Microsoft FreeCell

FreeCell, as included in Microsoft Windows, is a computer implementation of the card game FreeCell.

History
The first computer version of the game is believed to have been created by Paul Alfille in 1978 for the PLATO computer system. Microsoft developer Jim Horne, who learned the game from the PLATO system, implemented a version with color graphics for Microsoft Windows. It was first included with Win32s as an application that enabled the testing of the 32-bit thunking layer to ensure that it was installed properly. It was later included in Microsoft Entertainment Pack Volume 2 and later the Best of Microsoft Entertainment Pack. However, FreeCell remained relatively obscure until it was released as part of Windows 95. In Windows XP, Windows Vista and Windows 7, Microsoft FreeCell was extended to support a total of 1 million card deals. While not released as part of Windows 10, it was made available as part of the Microsoft Solitaire Collection

Variations
Today, there are FreeCell implementations for nearly every modern operating system, as it was one of the few games pre-installed with every copy of Microsoft Windows prior to Windows 10. Prior to Windows Vista, the versions for Microsoft Windows have been limited in their player assistance features, such as retraction of moves. The Windows Vista FreeCell implementation contains basic hints and unlimited move retraction, and the option to restart the game. Some features have been removed entirely, such as the flashing screen to warn the player of one move remaining.

Easter eggs
In the earliest versions, games numbered -1 and -2 were included as a kind of easter egg to demonstrate that there were some possible card combinations that clearly could not be won. Following that, the cards are arranged in order of value, such as King, Queen, Jack, 10, 9 and 8 in the first four piles, and the remaining numbers in the other.

In versions prior to Windows Vista, if the user pushes the combination of Ctrl+Shift+F10 at any time during the game, the user will be presented with a tool used by the developers during testing.

In the Windows Vista and Windows 7 versions, if the user hits 'Select Game' and types -3 or -4 in the dialog box, then, when the game loads, drags an ace to the suit home pile, the other cards will automatically follow onto the suit home pile, winning the game.

Solving
There are 52! (i.e., 52 factorial), or approximately 8×1067, unique deals. However, some games are effectively identical to others because suits assigned to cards are arbitrary or columns can be swapped. After taking these factors into account, there are approximately 1.75×1064 unique games.

The original FreeCell application included 32,000 games, generated by a 15-bit random number seed. These games are known as the "Microsoft 32,000". Later versions of FreeCell include more games, some over one million, of which the original 32,000 are always a subset. All hands in the Microsoft 32,000 have been beaten except for game #11982.

A statement in the original Help file remains through modern Microsoft versions: "It is believed (although not proven) that every game is winnable." This statement is technically incorrect. Selecting games #-1 or -2 presents a counter-example. Even within the standard hands: 1 to 32,000 there is one which is not winnable (see below).

The Internet FreeCell Project
When FreeCell became very popular during the 1990s it was not clear which of the 32,000 deals in the program were solvable. To clarify the situation, Dave Ring started The Internet FreeCell Project and took on the challenge of trying to solve all the deals using human solvers. Ring assigned 100 consecutive games chunks across volunteering human solvers and collected the games that they reported to be unsolvable, and assigned them to other people. This project used the power of crowdsourcing to quickly converge on the answer. The project was finished in October 1995, and only one game defied every human player's attempt: #11,982.

Unsolvable combinations
Out of the current Microsoft Windows games, there are eight that are unsolvable: the games numbered 11,982; 146,692; 186,216; 455,889; 495,505; 512,118; 517,776 and 781,948. Exhaustive search has shown that 5 free cells (rather than the standard four) are required for these games. Adrian Ettlinger, using Don Woods' solver has used the same random hand generator as FreeCell to explore a further 10 million games. Of the 130 unsolvable games in the first 10 million, all of them require 5 free cells. Ryan L. Miller, with the help of others explored 100 million games, with a total of 1282 being unsolvable. This gives FreeCell a win rate of about 99.998718%.