Here’s an article (with slideshow) about Susan Kare, the designer of the original Mac icons- I was so familiar with the one at the left.
For those of us who started on the Mac way back when, I imagine they still are the default images we still visualize when we’re on the computer.
The difference between designing the icons back then and designing for companies like Facebook (Kare designed the icons for Facebook Gifts- which allowed users to send virtual gifts to a recipient) now:
For the Macintosh, most symbols were monochrome, needed to fit within a 16 x 16 or 32 x 32 square pixel grid, and were shorthand for computer functions.
For each Facebook gift, there was a 64 x 64 pixel canvas with virtually unlimited color. The challenge was to create images desirable enough or affecting enough or amusing enough to encourage potential gift givers to spend a dollar to enhance a message. The gifts functioned as small greeting cards, rather than digital road signs. Some gifts were more iconic and some more illustrative, but detail in this case did not impede understanding.