Colossus Chess 4


Sinclair ZX Spectrum

You can visist Colossus Chess official website at

This document was originally created by OCR scanning the "Colossus Spectrum/C64 Instructions", included in "The Classic Collection" compilation. Any specific reference to the C64 version has been removed. Chapters "Introduction" and "Program information" were added from Robin Stuart's "Colossus 4 Chess" document found on World of Spectrum archive, as these were missing on Classic Collection's original paper sheet. A few specific +3 Spectrum instructions were added. Published by Cristian Secară on January 2000. The specific +3 Spectrum commands as described here are only valid for the program version available on that site (look under ZX Zone section > +3 Software > Games).

Table of contents


General - This program is one of the best computer chess program available on any home computer. It is written using the very latest techniques by a computer chess programmer of ten years experience. It has been tested against a wide range of other chess programs and proven stronger than any of the opposition. It has the widest range of true features and sub-features available, including some never before implemented on any home computer chess program. The program also has a perfect understanding of all the rules of chess, including underpromotions, the fifty move rule and all draws by repetition. It can also handle all the standard mates including King and two Bishops versus King and the very difficult King, Bishop and Knight versus King.

Quick guide - This program has so many features, that at first you may be overwhelmed by the sheer size of the manual. However you do not have to read if from cover to cover but merely sample the relevant sections as your knowledge of the program increases.
The only section you should need to read to get started (apart from this introduction of course) are "Your Move" and "Cursor Movement". Then the most commonly used commands are "Go", "New Game" and "Type". After that, the other sections can be read at your leisure, as you discover the truly amazing features that the program has to offer.

Screen display

General - The display uses two screens to provide information as to the state of the game.
The main screen shows a graphical representation of the chess board showing the current game position and also various messages and questions as necessary. The letters and numbers around the board are those used in the algebraic notation for each square.
The second screen shows the past move record, including the player names and chess clocks and also information on the program thought processes, including lookahead positions examined, current-line and best-line with evaluation. The display can be toggled between the two screen by pressing the [SPACE] bar.

The move record - The secondary screen shows the last 6 moves made by each side in two columns, including move numbers. Above the moves are displayed the colours, player names and elapsed-time chess clocks for each side.

    The player names - Above each column is displayed the names of the white and black players. The programs name is displayed as "Colossus" while its opponents name is displayed as "Opponent".

    The clocks - Below the player names are displayed the elapsed time clocks for white and black. The clocks are in the format "hh:mm:ss" (hh=hours, mm=minutes, ss=seconds). The clocks show the total time used by each side in the game so far.

    The moves - The moves are displayed in algebraic notation with the from-square followed by the to-square. The separator between the from- and to-squares indicates whether the move is a capture or not ("x" signifies a capture, "-" signifies a non-capture). Castling moves are indicated with the from- and to-squares of the moving king. En-passant captures are indicated by the letters "EP" printed over the move. Promotions are indicated after the move by a "/", followed by a letter to indicate the promoted piece ("N"=knight, "B"=bishop, "R"=rook, "Q"=queen). Checks are indicated by a "+" being printed after the move.

Technical information - The bottom of the secondary screen is used to display detailed information of the programs thought processes. This information can provide a great insight into how a good chess program works, but only takes a fraction of one percent of the program thinking time to display it.

    Lookahead - When the program thinks about its move, it displays the lookahead depth of its search. The depth is printed in "ply" or "half-moves". The program will search most move sequences to at least this depth, with some being searched much deeper.

    Positions examined - The number of positions examined in the tree of move sequences is displayed. This number is updated after each iteration or when a new best-move is found. The program examines on average about 170 positions per second in the middlegame.

    Best line - The program displays the best line it has found so far in its search. This can provide you with the usual "hint" move and also an analysis of the game in the next few moves beyond the "hint"! (Usually the line will contain a "null" move. This simply means a passive, non-capturing move has been assumed). Also displayed is the evaluation of the best-line, as two numbers. The first is the material evaluation (in terms of number of pawns up or down), the second the positional evaluation. A positive number means the program is better, a negative number means the opponent is better. If the best-line is found to lead to a checkmate then the material score will be set to plus or minus 62, with the positional score a measure of how many moves to checkmate.

