Back in the days of 35mm film, a 50mm prime was considered a 'standard' lens. That's because it gives pretty much the same perspective as viewing a scene with the human eye, without the magnification of a telephoto lens or the shrinkage a wide-angle lens uses to squeeze more into the frame.
The flexi disc (also known as a phonosheet or Soundsheet, a trademark) is a phonograph record made of a thin, flexible vinyl sheet with a molded-in spiral stylus groove, and is designed to be playable on a normal phonograph turntable.
I figured it was time to go over the various types of CDs, DVDs, and Blu-ray discs, and the drives that read and write to them. I can't blame anyone for being confused. We've got three types of optical discs (CDs, DVDs, and BDs), with five different capacities between them.