Mark-I was the first electro mechanical computer developed by Howard Aiken. It was named as ASCC and was 8 ft high, 51 ft long and 2ft wide. It used more than 7 lakh 50 thousand parts and weighed more than 32 tons.

History of computer is based on mainly calculation devices. Therefore it is classified into the following three eras:

• Mechanical era.
• Electro-mechanical era.
• Electronic era.

Abacusis the first counting device, developed by Chinese and Egyptians, 2500 years ago. It performs mathematical concepts and arithmetical operations. It is a rectangular box, divided into two parts by mid bar , upper part is called heaven, consists of two beads and each bead equal to value 5 and lower part is is called earth, consists of five bead and each bead equal to value 1.

Napier's bone is multiplication tool invented in 1614 by mathematical John Napier of Scotland. The bones are a set of vertical rectangular rods, each one divided in 10 squares. John Napier is also the inventor of logarithms, a concept used to change multiplication into addition. Napier's bones was very successful and was widely used in Europe until mid 1960's. It is mainly used for multiplication table.