The computer can recognize only two digits, the digits
zero and one.  For this reason its computational capability
is said to be based on the binary system of notation.  Most
systems, of course, use ten digits, zero through nine.  The
binary system can be compared to the on and off settings of
the common light bulb.  In truth, the light bulb, or vacuum
tube, formed the basis for the earliest computers; the bulb
had a value of one when it was on, and a zero value when it
was off.  These bulbs were bulky and gave off large amounts
of heat that had to be controlled by cooling the equipment.
     The early mainframe computers weighed tons in addition
to their being bulky, slow, and unreliable.  These problems
were largely solved with the development of the transistor,
a small device that replaced the vacuum tube.  Eagerly, new
computers were designed and marketed that were based on the
transistor.  These new and different computers were labeled
second generation computers.  However, the third generation
computer soon resulted from the brilliant research activity
that produced the chip, or miniature circuit.  The new chip
forms the basis of the computer that we now call the micro.