Analogue computer. These machines were the precursor of modern digital computers. This is an EAI (Electronics Associates Incorporated) Pace 231-R computer, a US model produced in 1961. It worked by using electrical circuits known as operational amplifiers. This model model had 20 such amplifiers. Cables were used to make connections on the 3450-socket (75x46), colour-coded patch panel (centre). This computer model was used in science and engineering projects in the aerospace, car and nuclear industries.