A disk drive is disclosed. The disk drive can include includes a spindle motor, which can rotate a disk; an encoder, which can detect the rotational speed of the disk; an encoder holder, which secures the encoder; and a base plate, which supports the spindle motor, and in which a holder indentation is formed for inserting the encoder holder in. Certain embodiments of the invention allow easy height adjustments for the encoder holder, so that the encoder may maintain a particular distance from the disk, and also allow the encoder to be fitted onto the base plate, even in cases where the base plate has a limited mounting area.