    Current line - The move sequence the program is currently considering is displayed. This can be seen to change as the search progress. The length of the line shown can be adjusted as required, using the "Quantify parameters" command.

    Assumed move - The program thinks on its opponents time. It assumes the opponent will make a particular move and then continues thinking about its next move. Sometimes the program will not have a move to assume and then will not think ahead. The move assumed is displayed so that you can follow the programs thought process and to provide a "hint" move. However, the quality of this move is for you to decide. If you play a different move from the one assumed, the time is wasted, but the program will correctly predict about one third of your moves on average.

Playing the Game

New Game - When a new game is started, the pieces are set-up in their initial positions, the clocks are reset to "00:00:00", the move display list cleared and you are give the option of moving first.
Type [SHIFT] "G" to make the program take white pieces and move first
(for further details see the "Go" command described later)

Your move - Whenever it is your turn to move, the program asks "Your move?" at the bottom of the main screen. You enter moves by the following cursor positioning method:

  1. Move the cursor to the square of the piece you wish to move and press the [ENTER] key or the Joystick [FIRE]. This causes the from-square to be displayed. If you accidentally enter the wrong from-square, it can be cancelled by pressing the [DELETE] key.
    (the cursor is shown as an inverse line drawn through the current square)
  2. Move the cursor to the square you wish to move to and again press [ENTER] key or the Joystick [FIRE]. This causes the to-square to be displayed. If the move is illegal, the message "Illegal" is displayed and the move entry cleared. You must then return to step 1 above and try again.
  3. If the move is a pawn promotion the program asks "Promote to?" You must specify the piece you want to promote to by typing one of the following: "N"-knight, "B"-bishop, "R"-rook or "Q"-queen. If you press any other key, the program assumes you promote to a queen.

Note: If you wish to enter a castling move, you should move the king two squares either way. If you wish to enter an en-passant capture, you should move the pawn as in a normal capture. The legal move is now indicated on the board, by flashing the cursor on the from-square, then moving the piece and flashing the cursor on the to-square.
(for further details see the "Cursor movement" command described later)

Colossus move - When the program computes its move it displays the message "Let me think..." below the board. The technical information on the secondary screen is updated as the search progresses. When the program has finished its search, it prints the selected move in the move-record and to the right of the board and also indicates it on the board (in the same way as your moves are indicated). Pressing the [DELETE] key whilst the program is thinking about its move will cause it to abort its search, display the message "Escape" and make the best move it has found so far. If the program has found that its move leads to checkmate, it announces the move with the message "Mate in N" where N is the number of moves till the mate.

Game over - When a game is completed, the clocks are stopped and the program displays a message to the right of the board, to indicate the final state of the game. The messages are:

    "Drawn" - the game has been drawn by 3 fold repetition of position, the 50-move rule or by neither side having enough material to mate the opponent; this occurs in the cases of King, King and Bishop, or King and Knight verses a lone King
    "Checkmate" - the side which moved last delivered checkmate
    "Stalemate" - the side to move is in stalemate
    "Time up" - the side to move lost "on time"; this occurs only if you are playing an "All the moves" game

The program then asks "What now?" and waits for you to enter one of the program commands.
Type [SHIFT] "N" to start a "New game".

Keyboard entries

Cursor movement - The cursor is indicated by an inverse line, drawn through the middle of the current square. It can be moved in three ways:

  1. Cursor keys. Four cursor controls, provide single square movement in any direction. The [LEFT ARROW] and [RIGHT ARROW] keys give left/right movement while the [UP ARROW] and [DOWN ARROW] keys give up/down movement. If the cursor is moved off one edge of the board, it reappears at the opposite edge.
  2. Algebraic keys. The cursor can be moved immediately to any rank, by typing one of the number keys "1" to "8". It can be moved to any file by typing one of the letters "a" to "h". This allows algebraic notation to be used when entering moves e.g. typing e2 [ENTER] e4 [ENTER] will enter the common opening move Pe2-e4. Note that if the rank or file of the from and to-squares is the same, the key sequence can be shortened, i.e. in the above example e2 [ENTER] 4 [ENTER] would also work.
  3. Joystick. Use of joystick is available to certain formats. Once loaded a message is printed to show current joystick status. The initial position of the cursor depends on the current side to move.
    If white is to move, the cursor starts on a1.
    If back is to move, the cursor starts on h8.

