A Dictionary of Music and Musicians/Row of Keys
ROW OF KEYS. A single clavier or manual. An instrument having two or more rows of keys is one having two or more manuals. The term 'row of keys' is, when speaking of an organ, not applied to a pedal-clavier from the simple fact that one 'row of keys' is all that is required by the feet; two rows of pedal-keys have, it is true, been sometimes constructed, but they have always been found unnecessary, and generally unmanageable. Harpsichords had often two rows of keys, one sounding less noisy wires than the other [App. p.776 "one fitted with jacks more finely quilled, and therefore less powerful, than those connected with the other manual"]; some mechanical change of that sort being the only means of obtaining a softer or louder tone in that instrument.
[ J. S. ]