The computer processor was made of small-scale integration DTL monolithic integrated circuits.

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

Now known retrospectively as small-scale integration (SSI), improvements in technique led to devices with hundreds of logic gates, known as medium-scale integration (MSI).

People building high-speed computers wanted them to be fast, so in the 1970s they built the CPUs from small-scale integration (SSI) and medium-scale integration (MSI) 7400 series TTL gates.