1541 Ultimate (often abbreviated 1541U) is an peripheral, primarly an emulated floppy disk and cartridge emulator based on the FPGA Xilinx XC3S250E, for the home computer Commodore 64 (C64). It became available in 2008.
The unit is developed by Gideon Zweijtzer and is a C64-compatible cartridge that among other things contains older cartridges like Action Replay, The Final Cartridge III, Super Snapshot, Retro Replay or TurboAss with Codenet-support, and a mostly fully compatible FPGA-cloned Commodore 1541 floppy disc unit that can use C64-compatible files like .D64 disc images or .PRG files via a SD-card reader. The version plus has 32 MB RAM. It's possible to connect Ethernet to the unit.
In 2010 the 1541 Ultimate II was developed, that is smaller than the original and that has certain hardware differences like USB interface beyond MicroSD.
A similar peripheral for the same need is the MMC64 developed in 2005.