The 45 RPM (aka 7 inch single) plays at 45 rpm - duh. It was first introduced in 1949 by RCA (Radio Corporation of America) as a replacement for the old 78 rpm bakelite records. The first ones were mono (monaural) and have recordings on both sides of the disc. When stereophonic records came along in the 1960s, most 45 records were made in stereo. Looks like I have a huge sorting project to do with these 45's.I scored a box of about 150 of them yesterday for just ten bucks at a garage sale. One was Sky High by a UK band called Jigsaw – on the Chelsea Records label. http://tinyurl.com/abjedh
WLS and WCFL played that one incessantly in 1975 - but it is a cool song. It reached #3 on Billboard’s Hot 100 in the US.