Dadda Multiplier Named an IEEE Milestone

The 1965 invention significantly reduced the time it took processors to do arithmetic

11 October 2016

In the mid-1960s, ever-higher-speed arithmetic circuits were needed to keep up with quickly evolving computer processors. IEEE Fellow Luigi Dadda [above], an electrical engineering professor at the Polytechnic University of Milan, came up with a design in 1965 for an arithmetic circuit that could multiply binary numbers using fewer steps than ever before. It became known as the Dadda multiplier.

The breakthrough was recognized last month with an IEEE Milestone. Administered by the IEEE History Center and supported by donors, the IEEE Milestone program recognizes outstanding technical developments around the world.


A binary multiplier is an electronic circuit that multiplies the binary numbers that hold bits of information. The Dadda multiplier is unique in that it defers and distributes those bits in a way that’s simpler for the circuit to process. It reduces the number of operations the circuit must perform, thus speeding up its operation. It also reduces the number of logic gates, the elementary building blocks of a circuit needed to do the math.

Into the mid-1960s, arithmetic circuits were mounted on circuit boards, with long wires running between them. That configuration took up a lot of space inside a computer and slowed its processing speed. Dadda’s design reduced the number of circuit boards and led to fewer and shorter connections between chips.

The Dadda scheme for parallel multipliers was published in 1965 in the journal Alta Frequenza (High Frequency). Also known as the Dadda tree, his design has become one of the two recognized structures for a basic arithmetic circuit, along with a similar one developed in 1964 by computer pioneer Chris Wallace. Dadda trees and Wallace trees represent the two standard parallel multiplier schemes still illustrated in modern university textbooks on computer arithmetic.

Dadda was elevated to IEEE Fellow in 2000 “for contributions in the field of arithmetic architectures for computers and DSP [digital signal processing] systems.” He was a founding member of the Italian Association for Computing and served as its president from 1967 to 1970. He died on 26 October 2012 at the age of 89.


Dadda’s multiplier was honored on 26 September with a ceremony at the Polytechnic University of Milan. A plaque mounted near the entrance of the university’s main hall reads:

Luigi Dadda published the first description of the optimized scheme, subsequently called a Dadda Tree, for a digital circuit to compute the multiplication of unsigned fixed-point numbers in binary arithmetic. This circuit allowed the arithmetic units of microprocessor-based computers to execute complex arithmetic operations with a performance/cost ratio unequaled at that time. His research and teaching pioneered computer engineering in Italy.

This article was written with assistance from the IEEE History Center, which is partially funded by donations to the IEEE Foundation.

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