Early calculating devices

The invention of logarithms quickly led to the development of instruments based on a logarithmic scale. Most notable among these was the slide rule, versions of which first appeared around 1630 and were widely used for over three hundred years until the advent of the pocket calculator.
The first mechanical calculating machines appeared in the 17th century. In 1623 an early machine was described by William Schickard in letters to Johannes Kepler, but it was never built. Later calculating machines were constructed by Blaise Pascal and Gottfried Wilhelm Leibniz. Pascal’s machine (the Pascaline) was operated by cogged wheels and could add and subtract numbers, while Leibniz’s calculating machine could also multiply and divide. Neither machine worked efficiently in practice.
[Germany 1973; Romania 1957; São Tomé and Príncipe 2008]

Al-Khwarizmi

Several mathematical words date from the Islamic period. The word algorithm (a routine step-by-step procedure for solving a problem) derives from the name of the Persian mathematician Muhammad ibn Musa (al-)Khwarizmi (c.780–850), who lived in Baghdad and wrote influential works on arithmetic and algebra.
 His Arithmetic was important for introducing the Hindu decimal place-value system to the Islamic world, and in medieval Europe the word algorism later came to mean arithmetic. The title of his algebra book, Kitab al-jabr wal-muqabala gives us the term algebra, the word al-jabr referring to the operation of transposing a term from one side of an algebraic equation to the other.
 [Russia 1983; São Tomé and Príncipe 2008]