(Artículo de Wikipedia)
The Spanish dollar (also known as "pieces of eight" or the eight real coin) is actually the silver coin, worth eight reales, that was minted in the Spanish Empire after a Spanish currency reform in 1497. It was legal tender in the United States until an Act of the United States Congress discontinued the practice in 1857. Through widespread use in the Americas and the Far East, it was nearly a world currency by the late 18th century. Many existing currencies, such as the Canadian dollar, United States dollar and the Chinese yuan, are based on the Spanish dollar.
Today the term peso is sometimes used interchangeably to include the historic Spanish eight real coin. This is primarily because pesos were of similar weight and diameter to the eight real coin. However the term peso did not appear on Spanish coinage until 1864, and it is more accurate to refer to the older coinage as the eight real coin, which was also called the Spanish dollar or colloquially "pieces of eight."
The Coinage Act of 1792 created the United States Mint, but the first U.S. dollars were not as popular as the Spanish dollars, which were heavier and were made of finer silver. An eight real coin nominally weighed 550.209 Spanish grains, which is 423.900 troy/avoirdupois grains (0.883125 troy ounce or 27.468 grams), .93055 fine: so contained 0.821791 troy ounce (25.560 grams) fine silver. Its weight and purity varied significantly between mints and over the centuries. In contrast, the Coinage Act of 1792 specified that the U.S. dollar would contain 371 4/16 grain (24.1 g) pure or 416 grain (27.0 g) standard silver.
The coins had a nominal value of eight reales ("royals"). The coins were often physically cut into eight "bits", or sometimes four quarters, to make smaller change. This is the origin of the colloquial name pieces of eight for the coin, and of "quarter" and "two bits" for twenty-five cents in the United States.
Prior to the American Revolution there was, due to British mercantilist policies, a chronic shortage of British currency in its colonies. Trade was often conducted using Spanish dollars. Spanish coinage was legal tender in the United States until an Act of Congress discontinued the practice in 1857. The pricing of equities on U.S. stock exchanges in 1/8 dollar denominations persisted until the New York Stock Exchange converted to pricing in sixteenths of a dollar on June 24, 1997, to be followed shortly after by decimal pricing.
Long tied to the lore of piracy, "pieces of eight" were manufactured in the Americas and transported in bulk back to Spain (to pay for wars and various other things), making them a very tempting target for seagoing pirates. Some pirates were among the richest people in the world. The Manila Galleon transported Mexican silver to Manila, where it would be exchanged for Chinese goods, since silver was the only foreign commodity China would take. In oriental trade, Spanish dollars were often stamped with Chinese characters known as "chop marks" which indicate that that particular coin had been assayed by a well-known merchant and determined genuine.
Thanks to the vast silver deposits that were found in Mexico (for example, at Taxco and Zacatecas) and Potosí in modern-day Bolivia, and to silver from Spain's possessions throughout the Americas, mints in Mexico and Peru also began to strike the coin.
Millions of Spanish dollars were minted over the course of several centuries. They were among the most widely circulating coins of the colonial period in the Americas, and were still in use in North America and in South-East Asia in the 19th century. They had a value of one dollar when circulating in the United States.
The coin is roughly equivalent to the silver thaler issued in Bohemia and elsewhere since 1517. The German name "thaler" (pronounced "tah-ler" — and "dahler" in Low German) became dollar in French and English.