Numeric data - IMPORTANT - Please Read - Many of the programs commands require numbers to be entered to set-up new values of parameters etc. The program employs a simple to use, error-proof method for entering numbers. First the current value of the parameter is displayed at the query position. To increment the displayed value, use the [UP ARROW] key. If the new value is above the upper limit for that parameter then it is reset to its lower limit. To decrement a displayed value, use the [DOWN ARROW] key. If the new value is below the lower limit for that parameter then it is reset to its upper limit. To enter a new value into the program, press [ENTER].
(If you do not wish to change the current value, then press [ENTER] instead of using the "increment" or "decrement" keys).

Commands - The following commands can be entered when it is your turn to move, or when the game is over. To enter a command, press the [SHIFT] key, then type the first letter of the command's name (shown in capitals in the descriptions below). The commands are ordered alphabetically and are designed to be easy and logical to use and to greatly increase your enjoyment of the game of chess.

Note 1: If the selected command requires numeric input, and you are viewing the secondary text screen, then the program will automatically switch back to the primary graphics screen.
Note 2: If the command is entered, the any "thing on the opponents time" will be aborted.

Alter position: type [SHIFT] "A" Any legal chess position can be set-up with this command. When selected, the program displays the message "Alter position: SSSSS: Command?" (Where SSSSS is the side to move). When in "Alter position" mode, a further subset of commands allow you to adjust the board thus:

    Get initial data: type "G" If after changing part of the position you decide you have made a mistake, the initial position can be retrieved with this command.

    Move number: type "M" The program asks "Move number?" thus allowing you to enter the new move number required

    Side-to-move: type "S" This toggles the side to move between white and black. When pieces are added to the board, their colour is determined by the current side to move.

    Clear, Pawn, Knight, Bishop, Rook, Queen, King: type "C", "P", "N", "B", "R", "Q" or "K" To change a particular square, place the cursor over it and enter one of the above, to determine the new status of that square. Note that algebraic control of the cursor is not available in "Alter position". When a square is changed, the cursor will move over one square to the right to make the setting up of complete rows of pieces very easy.

    Wipe: type "W" This removes all pieces from the board, thus allowing positions with very few pieces to be set-up more quickly.

    New game: type [SHIFT] "N" The "New game" command is still available when in "Alter Position" mode.

    Exit: type "E" This allows you to exit from "Alter position" when the required position has been achieved. If the position is illegal for any reason, the message "Illegal" is displayed and "Alter position" will not be exited. You must then correct the error before exiting.
    Illegal positions occur with any of the following:

      either side has no king
      either side has more than one king
      the side not to move is in check
      either side has a pawn on the first or eighth rank
      either side has more than eight pawns or promoted pieces

    When you exit "Alter position", if you made any changes, the current game-record is cleared of all previous moves, so that you cannot "Back-step" through these (now possibly illegal) moves. Note that changing the side-to-move or the move-number is also considered as a change.

Back-step: type [SHIFT] "B" & For-step: type [SHIFT] "F" All the moves in the game are stored in the programs memory. This allows you to step backwards or forwards throughout the game record, to get to any required position. This can be used for several reasons:

    e.g. After you accidentally lose a piece, you can recover your error by using Back-step.
    e.g. If you wish to try a different line earlier in the game, you can Back-step to the required position and then carry on playing the different line.

