How does social class may or can affect the medical field?

Is all optical disks like CD/DVD/BD store data magnetically and deos magnetic field affect the data on it?

• So far I know, the optical disks has got the reader and writer made of laser ray. By the heat of laser it is burnt and the reflection of laser beam on the disk's different sector. but the storage is in magnetic form. The burning process changes the magnetic field of the disk as per desire of desired the data to be recorded. The field is stored on the disk and the film is of a metal alloy having magnetic field. The whole disk can be erased by keeping the disk in a magnetic field/near a magnet/keeping it in front of speaker. But I do not know the exact reliable source of this data. Can anybody help me about the exact fact on this idea? I may be wrong, but where can I get the exact data? Somebody claims that the optical disks are not affected by magnetic field and it only keeps the data without involving magnetic field and finally there is no connection between these disks and magnetic field! Anybody there to clarify my broken knowledge?

• Answer:

  CD/DVD/BD media is purely optical. The metal in the disc is just a reflector. Data in a commercially mass manufactured disc is pressed into the polycarbonate plastic, with just the reflector. Writable discs have a dye, which is altered by the burning laser. There uses to be Mageneto-Optical discs, and apart from Minidiscs, I have not heard of them a comsumer products. Minidisc, at least, wrote discs by using the laser to heat the MO layer to the Curie point, and an electromagnet set the dye to the intended state. That said, the drives to use magnets and coils to run the motors and focus coils in optical drives.