Some originals (like the Action Replay ) have conflicts with JiffyDOS. Boot with RUN/STOP held to temporarily disable JiffyDOS until you type GO 64 to re-enable.
for disk management without needing to load separate utility software. Function Key Shortcuts : Pre-assigned shortcuts for common tasks, such as: : Display disk directory. : Load or Load and Run a BASIC program. : Load a Machine Language (ML) program. Enhanced Compatibility jiffydos-c64.bin
Unlike some fast-load cartridges, it is ROM-based and works with almost all software, including those that use their own fast-loaders. The Fast Lane: Why "jiffydos-c64
The .bin extension suggests that the file is a binary image, possibly a ROM image for emulation or flashing to a device. If you're looking to use jiffydos-c64.bin for emulation or to create a compatible device: Usage : Highly recommended for C64 users looking
Where to get matching drive firmware