Intel Corp. and Advanced Micro Devices Inc., archrivals for decades, are teaming up to thwart a common competitor, Nvidia Corp.

Intel planned to announce Monday a laptop-computer chip that combines an Intel processor and an AMD graphics unit, according to a person familiar with the matter. The chip is intended for laptops that are thin and lightweight but powerful enough to run high-end videogames—attributes that lately have been driving sales in an otherwise waning market for personal computers.

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