Feb 3 : Western Digital said on Tuesday its board has approved $4 billion more for share repurchases, as demand for its memory chips used in artificial intelligence servers surges. Its shares rose about 5 per cent in premarket trading, adding to a 57 per cent jump this year. The shares had more than tripled in value last year. A global shortage of memory chips has intensified competition among AI and consumer electronics companies for limited supplies, driving up prices and extending lead times