Chess Champion Mark V

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Chess Champion Mark V [1]

Chess Champion Mark V,
a dedicated chess computer manufactured by Scisys-W Ltd. Hong Kong from 1981. Primary author of a Z80 based development version was David Broughton, while the translation to the 6502 production version was done by Mark Taylor [2]. Both programmers were recruited into Levy's and O’Connell's company Philidor Software which was closely related to Winkler's Scisys-W Ltd. who manufactured and traded most of their computers until in summer 1981 Levy and O’Connell decided to loosen their relationship with SciSys and founded their new software company Intelligent Software [3] [4].


The Mark V had an LCD-board, a striking, futuristic design and many new features. For instance, it could play simultaneously on up to 12 internal boards.

SX Algorithm

The Chess Champion Mark V was mentioned to use the first version of the SEX Algorithm then called SX Algorithm , which used fractional plies for extensions and reductions [5] [6] :

Our first attempts to formalize this idea were in 1981 when one of us (David Broughton) replaced the usual integer depth (which simply controlled the maximum ply depth) with an integer SX. The SX parameter started out at the root node with some positive value, in a similar way to maximum depth, but instead of being decremented by one at each ply it would be decremented by a number determined by the type (or category) of move just made in the tree. When SX was decremented below zero this signaled the end of the search, except for the usual terminal node evaluations. 

While they started the first iteration of an ID framework with a SX-value of 10, which was incremented by 7 or 8 in further iterations, the depth decrement SXDEC was determined by static move properties, varying from 3 for the first check, to 7 for further tactical moves such as captures and attacking moves, up to 21, 24 or even 34 for non-tactical and apparently loosing moves. Those latter high decrements and reductions gave the Mark V the characteristic of a Shannon Type B program, which caused some tactical oversights with quiet moves involved, but made the program a strong mate solver for that time.

Initial Success

In September 1981, the Chess Champion Mark V won the commercial group of the 2nd World Microcomputer Chess Championship in Travemünde, West Germany. The initial success could not be sustained with a strong upgrade. The Chess Champion Mark VI [7] [8] module that followed a year or two later was only marginally stronger than the Mark V. A piece recognition sensory board was planned and patented but after much delay SciSys released a flawed auto sensory board instead. The Mark VI and sensory board were a commercial flop [9] .

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