Pianos typically have 88 keys, of which 52 are white keys and 36 are black keys. These keys are divided into 9 groups, of which 7 groups are complete, each with 7 white keys and 5 black keys, while the other two groups are incomplete. The black and white keys alternate to form the piano keyboard. In the piano, the middle key group is called the "small octave group," which includes middle C (C4) and the surrounding notes. Starting from this key group, the groups to the right (upwards) are "small octave two," "small octave three," "small octave four," and "small octave five," with each group's notes being one octave higher than the previous group. Similarly, the groups to the left (downwards) are "small octave," "large octave," "large octave one," and "large octave two," with each group's notes being one octave lower than the previous group. In the "large octave two" and "large octave one," there are only two notes, A2 and B2, so they are referred to as "incomplete groups." In the other 7 complete groups, the black keys are formed by the positions between the first two white keys and the last three white keys, meaning that each group's black keys consist of two semitones. The layout of the piano keyboard is carefully designed to allow performers to easily play the pitches and rhythms required in various musical works.