Nothing teaches the arcana of iPod models as thoroughly as a trip through Craigslist, as I recently discovered when looking for my first (cheap, second-hand) iPod. To the untrained eye, they sure all look the same, don’t they?

But subtle distinctions tell the story at a glance. And here they are, gleaned mostly from Apple’s own ”Identifying iPod Models." (Other sources: Apple’s hardware specifications site and Wikipedia.)

FIRST GENERATION: The only model with a mechanical scroll wheel. You run your finger over it, and it actually, physically moves! How 20th century.

SECOND GENERATION: Buttons are curved around the scroll wheel as in the First Generation iPod, but the scroll wheel itself is touch-sensitive.

THIRD GENERATION: Buttons appear in a row above the scroll wheel.

FOURTH GENERATION: Buttons are flat on the scroll wheel itself, forming the so-called “click wheel”. The second revision of this iPod was the first to have a color display.

FIFTH GENERATION: Has a larger screen than previous models, available in black and most importantly can play videos.

Then there are the nanos, minis, and shuffles. Ah, it all makes me nostalgic for the days when a dozen variations of “Power Mac” scrapped for position in the marketplace.