Via a Hacker News post [ https://news.ycombinator.com/item?id=24243284 ]:
All disk drives connected to the Serial Bus of a Commodore 64 speak the Commodore DOS protocol, from the popular 1541 5.25″ drive to the modern sd2iec SD card interfaces. CMDR-DOS is a new and open source implementation of the Commodore DOS protocol, using SD cards with the FAT32 filesystem and supporting advances features like partitions, subdirectories and timestamps – and running on a 65c02!
It is the built-in DOS of the Commander X16, and runs on the main CPU, so the KERNAL API (
ciout) calls directly into the DOS implementation. This allows
LOADspeeds of about 140 KB/sec on an 8 MHz system.