival Advanced Micro Devices Inc., whose shares surged.

Dell said that for the first time in more than two decades, Intel will no longer be its sole provider of computer microprocessors, the brains that run computers.

Dell said late Thursday that it will use AMD’s Opteron microprocessors in some high-end corporate server machines. That announcement sealed a long-running on-again, off-again courtship between the two companies.