If all the computers are digital then why we say that most of the computers are digital?

Answer 1

All computers are not digital.

Prior to the 1940s all computers that had ever been built were analog (only Charles Babbage's never built Analytical Engine designed in the 1830s was a digital computer in this period).

Even after the 1940s many computers were still analog and other computers were hybrid (part digital, part analog to best use the advantages of each to solve the problems as quickly as possible, at the lowest cost possible, while getting the needed accuracy). The image above shows a hybrid computer from the 1960s, the plugboards on the middle two racks are the means of programming the analog part of this computer for different problems.

In the 1980s I worked on an avionics box that the company I was employed by had designed for the Navy F/A-18A that contained 8 custom computers (6 digital and 2 hybrid) packed in a box 6 inches square by 2 feet long!

The usage of analog (and thus hybrid) computers has declined dramatically since the introduction of the microprocessor (which dramatically reduced both the size and cost of computers) and especially since the introduction of a special purpose type of microprocessor called a digital signal processor(specifically designed to solve the types of problems analog computers had been traditionally used for, except entirely by digital means). However there do still remain a few problems for which an analog computer is the only reasonable solution: problems that require near instantaneous results but can tolerate imprecise results (analog computers have many error sources due to a combination of component tolerances, drift, noise, etc. that digital computers do not). Digital computers are also much easier to program or reprogram when programming errors are found than analog computers (many analog computers would actually have to be completely dismantled and reassembled or just thrown away and completely replaced to "reprogram" them).