Question

describe abacus as far as evolution of computer is concered

Answer 1

before the invention of computers abacus was only a device which was used as a calculator

Answer 2

An abacus is a manual aid to calculating that consists of beads or disks that can be moved up and down on a series of sticks or strings within a usually wooden frame. The abacusitself doesn't calculate; it's simply a device for helping a human being to calculate by remembering what has been counted.