Tetris/Rotation systems

Like many aspects of Tetris, something like the rotation of pieces may at first appear very simple and straightforward, but in practice it is very nuanced. Although all versions of Tetris allow you to rotate pieces 90 degrees, and most versions allow you to rotate them clockwise or counter-clockwise, not every version of Tetris rotates pieces quite the same way. Read more below for a better understanding.

Nintendo rotation system
The rotation system employed by the NES version of Tetris, as well as the SNES compilation of Tetris & Dr. Mario, is fairly simple. It is also known as the "right handed rotation system" for the purposes of comparison to the Game Boy version of Tetris (see below). These games don't contain more advanced movement features like wall kicks (see below) and lock delays (see ).
 * O pieces have no rotations.
 * I pieces have two rotations, favoring the lower half when horizontal, and the right half when vertical.
 * J, L, and T pieces have four rotations centered around the middle square of the three square edge.
 * While S and Z pieces have four rotations, they always favor the bottom and right sides of their rotation space (hence the "right handed" aspect of this rotation system.)

Game Boy rotation system
The rotation system employed by the Game Boy version of Tetris is nearly identical to the one found in the NES version (described above) with one exception: The S and Z pieces favor the left side of their rotation space. For this reason, this rotation system is referred to as the left-handed rotation system.

Original rotation system
The original rotation system found in a majority of the early console and computer releases of the game is identical to the Nintendo (right handed) rotation system described above, with one single exception: the I piece, when rotated horizontally, is one row of squares higher.