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The difference of valid 0x88 coordinates A and B is uniquely with respect to [[Distance|distance]] and [[Direction|direction]], which is not true for classical packed three bit rank and file coordinates (for instance -+7 may occur on [[Ranks|ranks]], [[Anti-Diagonals|anti-diagonals]]). That makes lookups for [[Distance|distance]], [[Manhattan-Distance|Manhattan-distance]], possible piece attacks and that like, much more resource friendly. While classical square coordinates in the 0..63 range require 4K (64*64) sized tables, the 0x88 difference takes 1/16 or 256 sized tables - or even 16 less.

When I was at the Hong Kong [[WCCC 1995|WCCC in 1995]], I had some conversations with [[David Kittinger]]. He told me about a [[Move Generation|move generation scheme]], whose name I promptly forgot. When I came back home, I explained this scheme online many times. Since I didn't know the name, I couldn't give it the proper name, and it kind of acquired a name. The name that seems to have stuck is "0x88", which is means [https://en.wikipedia.org/wiki/Hexadecimal hexadecimal] 88. The reason it's called 0x88 is that this constant is critical in the implementation of the scheme.

I was told this technique at I believe the [[WMCCC 1981|Travemunde world championship]] . It just involved using 0rrr0ccc encoding. The advantage was that (sq + offset) & 0x88 would tell you if off board. Many of and on the devices I programmed on took longer to read ram than test a register result. Also, immediate test for < 0 (byte value) could test for off board, so faster off board test than accessing a 'collar' utilization of off board values. The fellow who told me this attributed it to [[Mikhail Botvinnik|Michael Botvinnik]] (Former USSR World Champion) as something used in a version of [[KaissaMemory]] <ref>presumably in [[Pioneerhttp://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=462700&t=43447 Re: Hello all]], see also by [[Boris StilmanDavid Kittinger|Dave Kittinger]] ('''1994'''). ''A Linguistic Geometry of the Chess Model''. , [[Advances in Computer Chess 7CCC]], April 26, 2012</ref>. However, when I was riding an elevator w/Mr. Botvinnik and asked him about this to confirm the derivation, one of his handlers asked that I not ask Mr. Botvinnik any questions.

Another advantage of the 0rrr0ccc was that I put the 'ioboard' at 0rrr1ccc so basically used 1/2 a page of ram efficiently for both boards... I would then have the piece table at 1000wwww and on 1000bbbb for the utilization of [[Memory]] <ref>[http://www.talkchess.com/forum/viewtopicwhite and black pieces respectively just to pack things in.php?topic_view=threads&p=462700&t=43447 Re: Hello all] by [[David Kittinger|Dave Kittinger]], [[CCC]], April 26, 2012</ref>

Another advantage ... and the difference of the 0rrr0ccc was that I put the 'ioboard' at 0rrr1ccc so basically used 10x88 coordinates <ref>[http://2 a page of ram efficiently for both boardswww.talkchess. I would then have the piece table at 1000wwww and 1000bbbb for the white and black pieces respectively just to pack things incom/forum/viewtopic.php?topic_view=threads&p=462734&t=43447 Re: Hello all] by [[David Kittinger|Dave Kittinger]], [[CCC]], April 27, 2012</ref>

... and the difference of 0x88 coordinates <ref>[http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=462734&t=43447 Re: Hello all] by [[David Kittinger|Dave Kittinger]], [[CCC]], April 27, 2012</ref>  The whole 0x88 is pretty obvious. In fact, another big benefit is that you could take the difference of two sqs and use that to look into a table to see the legal piece types that could be attackers. Having bit 3 cleared prevented wrap around on this look up. Hence, for most my programs the basic capture routine iterated from [[MVV-LVA|largest to smallest captured piece]], using smallest to largest capturing piece, taking the difference of the sqs, looking up in att_table and seeing if nz, if nz, then if & with attacker type bit nz then just had to check if [[Sliding Pieces|slider]] and had [[Square Attacked By#By0x88Difference|path clear]]. Of course, w and b pawns had different [[Pieces#PieceTypeCoding|type]] bits. Made for a decently fast and ordered [[Quiescence Search|capture search]].