Mac Hack is a

computer chess Computer chess includes both hardware (dedicated computers) and software capable of playing chess. Computer chess provides opportunities for players to practice even in the absence of human opponents, and also provides opportunities for analysi ...

program written by Richard D. Greenblatt. Also known as Mac Hac and The Greenblatt Chess Program, it was developed at the

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a Private university, private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of moder ...

. Mac Hack VI was the first

chess Chess is a board game for two players. It is an abstract strategy game that involves Perfect information, no hidden information and no elements of game of chance, chance. It is played on a square chessboard, board consisting of 64 squares arran ...

program to play in human tournament conditions, the first to be granted a chess rating, and the first to win against a person in tournament play. A pseudocode for the program is given in Figure 11.16 of. Its name comes from

Project MAC Computer Science and Artificial Intelligence Laboratory (CSAIL) is a research institute at the Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a Private university, private research university in ...

("Multi-Level Access Computer" or "Machine-Aided Cognition") a large sponsored research program located at MIT. The number VI refers to the

PDP-6 The PDP-6, short for Programmed Data Processor model 6, is a computer developed by Digital Equipment Corporation (DEC) during 1963 and first delivered in the summer of 1964. It was an expansion of DEC's existing 18-bit systems to use a 36-bit da ...

machine for which it was written.

Development

Greenblatt was inspired to write Mac Hack upon reading MIT Artificial Intelligence Memo 41,* or a similar document describing

Kotok-McCarthy Kotok-McCarthy, also known as A Chess Playing Program for the IBM 7090 Computer' was the first computer program to play chess convincingly. It is also remembered because it played in and lost the first chess match between two computer programs. ...

, which he saw while visiting

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

in 1965. A good chess player, he was inspired to make improvements at MIT in 1965 and 1966. In about 2004, he had an opportunity to tell

Alan Kotok Alan Kotok (November 9, 1941 – May 26, 2006) was an American computer scientist known for his work at Digital Equipment Corporation (Digital, or DEC) and at the World Wide Web Consortium (W3C). Steven Levy, in his book '' Hackers: Heroes of th ...

that searching the 7 best moves at each of the first two plies, and limiting the search depth to two would have done better than the default widths of "4 3 2 2 1 1 1 1", attempting eight plies in Kotok-McCarthy's REPLYS subroutine which generated each player's next plausible moves. Greenblatt added fifty

heuristic A heuristic or heuristic technique (''problem solving'', '' mental shortcut'', ''rule of thumb'') is any approach to problem solving that employs a pragmatic method that is not fully optimized, perfected, or rationalized, but is nevertheless ...

s that reflected his knowledge of chess. Mac Hack was written in MIDAS macro

assembly language In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence bet ...

on the

computer DEC donated to MIT (the first working PDP-6, serial number 2). Many versions may exist. During this period the program was compiled about two hundred times.

Tournament play

By the time it was published in 1969 Mac Hack had played in eighteen tournaments and hundreds of complete games. The PDP-6 became an honorary member of the Massachusetts State Chess Association and the

United States Chess Federation The United States Chess Federation (also known as US Chess or USCF) is the governing body for chess competition in the United States and represents the U.S. in FIDE, The World Chess Federation (FIDE). USCF administers the official national Chess ...

, a requirement for playing tournaments. In 1966 the program was rated 1243 when it lost in the

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

Amateur Championship. In 1967, the program played in four tournaments, winning three games, losing twelve, and

drawing Drawing is a Visual arts, visual art that uses an instrument to mark paper or another two-dimensional surface, or a digital representation of such. Traditionally, the instruments used to make a drawing include pencils, crayons, and ink pens, some ...

three. In 1967 Mac Hack VI defeated Ben Landy with a USCF

rating A rating is an evaluation or assessment of something, in terms of a metric (e.g. quality, quantity, a combination of both,...). Rating or rating system may also refer to: Business and economics * Credit rating, estimating the credit worthiness ...

of 1510 in game 3, tournament 2 of the Massachusetts State Championship. Greenblatt published the program with Donald E. Eastlake III and Stephen D. Crocker in MIT Artificial Intelligence Memo 174 and recorded some games there.

Influence

Mac Hack played by

teletype A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...

, was ported to the

PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...

and was the first computer chess program to be widely distributed. Mac Hack was the first chess computer to use a

transposition table {{no footnotes, date=November 2017 A transposition table is a cache of previously seen positions, and associated evaluations, in a game tree generated by a computer game playing program. If a position recurs via a different sequence of moves, the ...

, which is a vital optimization in game tree search. Greenblatt and Tom Knight went on to advance

artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...

and build the Lisp machine in 1973.

References

Bibliography

* Photo: ''Richard Greenblatt and Thomas Knight with the CADR LISP Machine at MIT'', * * {{Portal, Chess Chess software History of chess