Colours: type [SHIFT] "C" The piece, square, border, ink and paper colours can be set to any of the eight available colours. The piece and square colours are only used for the 2D board display. The only limitation is that the ink and paper colours cannot be the same because this would cause the display to "disappear". If you try to enter conflicting colours, the message "Illegal" will be displayed and you must re-enter another colour. Note also for the 3D display - you should use a lighter colour for the ink than the paper or the piece "colours" will appear inverted, i.e. the "white" pieces will appear darker than the "black" pieces.
The default colours are: light-piece = 7(white), dark-pieces = 0(black), light-square = 4(green), dark-square = 2(red), border = 2(red), ink = 7(white), paper = 1(blue).

tape: type [SHIFT] "D" This allows you to save and/or load move-records and position to/from the tape. The program asks "Load or Save?" Type "L" to load a previously saved record, or "S" if you wish to save the current record. Any other keypress will abort the "tape" command. The program then asks for a file number (from 0 to 255), which is used as part of the file name on the tape.
If any errors occur during loading, the current move record will be lost. Note that the program parameters, such as playing speed, elapsed time, are not saved and so may need to be reset after loading. The [BREAK] key can be used to abort saving and loading early.

Disk & printer for +3 Spectrum version: type [SHIFT] "D" This allows you to save and/or load move-records and position to/from the disk. Please refer to the "tape" command described above and consider "disk" instead of "tape" where necessary.
Additional information:

  • Make sure you have a floppy disk inesrted and the write-protect tab is set to off. Files are saved as "COLOSSnn.USR", where nn is the hex value of the number entered during the file handling command described above.
    Although you can have a maximum of 256 user files saved on a single floppy disk and each file is 867 bytes long, original Amstrad CF-2 180K SS, DD floppy disks capacity limits the user saved files to a maximum of 178 (assuming a fresh formatted floppy disk is used, using the +3 Basic "format" command).
    This limit does not apply when using 720K DS, DD floppy disks.
    IMPORTANT - please read
    • The program does not warn in case of saving over an existing file name. The program will replace any existing file that happens to have the same name, without any further notification.
    • If any errors occur during saving and/or loading, the message "Error" will be displayed. No further explanation is given about the nature of that error.
  • A screen dump option has been added in addition to the file handling commands. On +3 version of Colossus Chess, the program asks "Load, Save or Dump?" Type "D" to copy the screen image to the printer. The actual printer routines are based on the +3 Basic "copy exp" command. To change from parallel port to serial port, or to modify the baud rate, use the standard +3 Basic commands BEFORE loading Colossus Chess. The [BREAK] key can be used to abort printing early. If the printing was not successfully finished, the message "Error" will be displayed.

Elapsed-time clocks: type [SHIFT] "E" The elapsed time clock for both sides can be set from 00:00:00 to 255:59:59. First the program asks for the new value for the white clock and then the new value for the black clock.
This can be used to set-up reasonable values for the elapsed time clock, if you change the playing speed in mid-game. The program makes extensive use of the elapsed time clocks to determine how quickly it should play e.g. if you increase the elapsed time on the programs clock it will then play quicker to keep within the average time it is currently set to.

Go: type [SHIFT] "G" This forces the program to move for the current side to move. This can be used repeatedly to make the program play several moves against itself or to force the program to resume play, for the side to move, after the "Supervisor" command has been entered. It also allows you to switch sides with the program in mid-game.
After a new game has been initiated, this will make the program play for white. In this case the program automatically clears the clocks and sets the orientation for you to play the black pieces up the board.
This command is ignored if the game is over.

Invisible: type [SHIFT] "I" This allows you (if you feel confident enough) to play the equivalent of a game of "blindfold" chess, as sometimes done by strong chess players. The program asks "Invisibility?", when you must enter a number from 0 to 3. The number entered determines which pieces on the board are made invisible:

    0 - is the default value where both sides are displayed
    1 - will make the white pieces invisible
    2 - will make the black pieces invisible
    3 - will make all the pieces invisible

The moves are still indicated on the board and displayed in the move record.
When "Invisible" is selected, the word "Invisible" appears at the top right of the board, to avoid confusion.

Joystick: type [SHIFT] "J" The joystick can be switched on/off with this command. A message is printed to show the current joystick status.
The program assumes the joystick has a Kempston interface type.

