DiskSumo is a Commodore 64 BASIC program to dump an image of the floppy disk in unit 8 (assumed to be a 1541 disk drive) over the RS-232 port via the XMODEM protocol at 300 baud. It also provides rudimentary directory-listing and dumb-terminal functions.
The file downloaded on the other end of the connection is usable as-is
as a .d64 disk image file. Note, however, that it won't be able to
transfer anything sensible from disks which use copy-protection schemes.
This is the program I used to transfer my old C64 diskettes to my PC (and in fact, I concocted it for that purpose) at some time in the mid-aughts. So it can be thanked, for example, for the existence of Bubble Escape 2K.
I implemented the XMODEM protocol based on a description of it on a printout I had made of a posting on a Winnipeg BBS a decade and a half earlier. I no longer have the printout, but I believe the posting was on Eric the BBS, and the poster was Bruce Walzer.
Since I transferred all the disks that I could (and since I no longer have a physical Commodore 64, and since it is of little use on an emulator) I no longer have a need for this program.
If you have a need for this program, then the first hurdle you will have to overcome is getting it onto your Commodore 64 in the first place. You will probably need to type it in.
The program is menu-driven, so its usage should be self-explanatory. Hook up a null modem cable between the Commodore 64 and another computer, start a terminal program on that computer, and set the baud rate to 300. After starting the XMODEM upload on the Commodore 64, start an XMODEM download on the other computer. (You may have to stop the XMODEM download manually after it is finished, as XMODEM is not a very sophisticated protocol, and DiskSumo just barely implements it.)
The name "DiskSumo" started life as a typo for "DiskDump".