backbone site = B = background


See bignum (sense 3), moby (sense 4), and pseudoprime.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Atari 2600 Game
Produced by: Atari and Sears
Model Number: CX2617 (Atari) or 99848 (Sears)
Rarity: 2 Common+
Year of Release: 1978
Programmer: Uncredited

Why carry around a bulky Backgammon set, when you can now fit Backgammon in your pocket? You can play anytime with Backgammon for the Atari 2600.

This is the Backgammon, properly implemented. This is nothing fancy, but it does get the job done. The Acey Deucey variant is also included. The manual to this game is a wonderful reference on the rules and history of this game. I can't node the whole thing because of silly laws, but I will include an excerpt from the beginning.

From the manual

Backgammon, in some version, has been played in various parts of the world for over 5,000 years. It is possibly the oldest war game still being played. It is suggested in early writings that the game was originally designed to train soldiers for combat, as backgammon has all the intricacies of any war game: strategy, position, and timing. It is both a game of skill and luck, which probably accounts for its longevity.

The most ancient possible ancestor to be found so far dates back to the ancient civilization of Sumer. The Egyptian Pharaohs played a similar game. Game boards were found during the excavations of King Tut's tomb that akin to backgammon. The ancient Greeks and Romans played different forms of the game were mentioned in many of their writings. A form of backgammon was played in the Middle East long the Crusades. In fact, it is believed that the Crusaders brought the game back to Britain with them, where it flourished in the eighth and ninth centuries.

The earliest written mention of the name "backgammon" was made in 1645, in a description of a game that is very much like backgammon as it is played today. The rules of today's game were set down by Edmond Hoyle in 1743.

The object of all the variations of the game, from its beginnings to now, is to move you game pieces around the board and bear them off before your opponent does.

Collectors Information

This game was sold under both the Atari and Sears brand names. There are two label variations of the Atari version (1 with text, 1 with a picture). The Sears version had a text label. This game is valued at around $2 USD. As always, games with boxes and manuals are worth more.

Backgammon, although it seems complex on first glance, has rules which are actually rather simple. The hardest part is remembering how to set up the board.

Actually, it's very difficult to explain the rules without diagrams. ASCII representation is rather a poor substitute.

Here we have two players, o and Q, sitting down to play. Q is sitting at the top of the board and o at the bottom.


    | /------------> Q's HOME
    | | =================
    | | |o...Q.| |Q....o|
    | | |o...Q.| |Q....o|
    | | |o...Q.| |Q.....| <-- Q's HOME
    | | |o.....| |Q.....|
    | | |o.....|B|Q.....|
    | | |------|A|------|
    | | |Q.....|R|o.....|
    | | |Q.....| |o.....|
    | | |Q...o.| |o.....| <-- o's HOME
    | | |Q...o.| |o....Q|
    | | |Q...o.| |o....Q|
    | | =================
    | \---------------Q                
    \----------> o's HOME

Q and o have two dice each, and somewhere near the board is the doubling cube.

There are four variations on the start.

  1. o and Q roll all four dice. The player with the larger total goes first by rerolling hir dice.
  2. o and Q each roll one die. The player with the larger number goes first by rerolling both hir dice.
  3. As 1), except that the winner uses hir winning roll.
  4. As 2), except that the winner uses the numbers on the dice on the table as hir roll.
is to bear off all your pieces from the board before your opponent, by first bringing them to your home board.

Patience, young one; all will be explained.

On each player's turn, s/he rolls both dice, and moves the corresponding number of spaces.

One of the more counter-intuitive parts of backgammon is that when the dice are rolled, both numbers are used rather than the total. That is, if Q rolls a 3 and a 5, he can:

  • move one piece 5 and another 3, or vice versa, or
  • move one piece 3 and then 5, or vice versa.
If doubles are rolled, the player gets to move four times the doubled number (i.e. if Q rolls 2 and 2, he gets 4 2s to use as he sees fit (moving one piece 2-2-2-2, moving one piece 2-2-2 and another 2, etc.))

