All color monitors or televisions must be de-gaussed occasionally. They generally do this automatically when the unit is turned on. Some have a de-gauss button. This is done to reduce the image and color distortion that is caused when the steel shadow mask behind the surface of the tube becomes magnetized. It is critical that a magnet never be put near the screen, as it will result in a colored blotch which may not be removable.
Speakers are a good source of unwanted magnetic fields.
The monitor itself emits magnetic fields also. It is not advisable to store disks or magnetic tape on or near the monitors or television sets. The de-gauss coil around the edge of the tube can put out a fairly strong field which may erase data or signals on the tape. The file system is what keeps track of where your data is and how to retrieve it when you need it. Basically it consists of a directory of file and folder names, and a pointer to a location on the disk where that file's data resides.