What the M means

A note that one of the places where online publishing and traditional publishing collide is on the meaning of "M". Don Park has a comment about Windows XP SP2 in which he says downloads will be limited to 2.5M downloads/day. In the traditional publishing world that would be 2,500 not the 2,500,000 meant by the post. Ad pricing is always expressed in CPM - or cost per thousand. The world of traditional publishing is tied to M, from the Roman Numeral M, meaning 1,000.