Advanced Micro Devices Inc. said Chief Financial Officer Marvin Burkett resigned to join an undisclosed closely held company, leaving a company he's served for 26 years. Computer-chip maker AMD declined to say where Burkett, 56, is headed. Burkett joined AMD in 1972 and was named CFO in 1989. Richard Previte, the company's president and chief operating officer, will be acting CFO until a replacement is found. The resignation comes at a critical time for AMD in its battle against chip-market giant Intel Corp. The company has had production problems making its latest K6 microprocessors, its answer to Intel's top-selling Pentium chips that run low-cost personal computers. AMD has said it won't discuss its progress on the K6 until it reports first-quarter earnings April 7. Burkett declined to name the company. He said he is taking a position of CFO or higher in the chain of command. Shares of the Sunnyvale, Calif.-based AMD fell 13 cents to close at $22.94 on the New York Stock Exchange.