Implementations

Common software versions of Spider are included with versions of Microsoft Windows 7, Vista, ME and XP as Spider Solitaire. Spider Solitaire was introduced in the Microsoft Plus! 98 addition pack for Windows 98.^[5] The game comes in three versions of difficulty: 1, 2, or 4 suits. These play modes are equivalent to disregarding suit difference, either within the colors or altogether, and thus can be simulated in the physical card game, though the computer version aids visibility by representing all cards as spades and/or hearts.^{[citation needed]}

An earlier version was written for Windows 3.x in 1991 by John A. Junod, the original developer of WS_FTP. The final version was Windows Spider Solitaire version 92.01.04. He also wrote a DOS version called EGA-Spider with version up to 93.07.05. A similar game called Arachnid was also written for Windows 3.x in 1991 by Ian Heath, a computer science professor at the University of Southampton in the UK. The latest known version is 1.2. This game was also re-written for 32-bit operating systems and is referred to as Arachnid 32.^[6]

On Unix operating systems, an early version was developed around 1989 at Sun Microsystems. A version of Spider Solitaire typically comes bundled with both the KDE and GNOME desktop environments on other Unix-like operating systems such as Linux and BSD, under the names KPatience and AisleRiot Solitaire, respectively.

Scoring

Different software implementations of spider offer alternative scoring rules. The version from Sun Microsystems from 1989 defines the following rules in the manual: 10 points for each initially face down card that gets turned over; 15 additional points for each column where all the face-down cards have been turned over (even if you don't manage to get a space); 2 points for each card that is sitting atop the next higher card of the same suit; 50 points for each completed suit removed from the tableau (in which case you do not also score for the 12 cards sitting atop next higher cards). This yields a maximum score of 990. If you win the game with 4 or more completed suits still in the tableau, add 2 points for each suit after the first three. Thus winning with all eight suits still in the tableau yields a score of 1000.^{[citation needed]}

In the Windows versions of Spider Solitaire, the scoring is calculated with a starting score of 500. One point is subtracted for each move (including any use of an undo); 100 points are added for each in-suit stack completed.

Solvability

A detailed study has been done on the solvability of Spider solitaire games using software.^[7] Winning chances in a normal game with good play are considered to be about 1 in 3 games.^[8]