What is now referred to as the classic Chicago Blues style was developed in the late '40s and early '50s, taking Delta blues, fully amplifying it and putting it into a small-band context. Adding drums, bass, and piano (sometimes saxophones) to the basic string band and harmonica aggregation, the style created the now standard blues band lineup. The form was (and is) flexible to accommodate singers, guitarists, pianists, and harmonica players as the featured performer in front of the standard instrumentation. Later permutations of the style took place in the late '50s and early '60s, with new blood taking their cue from the lead guitar work of B.B. King and T-Bone Walker, creating the popular west side subgenre (which usually featured a horn section appended to the basic rhythm section). Although the form has also embraced rock beats, it has generally stayed within the guidelines developed in the 1950s and early '60s.