Comcast is offering a one-gigabit service aimed at small-and medium-sized businesses in Atlanta. The Comcast service joins a number of other fast internet services being rolled out in the area, including its own earlier offerings for businesses and families. The gigabit skirmish has brought down pricing for the super-fast speeds, which can cut the download times for HD movies to a fraction of a minute, or shorten the time to transfer a data-heavy file such as an MRI medical scan. The fast service topped $250 a month initially at some companies, but has since dropped to $70 or so.