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[ The PC Guide | Systems and Components Reference Guide | Floppy Disk Drives | Floppy Disk Drive Construction and Operation ]

Disk Change Sensor

Modern floppy drives incorporate a special sensor and a signal on the floppy cable that work in conjunction to tell the floppy controller when a disk is ejected and a new one inserted. This signal is used for performance reasons, as keeping track of when the disk is changed also means that the system knows when it hasn't changed. Knowing this saves the system from having to constantly re-examine the disk each time the floppy is accessed to see what's there. Otherwise each time you referenced the disk, the disk's structures would have to be re-examined, causing a great performance penalty.

Occasionally problems can cause the disk-change sensor or circuitry to malfunction, causing strange problems as a result. Typically what happens is that you change the disk but the system doesn't recognize it and thinks the old one is still in there. So when you try to access a file that is on the new disk, it will say the file wasn't found. In reality, it isn't even looking for the file, it is just checking the contents of the last disk that it still has in memory. Also, if you try to write to the new disk you will likely scramble its contents, because the controller will think it is writing the old disk.

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