45mph might seem more familiar than 45rpm with that determination, of course, being dependent upon in which era you grew up. From about 1949 - 1990, the former "LP" (Long Play) records replaced by a smaller size format allowed for longer playing time in jukeboxes because they took up less space. More records. More music.
RCA 7-inch 45 rpm fine-grooved vinyl record
The 45 had the same smaller-sized groove as the LP, and the center hole was larger. 45s became popular in jukeboxes, which had previously used 78s, because 45s took up less space and you could fit more songs in the box. Suddenly jukes went from offering 24 or 40 songs on 78s to having 100 to 200 songs on 45s. 45s are also made of vinyl rather than shellac, and can hold up to about 5 minutes of music on each side. 45s are still being made in limited quantities for jukebox operators who have not upgraded to newer CD jukeboxes, so you can still get some of the latest releases on 45. [Source: history-of-rock.com]
On this day in...
1949 RCA Records issued the first ever 45rpm single, the invention of this size record made jukeboxes of the 20th century possible.