The General purpose mechanical computers were developed In 1930. These were mainly for the use of mechanical calculations. They were built for automatic addition, subtraction, multiplication & division. They were calculator like in nature hence not programmable.
Below are is a discussion of the computer evolution from mechanical to electronic:
(1) Mechanical Era: There were many attempts to create a machine that could help to perform various calculations. In 1823, Charles Babbage tried to build a mechanical as computing machine capable of performing automatic mathematical calculations. This was designed to compute tables of functions such as logs functions etc. In 1830's Babbage made a more powerful mechanical computer. This machine was designed to perform any mathematical calculation automatically. It could perform addition etc. It had a memory unit. Its capacity was 1000 numbers, each no. consisting of 50 digits. The machine was a programmable one. It had mechanism for enabling a program to change the sequence of its operations automatically. In the late 19th century punched cards were commercially used. Soon IBM was formed in 1924. Konand Zuse developed a mechanical computer, the Z1, in 1938 in Germany.
(2) The Electronic Era: The first electronic computer using valves were developed by John V. Atanas off in the late 1930's. It contained add- subtract unit. It was relatively a small computer and used about 300 valves. Its memory unit consisted of capacitors mounted on a rotating drum. It used a number of I/O devices including a card punch and a card reader. The first popular general electronic digital computer was the ENIAC (Electronic Numerical Interpreter and calculator). John von Neumann was The consultant of the ENIAC project. The ENIAC used a high speed memory to store both programs as well as data during program execution. Neumann and his colleagues designed and build the IAS Computers. It used RAM consisting of a cathode ray tube. The transistors were invented in 1948 at AT&T bell laboratories. Slowly they replaced Vacuum tubes. IC's were first introduced, i.e. designed and fabricated in 1958-59. The examples of computers using IC's are-: IBM – 370 & PDP-8. In 1970 LSI chips were introduced is form of memory units. Computers built in 1970's & onwards used micro process and other LSI, VLSI and ULSI components.