➀ Hynix has started mass production of the world's first 321-layer NAND with 1Tb capacity; ➁ The 321-layer device offers a 12% improvement in write time and a 13% improvement in read time compared to the 238-layer device; ➂ Hynix has adopted the '3 plugs' process technology and a low-stress material for stacking more than 300 layers.