Memory chip maker SanDisk announced Monday it will sell a large chunk of its business to Toshiba for about $1 billion. The deal comes at a time when the market for memory chips faces severe oversupply. This is “a multiyear partnership and reflects a couple of different joint ventures,” said Ryan Donovan, a SanDisk spokesperson. “We’re restructuring the joint ventures in order to sell about 30 percent of our manufacturing capacity to Toshiba.”