The exchange rate was pegged back in 1980 and hasn't changed ever since.
One interesting fact about Bahrain is that Saudi riyal money is also officially accepted at most points of sale alongside the principal currency. This is due to the close economic cooperation between the two countries and their geographic proximity. The dinar rate is also pegged to riyal: 1 dinar is equal to 10 riyals.
The value of Bahrain's currency is economically supported by the considerable oil and natural gas reserves, which are exported by the country to the world market.
Before becoming an oil producing country, the economy of Bahrain relied on pearl fishery as their top money making industry. However, with the introduction of cultured pearl farming in Japan in 1930 or so, the country stopped the pearl hunting activities.