Legal moves: type [SHIFT] "L" All the legal moves by any piece of the side to move can be shown. First, position the cursor on the subject piece and type [SHIFT] "L". The legal moves will be shown in sequence by flashing the cursor on the target squares. The cursor is then returned to the subject square. If no legal moves exist the cursor will not move. This can be used as a tutorial aid for learners.

New game: type [SHIFT] "N" A new game can be started with this command. If you have not used "Alter position" since the last "New game", then the game record is left intact until the first move of the new game is entered. This allows you to replay through the whole of the last game, by using the "For-step" or "Replay" commands.

Orientation: type [SHIFT] "O" The orientation of the board printout can be reversed, so that you can play the black pieces up the board. The algebraic notation around the board is also reversed. This is most useful when you wish to play black against the program.

Play self: type [SHIFT] "P" This makes the program play a game against itself, by moving for both sides. When a game is completed, the program pauses for a few seconds, to allow you to study the final position and then starts a new game automatically. This command is ignored if the program is in "Infinite" or "Problem" mode, or the game is over. Pressing the [DELETE] key whilst the computer is thinking about its move (but not while it is indicating its move on the board), or after the game is over, will stop the program playing against itself and allow you to resume play for the current side to move. When playing itself, both player names are displayed as "Colossus".

Quantify parameters (& 2D/3D graphics): type [SHIFT] "Q" This allows you to adjust some of the programs internal parameters to make it function in different ways.

    The program first asks "Book?" The parameter can be 0 or 1. If it is set to 0 the program will not search its "openings book" for moves (effectively making the openings easier for you). If it is set to 1 the program will use its book in the normal manner.

    The program then asks "Prediction?" The parameter value can be 0 or 1. If it is set to 0 the program will not predict your move or think ahead on your time (effectively making the whole game easier for you). If it is set to 1 the program will predict your move in the normal manner.

    The program then asks "Line depth?" The number of moves in the "current-line" display can be set from 1 to 12 ply. The default is 1, i.e. the moves at the first play of the tree are displayed.

    The program then asks "Dimensions?" The parameter value can be 2 or 3. If this is set to 2 the graphics board printout will be the two-dimensional (2D) representation as used in chess literature. If it is set to 3 (the default) the board is displayed as three-dimensional (3D) as though you were looking at a real board and pieces.

    The program then asks "Draw score?" The "material" part can be set from -9 to +9 and the "positional" part from -60 to +60. The lower the draw score is set the more the program will keep trying to win. The higher the draw score is set the more the program will be happy to allow a draw (effectively making it easier for you to achieve a draw by repetition of position).

Replay: type [SHIFT] "R" The whole game-record can be replayed from the start to the final position to demonstrate the game-so-far to a spectator. The program pauses between moves to allow you to follow the game. The pause time can be set from 0 to 20 seconds.
You can interrupt the replay by pressing the [DELETE] key during one of the pauses. When an action replay is in progress, the message "Replaying" is displayed below the board.

Supervisor: type [SHIFT] "S" This stops the program making any moves and allows you to play moves for both sides. This allows you to set-up a required position by playing through a sequence of moves, or to play a friend using the programs board display. All moves entered are still checked for legality. When supervising, both player names are displayed as "Opponent".

Type of playing mode: type [SHIFT] "T" The program has six modes of play, to allow different speed and style games to be selected. The more time you give the program to think about it move, the better it will play. The program asks "Type?" to allow you to select one of the following:

    1 - Tournament mode
    Full tournament parameters can be set-up.
       First, the program asks for the move number of the first time control.
       Second, the program asks for the number of moves to secondary time controls.
       Third, the program asks for the time of the first time control.
       Fourth, the program asks for the time to the secondary time controls.
    The program is not strict about your time control and will not claim a win "on time" if you exceed any time control. The program will usually never exceed its own time control.

    2 - Average mode
    This is really an easy usage version of Tournament mode. Instead of entering all four parameters needed for Tournament mode, the program simply asks you "Move time?" The program will then control its search to use on average the time you enter (entering 0 seconds for the average move time selects the programs fastest level). This effectively provides thousands of "levels" of play.

