Mullard 100 kcs circuit block. FF1 B8 920 00 (red) x 4 on printed circuit board, 1965
Made by the British company Mullard Ltd., these devices are complete electronic circuits, consisting of components sealed into boxes, which carry out specific logical and data-control functions. Circuit blocks were the first commercially available 'potted circuits' whose operation did not need to be understood in order to be used in an electrical system. The use of circuit blocks and, later, integrated circuits has led to standardisation, miniaturisation and modularity of electronic system design.