Page "Central processing unit" Paragraph 12

During this period, a method of manufacturing many interconnected transistors in a compact space was developed.

The integrated circuit ( IC ) allowed a large number of transistors to be manufactured on a single semiconductor-based die, or " chip.

" At first only very basic non-specialized digital circuits such as NOR gates were miniaturized into ICs.

CPUs based upon these " building block " ICs are generally referred to as " small-scale integration " ( SSI ) devices.

SSI ICs, such as the ones used in the Apollo guidance computer, usually contained up to a few score transistors.

To build an entire CPU out of SSI ICs required thousands of individual chips, but still consumed much less space and power than earlier discrete transistor designs.

As microelectronic technology advanced, an increasing number of transistors were placed on ICs, thus decreasing the quantity of individual ICs needed for a complete CPU.

MSI and LSI ( medium-and large-scale integration ) ICs increased transistor counts to hundreds, and then thousands.