The inside of a standard floppy drive has many similarities to the inside of a hard drive. It has the same basic parts. Most floppy drives have two read/write heads, meaning that it is double-sided. One head is used to read and write data to the diskette while the other is used to erase a track before it is written to by the other head. Like a hard drive, the head mechanism is moved by the head actuator. It is a stepper motor design, much like the old hard drives. This little motor moves the heads in and out, giving them the ability to position themselves over any track on the disk. The heads use a recording method known as tunnel erasure. Basically, this recording method is a way to keep each track of data separate from the others. As the head writes the data to a track, the tunnel erase heads come along and erase the outer edges of the track, thereby creating a sharp-edged track, very distinct from the others. This keeps the data on one track from being confused with data from another track, thereby eliminating problems.
The heads are spring loaded, therefore, they are physically contacting the disk while they are reading and writing. There is a system of levers on the inside that control whether or not the heads are allowed to touch the recording medium. The mechanical frame is one system of levers that is changed when the protective window at the top of the diskette is open/closed. When the window is closed, the heads are not permitted to touch the medium. When the diskette is inserted into the floppy frive, the window opens, thereby allowing the heads to make contact and data to be changed. Even when inserted into the drive, though, a set of electronic optics checks for an opening in the lower corner of the diskette. This opening us is controlled from the outside, and controls whether or not the user wants to allow writing to the diskette.
The drive spins the disk at 300RPM or 360RPM, therefore this contact between the heads and the recording medium is not a problem to the data because friction is minimum. Some diskette makers coat the disk with Teflon, further reducing friction between the heads and the disk. Although a good idea, eventually a build-up of Teflon will form on the heads, requiring you to clean them. And, while mentioning this close contact between the heads and the disk, I should mention that this is the reason why you should be careful when handling diskettes. Dust, smoke, hair, and even fingerprints are enough to disrupt the contact between the two.
The spindle motor spins the disk. As said before, it spins the disk at 300 RPM. On old 5.25" drives, the disk is spun at 360 RPM. Older drives had the spindle motor attached to a belt system that spun the disks. These were not very reliable, and the RPM was not constant depending on the disk. Today's drives use a direct-drive system with no belts. This system has automatic torque compensation so that sticky disks are spun with greater force than a slippery one, thereby maintaining a constant 300 RPM with all disks. The newer drives have this automatic ability. The older ones require periodic adjusting. This is done using little strobe marks that are on the motor. You run the drive in fluorescent light and adjust the RPM until the marks look still, just like a car rim or wagon wheel when turned fast enough.
Underneath the drive, you have the logic board. Like the hard drive, it serves to control the internal parts of the drive and serves as an interface between these parts and the floppy drive controller. All floppy drives use the SA-400 interface, the same interface used for floppy drives for years. For this reason, any floppy drive will work with any computer, right out of the box.