Here you go:
Apple's floppy drives are unique in that they have almost no circuitry on the drive themselves. The drive is just a dumb set of motors and heads. The floppy drive controller chip resides on a board in the computer. This is true from the Apple II all the way up to the beige G3 and PowerBook G3. On the Apple II, it was an add-in controller card, on all Macs (again, up to the beige G3 and the last PowerBook G3 with a floppy drive,) it's on the motherboard. There is only one cable running in to an Apple floppy drive. This cable contains all of the 'raw' data pins, as well as the power to run the motors.
On a PC, much of the electronics are on the drive itself. The controller on the motherboard (or, on very early PCs, an add-in card,) is much simpler than the chip on a Mac. This is because the drive itself has some 'smarts' to it. This also means that the floppy drive needs its own separate power. The data cable carries not the raw 'straight-from-the-heads' data, but is similar in concept (if not implementation) as IDE and SCSI in that the data arrives packaged. (Note that even though my explanation is long winded, it's still technically simplified, so some things are technically inaccurate in the name of ease of understanding.)
The big deal here is that, for example, a PC that can only talk to a 720 KB floppy drive, is incapable of using a 1440 KB floppy drive. This is because the controller won't speak the same language as the drive. On a Mac, you can slap a 1.4 MB "SuperDrive" into a computer that only understands 800K drives, because the raw electronics in the drive are the same, only the read head's ability to deal with the newer disks is different. It's just that in an 800K-only computer, the drive will act exactly as an 800K drive, since the controller chip doesn't know about 1.4 MB disks.
The deal is that when Apple introduced the 1.4 MB controller chip, they not only added the ability to read and write High Density disks, but they changed the raw method in which the disks are read to and written from to be the same physical style as PC disks. Then all it took was software to be able to read and write PC disks. Unfortunately, because of the difference in the physical style of writing lower-density disks, PCs could not just have software to let them read Mac lower-density disks.
But, the ability to read and write older 400K and 800K Mac disks remained. My PowerBook 100 running System 6 has no problems reading my MacWrite 1.0 disk from an original Macintosh 128k.
Because the two mechanisms are so different (Mac vs. PC) anything[/i that assumes a PC-style floppy drive (wether an actual PC, or a USB floppy drive case,) will not work with a Macintosh floppy drive, and therefore, no Macintosh 400K or 800K disks. (In spite of the similar nature of notebook floppy drives on PCs vs. Macs, PC notebook drives still use the same PC floppy interface, only with a smaller physical plug; and Mac drives still use the same Mac floppy interface, only with a smaller physical plug.)
Finally, the PC floppy interface predates IDE (Properly called "ATA") by quite a few years, and is a completely separate interface. You can *NOT* plug a PC floppy drive (of any kind) into a PC ATA controller (of any kind.) (Just as you cannot plug a Mac floppy drive into a SCSI port.) It just so happens that many PC notebooks (and even a few Mac notebooks,) used the same physical 'expansion bay' for both floppy drives and hard drives or ATA optical drives. The electrical signal is 100% separate, though. They go through the same physical plug, but the physical plug carries both kinds of signals on different pins. The device plugged in is just wired to the proper pins. (This idea exists in the new notebook computer expansion card "ExpressCard", used on the MacBook Pros as well as many PC notebooks. The slot contains both pins for PCI Express as well as USB. The card manufacturer decides which set of pins they want to use. For example, I have a FireWire 800 card that uses the PCI Express pins, and a flash memory card reader that uses the USB pins. So in System Profiler, one appears under "PCI Express", one appears under "USB".)