The dumping tools for OSI are stand-alone programs, not based on a particular OS.
There are two choices.
DiskTool is a newer program that can read/dump and write floppy images on OSI. Its a bit bigger than it's predecessor
OSIDump, but both will work to dump floppies. (If you have a spare floppy disk, it's better to use DiskTool and write the included bootable disk image to your floppy for future use & quick loading.) OSIDump can only read disks, but it is a bit smaller & uses less RAM & thus somewhat faster to load via serial port.
The procedure to get going is the same for either version.
First you will need a terminal program that can send & receive ASCII and well as Xmodem/CRC or Xmodem/1K.
I've used Tera Term with good success. You can search for it to download on the official Japanese site, but I've had problems with the site timing out lately. However I have a copy on my web page at
https://osi.marks-lab.com/software/file ... -4.106.exe for TeraTerm with installer or
https://osi.marks-lab.com/software/file ... -4.106.zip for Tera Term archive only.
Download Disktool.zip or OSIDump.zip and extract the included ".LOD" file somewhere handy.
Connect to your OSI via serial port with the terminal program.
<RESET> the OSI, enter the monitor by typing 'M' and press 'L' to load from the serial port.
Next use File/Send File.... to upload the ".LOD" file, DiskTool.LOD or OSIDump.lod eventually you should see a message on your OSI stating the program is on serial now. At this point all interaction with the program is done with the terminal.
The dump process can occur at the standard speed or 16x speed. This is recommended for 300bps connections as you can go to 4800. If you are already at 9600 or higher it may make the speed too high. If you change the transfer speed in the program, make sure to change the terminal program as well. 5.25" disk images are ~90K and would take hours at 300baud!
Dumps can be done as ASCII Hexadecimal transfers, but for fastest speed, choose Xmodem/crc as the file is transferred in binary, and is 1/2 the size.
After setting speed and hex/xmodem transfer, select '1' from the menu to start the dump, insert the floppy in the OSI and get ready to receive a file on the term program. Press a key to start transfer. For Xmodem you will be prompted to begin receiving via xmodem. With teraterm select File/Transfer/Xmodem/Receive... and ensure binary & crc options are checked. Choose a filename like "Disk1.65d" for Xmodem transfers as that extension is known by WinOSI. Hex dumps will have to be dehexed before use.
After the transfer you should end up back at the program's menu for another go.
Anyway it's all pretty easy once you get going, just ask if you have any questions.
Oh, if you choose to use Disktool, you can write a disk using the file "DiskTool5.65d" and you will be able to boot that instead of having to reupload the program via serial in the future. It doesn't use an OS on the disk, just a custom loader to boot disktool, but it looks like an OS65Dv3 floppy. (The program to make the bootable disk image is named "BootThis" also on the tools page.
Good Luck!
-Mark