Pieces move individually in the directions indicated above; o's pieces move counterclockwise around the board towards her home at the bottom, and Q's move clockwise towards his home at the top.

The pieces can move to any open point:

       <----- o moves this way
        (1)(2)   (3)(4)
        |Q..Q..| |Q....o|
        |...Q..| |Q.....|
        |......| |Q.....|

(1) is open.
(2) is not open.
(3) is really not open.
(4) is open.
So if o rolled 5 and 6, she would have to play the 6 first since the spot she would go on a 5 ((3)) is blocked. She would still end up landing on the same place (1), eleven spaces from where she started, but can only arrive there in that way.

Landing on (1) is also what o wants to do, since by landing on a space occupied by one (and only one) of Q's pieces (called a blot) to the bar.

Players must use all moves open to them. Thus, if o rolls a 5 and a 2, she must move the 2 first and then the 5; the 5 is blocked and she cannot move there, but she has to move according to both rolls. If she rolls a 2 and a 6, she can only use one of the rolls (moving eight spaces would land her on (2), which is blocked). Some players claim you must use the larger roll if you can't use both (and it's open); others let you have the choice. If both numbers are blocked (not illustrated above; use your imagination) then o has to pass her turn to Q.

Now that Q is on the bar, his priority changes from moving pieces towards his home to taking his piece off of the bar. Q rolls both dice normally, but rather than moving pieces around the board, he places them on o's home board like so:

        ..| |......|
        ..| |o.....|
        ..|B|o.....|  <-- o's HOME
If he rolls a 6 or a 4, he's stuck; those spaces are blocked (as above). If he rolls a 5, he can place the formerly barred piece on that space and use his other roll normally. If he rolls a 1 or 2, he's fine; he places his piece on either space and continues normally. If he rolls a 3, he's even more in luck, because his piece comes off the bar and replaces o's, which is sent to the bar. He can then use his last die roll. o now has to try to take her piece off. If Q rolled 6 and 4, then he's out of luck and must pass to o. If he can remove his piece from the board but can't move afterwards (in this example, by rolling a 3 and 4), he can remove the piece (to 4) and then his turn is over (unless he can move other pieces on the rest of the board, of course).


        .| |.QoQQQ|
        .| |...QQQ|
        .|B|...QQQ| <--Q's HOME
        -| |------|

Now Q finally has all of his pieces on his home board. He can now start to bear off, or remove his pieces from the board.

On each roll, he can either remove a piece from the corresponding space, or move pieces closer to the 1 space.

From the arrangement we have above, Q rolls his dice. Let's see what he can do with each roll.

1 -- he can either remove a piece from the 1 space, move a piece from 2 onto 1, 3 onto 2, or 5 onto 4 (hitting o's blot and sending her to the bar in the process).
2 -- a piece from 2 can be removed, a piece from 3 can be moved to 1, or a the piece on 5 can be moved to 3.
3 -- a piece from 3 can be removed, or the piece at 5 can go to 2.
4 -- since the piece at 4 is o's, Q can't do anything to it (save hitting it with a 1, but we talked about that earlier). His only move is to move the 5 piece to 1.
5 -- the piece at 5 must be removed.
6 -- the piece at 5 must be removed. If the number rolled is higher than the space of the last available piece, the player can remove the piece from that next lowest space. (Q couldn't remove a piece from 3 by rolling a 4 because there's still a piece at 5.) If it's o's turn, she can still send Q to the bar by rolling a 1. Q must then free his piece from the bar and work that piece all the way back to his home board (from o's!) Of course, Q still has both of his dice, and can roll a 5-4 removing pieces from 5 and 3, or whatever. Doubles (especially 6s) are particularly good in this situation, for reasons that may or may not be obvious.

