Although the electronic computer belongs to this century, mechanical computing devices have existed for a very long time. The abacus was in use in the Middle East and Asia several thousand years ago. In about 1590 the Scottish Nobleman John Napier invented logarithms and an aid to multiplication called “Napier’s Bones”. These so-called bones consist of a set of rectangular rods, each marked with a number at the top and its multiples down its length; for example the rod marked “6” would have the numbers 0, 12, 18, 24, etc along its length. By aligning rods (e.g., rods 275) you could multiply 275 by another number by adding the digits in the appropriate row. This reduces the complex task of multiplication to the rather easier task of addition.  A few years later, William Oughtred invented the slide rule – a means of multiplying numbers that used sliding rules. 

During the seventeenth century major advances were made in watch making. The art of watch making helped develop the cog wheels required by the first mechanical calculators. In 1642 the French scientist Blaise Pascal designed a simple mechanical adder and subtracter using cog wheels with ten positions marked on them. One complete rotation of a wheel caused the next wheel on its left to move one position (a bit like the odometer used to record an automobile’s mileage). Pascal’s most significant contribution was the use of a ratchet device that detected a carry (i.e., a rotation of a wheel from 9 to 0) and nudged the next wheel on the left one digit. If two wheels show 58 and the right-hand wheel is rotated two positions forward, it moves to the 0 position and advances the 5 to 6 to get 60. Pascal’s calculator, the Pascaline, could perform addition only. Subtraction was possible by the adding of complements – a technique that was later adopted by digital computers. 

Wilhelm Schickard, rather than Pascal, is now generally credited with the invention of the first mechanical calculator. His device, created in 1623, was more advanced than Pascal's because it could also perform partial multiplication. Schickard died in a plague and his invention didn’t receive the recognition it merited. Such near simultaneous developments in computer hardware have been a significant feature of the history of computer hardware. 

The German mathematician Gottfried Wilhelm Leibnitz was familiar with Pascal’s work and built a mechanical calculator in 1694 that could perform addition, subtraction, multiplication and division. Later versions of Leibnitz's calculator were used until electronic computers became available in the 1940s. 

Within a few decades, mechanical computing devices advanced to the stage where they could perform addition, subtraction, multiplication and division—all the operations required by armies of clerks to calculate the trigonometric functions we mentioned earlier. 

 Pascal’s Calculator – The Pascaline 

The Industrial Revolution and Early Control Mechanisms

By 1800 the industrial revolution in Europe was well under way. Weaving was one of the first industrial processes to be mechanized. A weaving loom passes a shuttle pulling a horizontal thread to and fro between vertical threads held in a frame. By changing the color of the thread pulled by the shuttle and selecting whether the shuttle passes in front of, or behind, the vertical threads, you can weave a particular pattern. Controlling the loom manually is tedious and time-consuming. In 1801 Joseph Jacquard designed a loom that could automatically weave a predetermined pattern. The information necessary to operate the loom was stored as holes cut in cards—the presence or absence of a hole at a certain point controlled the behavior of the loom. Information was read by rods that pressed against the card and either went through a hole or were stopped by the card. Some complex patterns required as many as 10,000 cards, which were strung together in the form of a tape. The punched card contains a recipe for a pattern—or a program. 

The notion of a program appears elsewhere in the mechanical world—consider the music box that plays a tune when you open it. A clockwork mechanism rotates a drum whose surface is embedded with spikes or pins. A row of thin metal strips, the teeth of a steel comb, are located along the side of the drum but don’t quite touch the drum’s surface. As the drum rotates, a pin sticking out of the drum meets one of the strips and drags the strip along with it. Eventually, the pin rotates past the strip’s end and the strip falls back with a “twang." By tuning each strip to a suitable musical note, a tune can be played as the drum rotates. The location of the pegs on the surface of the drum determines the sequence of notes played.

Although Jacquard’s loom may seem a long way from the computer, it demonstrates that the intellectual notions of control and sequencing have existed for a very long time.