EOS stands for EMULATOR OPERATING SYSTEM. It is the software that runs the Emulator 4 sampler family hardware. E-MU is constantly working on improvements to its products, and we try to make these improvements available to the largest number of customers possible. The current version of EOS software is version 4.0.1, and can be used in ANY Emulator 4 sampler family product, providing you have enough CPU Flash to accomodate the advancements made in the OS.