The wing-shaped grand piano is the preferred piano for concert performances. The standard keyboard range of a modern piano is 7 1/3 octaves, requiring 88 keys. Although piano technology has evolved over the past two and one half centuries, the basic mechanism has remained the same. Strings are struck by hammers operated by keys. The modern grand piano has a one-piece iron frame that allows the strings to be stretched to a high tension. Long bass strings are strung over the treble strings to save space.