Floppy disk sizes ( was Re: Compaq Portable III fails POST? )

Early 3.5" disks had a manual shutter, you had to slide it open before inserting the disk in the drive, and squeeze the corner of the disk to close it after ejecting the disk. Drives designed for those disks only couldn't take the now-standard disks with automatic shutters because they lacked the lever to open the shutter. AFAIK those disk could be used in later type drives withuut problems (such drives would open the shutters on old disks automatically, but you still had to squeeze the corner to close them after ejection) Was there an earlier type with no shutter at all? At one point HP offered an retrofit kit to update old drives to open the automatic shutters of the new-type of disk. I assume it consisted of a new disk holder/eject mechanism, but I don't know for sure. -tony