45' s

One of the joys of being a teenage music fan for me, was the excitement of visiting the Record Store on a Saturday morning to check out the new releases, which in those days in Britain, were issued on Fridays.
However, before that, the music in our home was usually bought by my Mother and were big, clumsy, breakable 78 RPM records.
I do remember buying my first 7-inch vinyl single and it was a particularly momentous choice; one which has gone on to become a rarity: Elvis Presley's Heartbreak Hotel on HMV, not RCA.

History of singles, (thank you Wikipedia.)

By about 1910,  the 10-inch 78-rpm shellac disc had become the most commonly-used format.
The advent of the new system was not unveiled suddenly one day at a "Press Conference". 
There was plenty of information 'leaked' to the public about the new 45 rpm system through front-page articles in Billboard magazine on 4 December 1948 and again on 8 January 1949. RCA was trying to blunt the lead Columbia had established in releasing their ​33 ¹⁄₃  LP system back in June 1948.

The 7-inch 45 rpm record was released 31 March 1949 by RCA Victor as a smaller, more durable and higher-fidelity replacement for the 78 RPM shellac discs.

The first regular production 45 rpm record pressed was "PeeWee the Piccolo" RCA Victor 47-0146 pressed 7 December 1948 at the Sherman Avenue plant in Indianapolis.

So began an era where these 7-inch discs were the basis of so many great parties enjoyed by the young baby boomers, moving through their school and college days. Of course, that included me!