The entire interior assembly which you see above forms a tray which is mounted on a sliding track that allows it to move from the front of the drive to the back. A spring mounted between points "A" and "B" is always trying to pull the tray toward the front of the drive - which ejects the disk cartridge. In this picture the tray is shown in its fully "back" position, as if a disk were in the drive, but normally, with no disk in the drive, the tray would be as far to the front (to the right in this photo) as possible.
As a disk is inserted, the swing arm pawl "C" catches the edge of the disk cartridge's metal shutter and begins sliding it into the fully open position. The spring tension from this swing arm also creates a gentle opposing force to eject the cartridge from the drive.
After the disk cartridge reaches the back barrier "D" it begins pushing the entire tray assembly toward the rear of the drive.
The track in which the tray slides is angled upward so that as the tray is pushed further back by the cartridge the tray rises to meet the cartridge and the disk spindle motor "E" engages with the bottom of the disk. The gray magnetic ring around the motor's hub locks the disk's mating hub tightly to the motor.
The lever "F" is an emergency head retractor which acts to insure that the drive's heads will be mechanically retracted if power is not available to do the job electronically. So as the tray continues it's rearward travel one of two pawls extending down into the drive from the lid (not seen here) pushes this emergency head retractor forward and out of the way, freeing the heads for their eventual travel.
Meanwhile, the second lid-mounted downward extending pawl has been engaging the funky looking white cam "G", pushing it away from the center of the drive. This releases the mechanical head-lock which prevents the heads from deploying without a cartridge present.
As the tray reaches its back-most travel limit, this second pawl drops into the notch shown just above the "G" label, locking the tray at the back of the drive. Similarly, the disk cartridge has been locked into the drive by two pins "H" which engaged holes in the bottom of the cartridge as the tray was rising in its track to meet the cartridge.
When the second pawl drops into the notch in the "G" cam, a small switch mounted on the circuit board underneath the tray is activated, informing the drive's electronics that a disk cartridge has been successfully inserted and locked into place. The voice-coil head actuator "J" is given a burst of power (through the flexi-cable "K" which also carries the read/write head signals) to load the heads onto the disk.
When the drive is instructed to eject the disk, the heads are first pulled back from the disk surface and the spindle motor is stopped.
After a short delay the ejection solenoid "L" is energized to pull the cam "G" away from the second lid-mounted pawl. This unlocks the tray, allowing the spring "A-B" to pull the tray forward.
As the tray follows its track downward, it drops away from the cartridge, decoupling the spindle motor "E" from the disk hub and disengaging the two pins "H" from the cartridge. This allows the spring loaded swing-arm "C" to slide the cartridge out of the drive, closing the drive's metal shutter in the process.
Note also that manual ejection can be performed by pushing a straight pin into the rear of the drive at location "M", which also pushes the cam "G" away from the second lid-mounted pawl, thus releasing the tray and ejecting the cartridge.
The Heads and Head Loading Mechanism:
The photo to the left shows the drive's two heads "A" and "B" as they are emerging from their retracted position and moving toward the disk (toward us.) The silver bar "C" running across the top is identical to another one along the bottom. Together the two bars ride the side ramps "D" which serve to "lift and separate" the heads as they emerge and enter the Zip disk's cartridge.
Once inside the cartridge and over the disk media, the side ramps taper off (as you can see in the photo) allowing the heads to clamp down upon the rapidly rotating (2,941 rpm) disk.
You can also see the white resting place "E" to which the heads return when they are fully retracted. The fact that they clamp onto this material, sliding a bit as they come to rest, is apparently what Iomega calls their "self cleaning" technology. If so, I'm less than impressed with this aspect of the drive's design. (Though I can't say that I have a better idea off the top of my head.)