Before DVD players came out, videocassette recorders played analog videos using magnetism. VCRs came to the United States in 1977, a year after debuting in Japan.
VCRs play VHS (video home system) tapes that look a little like larger versions of the cassette tapes you can play in a tape deck. The standard size VHS tape contains 800 feet of half-inch wide Mylar (polyester resin) tape. The Mylar’s oxide coating gives the tape its magnetic properties.
VCR players can play videotapes as well as record live TV onto tape.
Inside a videocassette’s plastic casing, its tape is wrapped around two spools that have spring-loaded locks to keep the tape taut. When the tape is placed inside the VCR, a lever opens the door on the plastic casing to expose the tape. A pin is inserted into a hole in the casing that releases the locks so that the tape can be unspooled. The tape is then pulled out and wrapped around a configuration of rollers and drumhead in a way that resembles the belt drive in a car.
Inside the VCR, videocassette tape is wound around a configuration of a drumhead and rollers.
In addition to playing back recorded videos and movies, VCR players can record live TV onto VHS tapes (the analog version of DVR/TiVo). The roller configuration allows for information to be packed on the tape without using an exorbitant length or playback speed.
The tape’s movement past the drumhead creates a magnetic field. The drumhead is set at an angle so that the tape passes over it in a helix pattern relative to its surface (this is called a helical scan). The drum rotates rapidly so that it moves with high velocity relative to the slow-moving tape.
When live TV is being recorded, video and audio signals are sent through the magnetic field. Particles on the moving tape have magnetic orientation that causes them to rearrange in response to the signal, creating an imprint on the tape. The imprints produce a dense tape track with diagonal lines.
When prerecorded videos are played, signals passed through the magnetic field by the tape’s imprinted lines are translated into video and audio signals.
VCRs can still be found today and bought for cheap- if you’re not interested in playing old videos, I highly recommend taking one apart.