Human Computer

Before computers became commercially available, the term Computer , in use from the mid 17th century, literally meant one who computes: a person performing mathematical calculations. Teams of people were frequently used to undertake long and often tedious calculations; the work was divided so that this could be done in parallel.

Mechanical Calculating Device

A calculator is a device for performing mathematical calculations, distinguished from a Computer generally by a limited problem domain and an interface optimized for interactive calculation rather than programming. Calculators can be hardware or software, and mechanical or electronic, and are often built into devices such as PDAs or mobile phones.

A basic calculator

Modern electronic calculators are generally small (often pocket-sized) and usually inexpensive. In addition to general purpose calculators, there are those designed for specific markets; for example, there are scientific calculators which focus on advanced math like trigonometry and statistics. Modern calculators are more portable than most computers, though most PDAs (Personal digital assistants) are comparable in size to handheld calculators.