This is one of the most valued hardware add-on units for your Commodore 64 available: The ‘1541 Ultimate II’ from Gideon’s Logic. The unit is a storage solution for the Commodore 64 and 128. As it emulates a ‘real’ Commodore 1541 floppy diskdrive, pretty much all program, games, music and demos that work on the original floppy drive works on this device. All programs can be loaded from the supplied USB drive or from the internal micro SD drive. 
 
Ready to Use! The 1541 Ultimate-II supplies lots of handy features:
 
1541 Ultimate II is a complete floppy drive replacement for the Commodore 64. In addition, cartridges such as Action Replay, Final Cartridge 3 and the memory extension REU can be emulated.
 
Specification
FPGA with 700000 Gates (Xilinx Spartan XC3S700A)
 MB Flash ROM for firmware updates
32 MB SDRAM
Robust, black plastic housing
 
Features
Full and cycle accurate emulation of two genuine Commodore 1541 floppy disk drives
Supports .D64 and .G64 files reading and writing on a USB stick or MicroSD card (SD V1.1, SD V2.0 [SDHC])
FAT and FAT32 support (including subdirectories and long filenames)
ISO9660 support (reading .ISO files and accessing external CD / DVD drives via USB
Adjustable device address (ID) and ROMs (1541/1541C/1541-II or own ROM)
Battery-backed real-time clock
Command interface cartridges with UltimateDOS
Built-in SID player, Ultimate audio module
C64 cartridge emulation: Final Cartridge III, Action Replay, Retro Replay, Super Snapshot, Turbo Assembler w/ Codenet, Epyx FastLoad, Ocean/System 3 Cartridges, EasyFlash (not writing!), Normal 8 kB/16 kB cartridges (not all!)
Commodore 1750/1764 REU compatible (selectable from 128 kB to 16 MB and combined with Retro Replay or Super Snapshot)
Flexible Freezer menu (select, mount, create and open .D64 images, create new folders, delete / rename files)
Fast DMA load of individual programs (.PRG files on SD / USB and within .D64 or .T64)
Configuration with resident settings
 
Interfaces
Board connector for the C64 expansion port
IEC interface
Stereo audio output (3.5 mm jack)
USB port (only suitable for mass storage)
MicroSD-compatible card slot
6-pin serial male connector