early history of computer

The earliest known tool for use in computation was the abacus, developed in period 2700–2300 BC in Sumer. The Sumerians' abacus consisted of a table of successive columns which delimited the successive orders of magnitude of their sexagesimal number system.^[2] Its original style of usage was by lines drawn in sand with pebbles. Abaci of a more modern design are still used as calculation tools today.
The Antikythera mechanism is believed to be the earliest known mechanical analog computer.^[3] It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to c. 100 BC. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical astronomical clocks appeared in Europe.^[4]
Mechanical analog computing devices appeared a thousand years later in the medieval Islamic world. Examples of devices from this period include the equatorium by Arzachel,^[5] the mechanical geared astrolabe by Abū Rayhān al-Bīrūnī,^[6] and the torquetum by Jabir ibn Aflah.^[7] Muslim engineers built a number of automata, including some musical automata that could be 'programmed' to play different musical patterns. These devices were developed by the Banū Mūsā brothers^[8] and Al-Jazari^[9] Muslim mathematicians also made important advances in cryptography, such as the development of cryptanalysis and frequency analysis by Alkindus.^[10]
When John Napier discovered logarithms for computational purposes in the early 17th century, there followed a period of considerable progress by inventors and scientists in making calculating tools. In 1623 Wilhelm Schickard designed a calculating machine, but abandoned the project, when the prototype he had started building was destroyed by a fire in 1624. Around 1640, Blaise Pascal, a leading French mathematician, constructed the first mechanical adding device^[11] based on a design described by Greek mathematician Hero of Alexandria.^[12] Then in 1672 Gottfried Wilhelm Leibniz invented the Stepped Reckoner which he completed in 1694.^[13]
In 1837 Charles Babbage first described his Analytical Engine which is accepted as the first design for a modern computer. The analytical engine had expandable memory, an arithmetic unit, and logic processing capabilities able to interpret a programming language with loops and conditional branching. Although never built, the design has been studied extensively and is understood to be Turing complete. The analytical engine would have had a memory capacity of less than 1 kilobyte of memory and a clock speed of less than 10 Hertz.
Considerable advancement in mathematics and electronics theory was required before the first modern computers could be designed.