I guess op means memory stick/ CF/ SD card reader that fits in a 5.25" disk bay, like a (floppy) disk drive fits in a disk bay, and not a memory stick that fits inside a disk that would be very technically challenging!!
A 3.5" floppy disk adapter (Sony MSAC-FD2MA) was made, natively compatible with early Sony Mavica cameras (later models included both a 3.5" floppy bay and a Memory Stick slot.) and DOS based Windows. The technical challenge was justified because mass storage options were limited at the time.
These Amazon reviews from 2002 show an interesting perspective on compatibility:
In a traditional Sony/Ericsson smartphone (before they switched to SD which probably still works) using the USB cable the internal Memory Stick is accessible from a Windows PC no differently than a USB thumb drive or USB HDD.
So you can format the Memory Stick from the attached PC and then install an operating system like a Linux distribution if it fits, and it will boot.
It then boots the PC. The OS of the phone does not change.
That's using the phone's Memory Stick storage as an external boot device for a PC without the actual necessity for the PC to have an internal drive for that reason.
Similarly when inserted into the USB adapter, the Memory Stick can behave about the same as a regular bootable USB thumb drive.
