One or two spaces after a period?

I know this sounds mundane, but hey, ever wondered why we are now asked to space once after a period? When I was learning how to type a million years ago, the rule was to space twice after each period. When I worked for a local newspaper a while back, I was told that the reason was that it saved space in the final printed text.
 
Well, here is a brief article by Brian Klems, online editor blogger for Writer’s Digest . He explains why the big mystery about that extra space in his article, “How Many Spaces After a Period?
California
 
Well, now you know. It took me a while to get used to this. I wanted to hit that space bar twice every time I ended with a period. I still do sometimes, so every once in a while, I run the Find and Replace All feature on Word. That gets rid of those pesky spaces.
 
“I like the idea that magic can be hidden under the surface of everyday life.” — Trina Schart Hyman