National Semiconductor, the US chipmaker, and IBM, the comuter computer group, have agreed to end a semiconductor manufacturing pact, a move that will lead National to take a charge against earnings in the second quarter, ending November 29, of about $50m-$55m (£33.6m-£36.9m).

National said IBM would cease selling its Cyrix-designed microprocessor chips before the end of this year. In return, National's Cyrix unit will no longer be obliged to purchase semiconductor wafers from IBM.