[From its original value of eight reals.]
Pieces of Eight, Spanish silver coins of eight reals (eight bits), first authorized in 1497. Also known as pesos and Spanish dollars, they were minted in enormous quantities and soon became recognized as a reliable medium of exchange in the European colonies of North America. Subsidiary coins—four reals (half dollar, four bits) and two reals (quarter dollar, two bits)—were also minted. In 1728, Spain began coinage of the milled dollar to replace the piece of eight. The Coinage Act of 1792 made the dollar the new nation's official currency and fixed it at approximately the same weight of silver as the Spanish peso.
Bibliography
Brock, Leslie V. The Currency of the American Colonies, 1700– 1764: A Study in Colonial Finance and Imperial Relations. New York: Arno Press, 1975.
McCusker, John J. Money and Exchange in Europe and America, 1600–1775. Chapel Hill: University of North Carolina Press, 1978.