Because it was introduced in North America 35 years ago this week, we’re spending this week talking about the legacy of the Sony Walkman. The very first model carried the designation TPS-L2 and was the size of a paperback book. It came with a long shoulder strap and with something that could used to attach the thing to your belt. Believe it or not, the thing was originally a flop. In the first month, only 3,000 units were sold. But after they spread from Japan to other countries, they became a sensation. They were the smartphones of their day. Everyone had to have one. Since then, there have been more than 300 different Walkman models, ranging from cassette players to CD players and MP3 players and even video units. Hundreds of millions of units have been sold—and in some parts of the world, you can still buy a Sony cassette Walkman.