Long-term NAND flash partners Toshiba and SanDisk plan to extend their collaboration to the development of rewritable 3D memory, EE Times reported. Previously, the two companies have separately developed 3D memory to no avail. This time the two companies will cross-license 3D-related technologies and to jointly conduct R&D. It is estimated that it will take three to four years for Toshiba and SanDisk to develop 3D memory chips capable of trumping NAND flash. At present, the two companies' main shipment consists of 43nm NAND devices, while development of three-bit-per-cell technology is underway.