AMSTRAD CPC464 User Manual page 222

Through the medium of the program, the computer breaks down every task into a simple series of
Yes/No operations.
The process of multiplication is performed using multiple additions - the BASIC instruction to
multiply 35 by 10 (35*10) gets to the answer by adding 35 to itself ten times.
Part of the Central Processor Unit (CPU) is loaded with the numeric data for 10, and another part of
the CPU is loaded with 35. Each time 35 is added to itself, the part of memory containing 10 is
decreased by one until it reaches zero, when the process stops, and the accumulated result of 350 is
sent to another part of the CPU for Output as the answer.
If this process sounds cumbersome, then you' re quite right, as you have uncovered the first and most
important truth about computing. A computer is primarily a tool for performing the simplest of
repetitive tasks very quickly and with absolute precision, Thus BASIC interprets the instructions
given in the form of the program, and translates them into the language that can be handled by the
CPU. Only two states are understood by the logic of a computer - ' yes' or ' no' , represented in binary
notation as ' 1' and ' 0' . The representation in Boolean logic is simply ' true' and ' false' - there' s no such
thing as a ' maybe' or ' perhaps' .
The process of switching between these two distinct states is the essence of the term digital, and ' is
sometimes referred to as toggling. In the world of nature, most processes move gradually from one
completely ' stable' state to another in a smooth progression. In other words, the transition is made
by following the path of a line between the two states - in an ideal digital environment the switch
from one state to the next is made in no time at all - but the physics of semiconductor science dictate
that there will be some minor delay, referred to as propagation delays - and it is the accumulation of
many of these propagation delays that provides the reason why a computer has to spend some time
processing the information before the answer comes out.
In any case, the computer would have to wait a finite time for one task to have finished before it can
start work on the result of that first task - so there would need to be some artificial delay imposed
anyway. The digital process is black or white where the stages in the transition via shades of grey
have no significance whatsoever. The smooth progression is via various shades of grey.