A calculator is generally defined as (1) any small handheld device that automatically performs arithmetic operations, certain mathematical functions, simple text editing, or elementary programming, or (2) a software program on a computer that simulates a "real" handheld calculator; for example, both Apple's Mac OS and Microsoft's Windows operating systems contain a simple desktop calculator program that allows a computer user to perform simple mathematical calculations.
While the calculator is a relatively modern invention, various simple calculating machines able to perform addition and subtraction have existed for centuries. The abacus, a memory-helping device rather than a true calculating device, is an instrument for carrying out simple arithmetic operations. It was possibly first used around 3000 B.C. in Babylonia. This device allowed users to make computations using a system of sliding beads arranged on a rack. The first attempt to design a calculating machine was probably made by Leonardo da Vinci (1452-1519). In 1622 English mathematician William Oughtred (1574-1660) invented another calculating instrument called the slide rule. Engineers and scientists regularly used slide rules until the introduction of the calculator in the 1960s.
The invention of the first mechanical calculating machine for the addition of numbers is commonly credited to the French mathematician Blaise Pascal (1623-1662). Modern calculators are generally considered descendants of the machine devised by Pascal. In 1642 Pascal created a numerical wheel calculator, called the Pascaline, to ease his father's arduous job of adding large groups of numbers. Pascal's machine used a complicated arrangement of numbered wheels arranged side-by-side and connected by gears that could add numbers up to nine digits.
In 1694 Gottfried Leibniz (1646-1716) improved on Pascal's machine by using a "stepped drum" gear that was a cylinder with nine bar-shaped teeth of incremental lengths parallel to the cylinder's axis. His design remained in use for more than two centuries; however, due to the accuracy needed in its construction, it did not become commercially successful until the mid-1800s. The machine generally performed addition and subtraction directly, but multiplication and division operations required manual assistance from the user. These machines usually contained a set of levers or keys to input a number, an indicator where the results appeared, and a revolution counter that could count the number of items added (or the number of times a number was multiplied or divided). In France Xavier Thomas de Colmar (1785-1870) invented a machine that could perform the four basic arithmetic functions (addition, subtraction, multiplication, and division). Colmar's mechanical calculator provided a more practical approach to computing because it could directly add, subtract, multiply, and divide. In the late 19th century, inventors began to produce calculating machines that were much smaller and less strenuous to use.
In the early 20th century, desktop adding machines and other calculating devices were developed. Some were key-driven, others required a rotating drum to enter sums punched into a keyboard, and later the drum was driven by an electric motor. By the 1940s motor-driven mechanical calculating machines became common sights on engineer's desks. While the hand-driven machines made addition fast and easy, these motor-driven models allowed multiplication and division to be fast and easy, too. However, the hand-driven machines continued to sell well because they were quieter, lighter, smaller, and less expensive.
Shortly after the Second World War Curt Herzstark (1902-1988) created and designed a small handheld, motor-driven device based on the "stepped drum" mechanism, but with a brilliant miniaturization adaptation that was remarkably simple. His device performed the four basic arithmetic functions, and later included operations for cubes and square roots. Besides being much smaller, Herzstark's computing machine was much faster and quieter than the older and larger hand-driven devices, and far less noisy and only slightly slower than the earlier motor-driven models.
Thus, by the late 1960s, hundreds of different types of calculating and adding machines had been invented that utilized many different technologies. These devices, even when refined for the desktop, were still large, heavy, and expensive when compared to modern calculators. But in 1967 three electrical engineers from Texas Instruments invented a portable, electronic, handheld calculator. Jack St. Claire Kilby (1923- ), widely recognized as the 1958 co-inventor of the integrated circuit (IC), along with Jerry Merryman and James Van Tassel, built an IC-based, battery-powered miniature calculator that could add, subtract, multiply, and divide. This basic calculator could accept 6-digit numbers and display results as large as 12 digits. These first "electronic" calculators were fairly large, typically performed only the four basic arithmetic functions and cost several thousand dollars when introduced, dropping to around US$1,000 by the late 1960s. Even though they cost more than contemporary mechanical calculators, the electronic calculators were popular because they were faster, quieter, easier to operate, and needed little or no maintenance. The continued development of miniature solid-state electronic devices lead to new electronic calculators that could: perform additional mathematical functions (such as trigonometric functions) in addition to the basic arithmetic operations; store data and instructions in memory files; provide programming similar to small computers; and could operate faster than their mechanical predecessors.
By the 1980s calculators were taking on many of the characteristics of today's modern calculators. As noted above, they could be programmed for certain functions and could store values in memory. But calculators still differed from computers in several ways: (1) calculators did not possess a fixed set of commands and did not (for the most part) recognize text, (2) they could not retrieve values stored in a data file, and (3) they could not find and use values generated by a program such as a spreadsheet.
Today, a calculator is generally rectangular in shape and contains a keyboard on which entered numbers and their results can be displayed. The simplest calculators posses a minimum of the following features: (1) on/off or power switch, (2) display, (3) memory function keys, (4) number (0-9) entry keys, (5) decimal point key, (6) percent key, (7) arithmetic (add, subtract, multiply, divide) function keys, (8) equal key, (9) square root key, and (10) clear/clear entry key. More advanced calculators now permit the user to store and access data from memory and give them the ability to use complicated geometric, algebraic, trigonometric, statistical, and calculus functions. Many calculators can also be programmed for specialized tasks. Calculators operate on electrical power supplied with batteries, solar cells, or standard electrical current. Modern calculators have digital displays, usually using some form of liquid crystal display.
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