Although I&#x27;m also not very familiar with the history of such schemes, I do recognize the (not quite) 12-bit one, which I believe was the first scheme proposed, by Claude Shannon in his 1950 article &quot;Programming a Computer for Playing Chess&quot; [1]. Perhaps because it&#x27;s naturally the first scheme anyone would come up with, but nonetheless, here&#x27;s what he had to say about it:<p>&gt; A move (apart from castling and pawn promotion) can be specified by giving the original and final squares occupied by the moved piece. each of these squares is a choice from 64, thus 6 binary digits each is sufficient, a total of 12 for the move. Thus the initial move P-K4 would be represented
by 1, 4; 3, 4. To represent pawn promotion on a set of three binary digits can be added specifying the pieces that the pawn becomes. Castling is described by the king move (this being the only way the king can move two squares). Thus, a move is represented by (a, b, c) where a and b are squares and c specifies a piece in case of promotion.<p>I&#x27;m actually slightly surprised Shannon didn&#x27;t propose a more compact scheme using the lower entropy of legal chess moves, but I guess his purpose in this article was more to do a ballpark estimate of the feasibility of computer chess playing in general.<p>[1] <a href="http:&#x2F;&#x2F;www.pi.infn.it&#x2F;~carosi&#x2F;chess&#x2F;shannon.txt" rel="nofollow">http:&#x2F;&#x2F;www.pi.infn.it&#x2F;~carosi&#x2F;chess&#x2F;shannon.txt</a>