The original double-breasted jacket has six buttons from naval reefer jackets, commonly known as pea coats.
The double-breasted jacket or suit typically have one to four rows of buttons (each row containing two buttons), one or two of the rows functional - the others are decorative. Each fastening method is identified using "number-on-number" terminology (six-on-two, six-on-one,...).
Double-breasted suit jackets were popular from the mid-1930s until the late 1950s, and again from the mid-1980s to the mid-1990s.
Today, they still bring back a classic and elegant looks although they have been modernized...
There are many different kinds: 8x3, 8x4, 6x1, 6x2, 6x3, 4x1, 4x2, 2x1...
Do you think that you really know about button position on a DB?
The 6x2 is most classic and the standard and we can see a lot of people like the classic "six-on-two" (6x2) DB: