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 land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...

. Mac Hack VI was the first

chess Chess is a board game for two players, called White and Black, each controlling an army of chess pieces in their color, with the objective to checkmate the opponent's king. It is sometimes called international chess or Western chess to disti ...

program to play in human tournament conditions, the first to be granted a

chess rating A chess rating system is a system used in chess to estimate the strength of a player, based on their performance versus other players. They are used by organizations such as FIDE, the US Chess Federation (USCF or US Chess), International Correspon ...

, and the first to win against a person in tournament play. Its name comes from

Project MAC Computer Science and Artificial Intelligence Laboratory (CSAIL) is a research institute at the Massachusetts Institute of Technology (MIT) formed by the 2003 merger of the Laboratory for Computer Science (LCS) and the Artificial Intelligence Lab ...

("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, which he saw while visiting

Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...

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, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, ...

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

assembly language In computer programming, assembly language (or 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 be ...

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 In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

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. US Chess administers the official national rating s ...

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

Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...

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

drawing Drawing is a form of visual art in which an artist uses instruments to mark paper or other two-dimensional surface. Drawing instruments include graphite pencils, pen and ink, various kinds of paints, inked brushes, colored pencils, crayons, ...

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 quality, quantity, or some combination of both. Rating or ratings may also refer to: Business and economics * Credit rating, estimating the credit worthiness of an individual, c ...

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. Initia ...

, 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 intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech re ...

and build the

Lisp machine Lisp machines are general-purpose computers designed to efficiently run Lisp as their main software and programming language, usually via hardware support. They are an example of a high-level language computer architecture, and in a sense, the ...

in 1973.

References

Notes

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