The semiconductor disk on which microprocessors are fabricated. Many processors will usually be fabricated on a single piece of silicon, and in production are often tested in situ, before the wafer is cut into individual Dies for encapsulation into packages. The size or diameter of wafers used in fabrication has steadily increased and a higher diameter is considered both an indication of the sophistication of a Fab or Foundry, and raise its efficiency in terms of cost – early fabs were 4 inch/10 cm, then 8 inch/20 cm, high end fabs are at the time of writing 12 inch/30cm/300mm.