First. Among software designers, comes from C's and LISP's 0-based
indexing of arrays. Hardware people also tend to start counting at 0
instead of 1; this is natural since, e.g., the 256 states of 8 bits
correspond to the binary numbers 0, 1, ..., 255 and the digital
devices known as counters count in
this way.
Hackers and computer scientists often like to call the first chapter
of a publication ‘Chapter 0’, especially if it is of an
introductory nature (one of the classic instances was in the First Edition
of K&R). In recent
years this trait has also been observed among many pure mathematicians (who
have an independent tradition of numbering from 0). Zero-based numbering
tends to reduce fencepost errors, though it cannot
eliminate them entirely.
