Your impression is wrong. All Apple SuperDrives are capable of reading, writing and formatting HD, DD and SD disks at 1.44MB, 800K and/or 400K capacities. Only the OS and disk copy software limit compatibility. Disk Copy 4.2, or 6.x are more than capable of formatting and copying any of these formats, as well as PC and I think even Apple II. Only certain OS versions prevents access to certain formats via the Finder. Since your PM 7500 shipped with OS 7.5.2 (one of the last operating system 800K drive Macs can use), you're going to run into certain limitations making 400/800K disks. And if you are running 7.6 or above, then you are really going to have trouble. Best to stick with System 6 or earlier, or follow the directions closely on the earlymacintosh website, noting the caveats that you should never try to mount a 400/800K disk image or read a 400/800K disk on any OS above 7.5.5! Though I try to avoid System 7 altogether depending As I've had mixed results. And keep in mind 7.5 breaks the ability of the Finder to even format a 400K disk, along with a laundry list of other incompatibilities intoruced with System 7 - so its no wonder this system causes problems.