If this is the case, then the following should help you understand the difference. A hard disk is a Hard Drive, and is typically mounted where you cannot handle it without disassembling your computer and taking the drive apart. The 3.5 inch disk is a floppy disk. To prove this, take a diskette that you no longer need, and tear it apart. If you squeeze hard enough to split open the top, you can remove the media without much trouble.
Syquest disks are more like a removable hard disk cartridge.
The platter in a Syquest cartridge is basically the same media as a Hard Drive platter, made of metal and coated with a magnetically reactive surface. This is why you are always cautioned to keep your disks away from magnets and other sources that generate a magnetic field. The magnetic field warning is for all disk drives and diskettes. Floppy disks are a common means of storing documents, but they should not be used repeatedly for more than a 4 month semester. If you use the disk to store a document away from your computer, then you probably will not have a problem with the disk.