There seems to be something called the "Jiffy protocol" used for some fast load systems. I know of the JiffyDOS product, which seems to require replacing ROMs in both the C64 and the drive, but it seems that other programs and devices (such as SD2IEC's GPL'd firmware and SDOS V1.1) also support this.
Is this protocol documented anywhere? How does it work? What libraries, software and hardware (both real and emulated) support faster disk transfers using this?