According to the official ECMA specification Sony designed the UMD to support two possible future enhancements and products.
[1]
1. Protective Shutter: Similar to the MiniDisc and 3 1/2" floppy disc, this protective shutter will shield the inner disc from accidental contact. These disks if ever produced will still be compatible with some legacy UMD devices, including the
PSP-1000 series. However, they would not be compatible with the
PSP-2000 series[
dubious – discuss].
2. Auto-Loading: UMDs were designed for possible future slot loading devices with Auto-Loading mechanisms. These would be very similar to the auto-loading mechanism used in slot loading MiniDisc home and car decks. It would also be similar to the VHS U-Matic auto-loading mechanism. Unlike the current clamshell loading design the PSP uses, a slot loading device using an Auto-Loading mechanism would be motorized and completely automatic. You would insert the disc into the device slot, similar to the way you insert a VHS cassette into a VCR, and a disc into the PS3, and as you begin to insert it, the motorized mechanism would then take over and completely draw the disc inside the drive, and complete the loading process. The disc would also be ejected fully automatically by the motorized mechanism, like a VCR. This would also mean that power would be required in order to insert or eject a disc.