he first electronic computer was completed in 1946 by a team led by Professors Eckert and Maunchly at the University of Pennsylvania U.S.A. This computer, called Electronic Numerical Integrator and Calculator (ENIAC) used high speed vacuum tubes. It has a very small memory and was designed primarily to calculate the trajectories of missiles. The ENIAC took about 200 microseconds to add two digits and about 2800 microseconds to multiply.
In 1946 John Von Neumann proposed an idea to store machine instructions in the memory of the computer along with data. The first computer using this principle was designed and commissioned at Cambridge University, U.K., under the leadership of Professor Maurice Wilkes. This computer called EDSAC (Electronic Delay Storage Automatic Calculator) was completed in 1949 and used mercury delay lives for storage.
Commercial production of stored program electronic began in the early 50s. One of the early computers of this type UNIVACI built by Univac division of Remington Rand and delivered in 1951. This computer also used Vacuum tubes. As vacuum tubes used filaments as source of electrons, they had a limited life. Each tube consumed about half a watt power. Computer typically used about ten thousand tubes. Power dissipation was very high.
With the advent of UNIVAC, the prospect of commercial application was perceived. The concept of operating system had not yet emerged. During this period one had to be a good electronics engineer, and understand the logical structure of computer in great detail, and also know how to program an application in order to use a computer.