As mentioned above, the object is to bear off all of your pieces before your opponent bears off all of hirs. If your opponent hasn't even started to bear off pieces (in the example above, o still has a piece on 4; if she couldn't get that piece around in time, she can't start to bear off), this is called a gammon, and the winner gets 2 points (one for the game, one for the gammon). If the loser has yet to bear off and has a piece on the bar besides (say, if o hits Q and then not only gets her piece over to to her home board but also bears off all of her pieces before Q gets off the bar (by Q rolling a large succession of double 1s while the 1 was blocked, for example)), that's a backgammon and is worth 3 points to the winner.

The basic strategy is to move pieces to the home board while leaving as few blots as possible. There are many factors to consider when moving a piece: will it cover an open, unsafe blot? if you send your opponent to the bar, is there an open spot on your home board that s/he can hit, leaving you in trouble? will it leave a blot open? Backgammon is similar to chess in that part of the strategy lies in trying to anticipate what your opponent will do next and to block hir from doing that (there are even standard opening moves). Luck and unpredictability obviously play a much larger part than would be possible in chess; however, an experienced player can learn to anticipate any possible moves, even the huge probability trees, and plan for nearly every eventuality. The luck factor is usually what attracts or repels people to (or from) this game; most people who play one tend to avoid the other.

Spuunbenda goes futher into the strategy at the appropriately named backgammon strategies node.

The doubling cube, as we know it, is actually a modern, American invention, added to the game around 1925. (There are records of a similar device in use in a backgammon-like game in the 17th century, but its use seems to have died out in the intervening years). Some sources say that the change of scope this added to the game helped boost backgammon's popularity in the States. The cube itself is not well known outside of the USA, and even then it's purely optional.

The cube has the first six powers of 2 printed on individual sides. It is set aside at the beginning of the game. If one player thinks s/he has an advantage (or is just feeling lucky), s/he can offer the cube to hir opponent. If s/he agrees, s/he becomes the owner of the cube, the stakes of the game are doubled, and the owner displays the cube with the 2 facing up. The cube can then be offered back to the first doubler; on acceptance, the stakes are again doubled (to 4x) and the new owner displays the cube at 4.

If the doubling is ever refused, the refuser forfiets the game and any points at stake (i.e. if o refuses Q's initial doubling, Q wins for one point; if Q refuses the third doubling, o gets 8 points).

Please also see Spuunbenda's writeup under doubling cube for a more in-depth discussion on how to use this device.

The origins of the game are lost to history. Some say that Ardshir of the Sasanidi dynasty, king of Persia during the 3d century, was the inventor. The sage Qaflan is attributed as the creator in Indian legend. It is known that the Romans played a similar game, "Duodecim scripta", the "twelve lines". A mural found in Pompeii shows two people being thrown out of a pub for fighting over this game. At some point, the rules were further refined and the game renamed "Tabula", possibly during the first century AD.

The 24 arrows on the board are said to represent the 24 hours in a day, the division into 12 on each side to represent the months of the year, the 30 pieces to represent the days of the month. Even the color of the pieces are supposed to represent night and day. Much of this is simply speculation, however. Noone is sure how the rules were formalized.

The Backgammon FAQ is located at has a list of other games that can be played on a backgammon board. Unfortunately, most of them require some knowledge of backgammon rules to start with.
Play online at I've never been here, so i don't know what the 'scene' is like. also offers online backgammon, and claims to teach players as well.
The history came from
More info on the doubling cube was from Morehead + Mott-Smith's Hoyle's 8 Favorite Games, Signet Publishing 2001; from; and from outside help.

Back"gam`mon (?), n. [Origin unknown; perhaps fr.Dan. bakke tray + E. game; or very likely the first part is from E.back, adv., and the game is so called because the men are often set back.]

A game of chance and skill, played by two persons on a "board" marked off into twenty-four spaces called "points". Each player has fifteen pieces, or "men", the movements of which from point to point are determined by throwing dice. Formerly called tables.

Backgammon board , a board for playing backgammon, often made in the form of two rectangular trays hinged together, each tray containing two "tables".


© Webster 1913.

Back"gam`mon, v. i.

In the game of backgammon, to beat by ending the game before the loser is clear of his first "table".


© Webster 1913.

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