A microcomputer can be defined as a small sized, inexpensive, and limited capability computer. It has the same architectural block structure that is present in a computer. Present-day microcomputers are having smaller sizes. Nowadays, they are of the size of a notebook. But in coming days also their sizes will get more reduced as well. Due to their lower costs, individuals can possess them as their personal computers. Because of mass production they are becoming still cheaper. Initially in the earlier days they were not very much powerful. Their internal operations and instructions were very much limited and restricted. But at present days, microcomputers have not only multiply and divide instructions on unsigned and signed numbers, but are also capable of performing floating point arithmetic operations. In fact they are becoming more powerful than the mini computers and main computers of yesteryear.
As an example, the Commodore 64 was one of the most popular microcomputers of its era, and is the best-selling model of home computer of all time.
So a microcomputer is a small, relatively inexpensive computer with a microprocessor as its central processing unit (CPU). It includes a single printed circuit board containing a microprocessor, memory, and minimal input/output (I/O) circuitry mounted. With the advent of increasingly powerful microprocessors, microcomputers became popular in the 1970s and 1980s. The predecessors to these computers, mainframes and minicomputers, were comparatively much larger and more expensive (though indeed present-day mainframes such as the IBM System z machines use one or more custom microprocessors as their CPUs). Also we can mention that, many microcomputers, in the generic sense, (when equipped with a keyboard and screen for input and output) are also personal computers.