Random Generator generates a sequence of all seven one-sided tetrominoes (I, J, L, O, S, T, Z) permuted randomly, as if they were drawn from a bag. Then it deals all seven tetrominoes to the piece sequence before generating another bag. There are 7!, or 5,040, permutations of seven elements, and it is believed that Tetris assigns a nearly equal probability to each of these, making it much less likely that the player will get an obscenely long run without a desired tetromino. It can produce a maximum of 12 tetrominoes between one I and the next I, and a run
Despite the generic sounding name, presumed employees of BPS are known to treat the term "Random Generator" as a unique name, referring only to this particular algorithm.
While the number of tetrominoes in a single bag is usually 7, some games use a different number. The public beta of Tetris Online (Japan) used an 8-bag randomizer for the player. Not all guideline-compliant games use the Random Generator in all modes. Tetris Worlds and Tetris Green, for instance, use a different randomizer in their Square modes, and TGM3 uses the TGM randomizer even when the game is set to "World" mode.