I was taught typing on electric typewriters in junior high, and yes 2 spaces after a period.
Which is strange, because my first typing experience was on Apple IIe's in grade school. I don't recall any typing instruction back then, so probably my double space habit comes from the electric typewriter instruction.
Dr.[space]Pepper is a soft drink.[space][space]This is a new sentence. Actually, "Dr Pepper" doesn't use a period so the point is void, but there's definitely some potential semantic (and display) differences between the periods in (eg) N.A.S.A. and the periods at end of a sentence. Not quite as straightforward as you might think.
The books go into it, and LaTeX has \. for periods that are not sentence-stops (there's even more, as word-breaking and line-breaking come into play, as you don't want to end a line with Dr. when it's part of a name, etc.
Which is strange, because my first typing experience was on Apple IIe's in grade school. I don't recall any typing instruction back then, so probably my double space habit comes from the electric typewriter instruction.