In the early days of our country, there were many different kinds of coins in use.
In the southwestern parts of the United, States close to Mexico, the Mexican peso was common, and so was a small Mexican coin called the real, which was worth 12.5 cents.
When the 25-cent piece, or quarter, came into use in America, people in the Southwest called it two bits, because it was equal to two reals.
Today, no one ever uses the expression one bit, but two bits still means a quarter, four bits is 50 cents, and six bits is 75 cents.