    3 - All the moves mode
    In chess clubs, most games are played with chess clocks, with each player having say five minutes to complete a game or "lose on time". This mode allows you to set the complete game-time and the program will try to play all the moves of the game within the specified time. If either player exceeds the game time, the game will be terminated wit the message "Time up". By using the "Elapsed-time clocks" command, you can "handicap" the program or yourself, by putting some time on one of the clocks before starting the game. This can be very useful for players who are much worse or much better than the program.

    4 - Equality mode
    In this mode, the program will attempt to keep its elapsed time clock, closely matched to your elapsed time clock, effectively playing at a sililar speed as you are playing. If you make several quick moves, the program will also probably have to play quickly to keep up with the "pace" you are setting. If however, you think for a long time over some moves, the program will also be able to think longer over its moves. In practice, the programs clock will usually trail yours by a few minutes.

    5 - Infinite mode
    This mode can be used to solve chess puzzles of the form "find the best move in this position". It searches all combinations of all moves to ensure that it does not miss a sacrifice. It continues searching, further and further ahead, until you tell it to stop, or it finds a forced checkmate for either side, or it has searched 12 ply ahead (the programs maximum lookahead), or there is only one legal move in the position. This is very useful for postal chess games where you can just leave the program running overnight (or sometimes even longer) to find the best move. When the program starts searching for the move, the clocks are set to 00:00:00, so that the time taken on the move can be recorded. Also note that the openings book is not searched in this mode. Of course, the program may find the same move in much less time using its normal playing mode, because certain "obviously bad" moves are ignored.

    6 - Problem mode
    This mode is used to solve chess mating problems. When selected the program asks "Problem Type?" The number entered determines one of the three problems the program can solve:

      1 - Normal mates - of the form "White to move and mate black in N moves"
      2 - Self mates - of the form "White to move and force black to mate white in N moves"
      3 - Help mates - of the form "white to move and help black to mate white in N moves"

    The program then asks "Mate in?", whereupon you must enter the number of moves till the intended mate. The program can solve mates up to 7 moves ahead. When the program starts searching for the mate, the clocks are set to 00:00:00, so that the time to find the mate can be recorded.
    If the program finds a mating move, it prints the mating line below the move record, stops the clocks, and asks "Continue?" If you are satisfied with the discovered move, then pressing "N" will cause the program to make this move immediately. If however, you wish the program to continue searching for any alternative mate, press "Y" and the program will restart the clock and continue searching for another mate. This process is repeated until no more mating moves are found, in which case the program will then make the last mating move found on the board. If the program does not find any mate, the message "No mate" is displayed and the program automatically enters "Alter position" to allow you to select another position or correct the current one.

Use next best: type [SHIFT] "U" After the program has made a move, you can instruct it to choose a different move from this remaining. You can use this repeatedly until all the moves have been used up. When no more moves are available, it prints the message "*NO MORE MOVES*" and starts again choosing from the whole move list. If the program is still using its openings book, it will choose the next book alternative (selected at random). This can be used to examine the programs book choices to select the line you prefer. (No non-book moves are considered!) If the program is out of book, it will choose the move it considers to be its next best choice from the remaining moves.

Volume: type [SHIFT] "V" The programs "beeps" can be turned off/on with this command. When the sound is turned off, no further "beeps" will be heard.

Program Information


    Author: Mr. Martin P. Bryant
    Publisher: CDS Software Ltd., CDS House, Beckett Road, Doncaster, South Yorkshire, England
    Language: Z80 assembly
    Code size: 36K
    Data size: 5K
    Positions examined per second: 170 (average)
    Estimated Rating: 1850+ELO (156+BCF)

Openings book - The program has an openings "book" of about 3000 positions, which it uses to play the first few moves of the game quickly and accurately. Lines vary from 2 ply to 17 ply deep. When there is a choice of book moves at any position, the program will choose between them at random, with a slight bias towards the moves which the program itself considers best.