How does a pre-recorded MD differ from a recordable one?
Physically, a pre-recorded MD is just like CD, using the same optical parameters, material, and production methods. Only the data contents are different (compressed ATRAC audio vs. 16 bit linear PCM audio). Unlike recordable MD, pre-recorded MDs do not have the magneto-optical coating layers or the lubricating layers. They are made with the same plastic-aluminum structure as CDs, so there is no way to record or erase anything on them. Prerecorded MD’s are also read exactly like CD’s (the player focuses a laser on pits and valleys within a transparent polycarbonate substrate backed by a coating of aluminum thus reflecting or dispersing the beam). Recordable MD’s are similar, but a pre-groove replaces the pits and valleys and an MO coating replaces the aluminum one. When recording, a laser is focused from one side of the disc onto the pre-groove and heats a spot on the MO recording layer to its Curie point while a magnetic field from a head in contact with the other side of the disc alig
Physically, a pre-recorded MD is just like a CD, using the same material and same production method, only the data contents are different. Unlike recordable MD’s, pre-recorded MD’s do not have the magneto-optical coating layers or the lubricating layers. They are made of the same plastic-aluminum structure as CD’s. There is absolutely no way to record or erase anything on pre-recorded MD’s. In terms of their physical characteristics, pre-recorded MD’s are manufactured exactly like CD’s and are also read exactly like CD’s. Blank MD’s are similar but a pre-groove replaces the pits and valleys and an MO coating replaces the aluminum one. When recording, the MD machine focuses a laser on the pre-groove and heats the MO coating to the Curie point while a magnetic field aligns the metal particles (the direction depends on the data, 0 or 1). During playback, the MD machine focuses the laser on the pre-groove again, but at lower power, and registers changes in polarization (the Faraday effect)
